GTA
Support Equipment For PCP/HPA/CO2 and springers ,rams => 3D printing and files => Topic started by: rsterne on October 21, 2023, 03:04:31 PM
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I recently purchased a Digital Force Gauge from Amazon, so that I could do some testing to better understand the tensile strength of various filament materials, and the effect of changes in printer settings on that strength....
(https://hosting.photobucket.com/images/oo221/rsterne/Digital_Force_Gauge.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Digital_Force_Gauge.JPG)
I downloaded some test samples from Thingiverse, both for printing flat to test the X-Y strength, and for printing vertical to test the Z (layer bonding) strength.... The first ones I printed were the flat ones, and I did 3 versions, with 2, 4 and 8 walls, all at 100% fill, to see if having more filament extruded parallel to the applied force was better.... The Infill is always at 100%....
(https://hosting.photobucket.com/images/oo221/rsterne/Test_Samples_2-4-8_Walls.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Test_Samples_2-4-8_Walls.JPG)
You can see the difference in the above photo.... However, when I measured the parts, the square test section, which was supposed to be 0.200" square was a bit oversize (0.206-0.210"), with an area averaging 0.0436 sq.in. (9% oversize) over 6 samples, and the holes were about 0.360" diameter.... I wanted to use 3/8" bolts/pins to pull them apart, and if the area of the test section is (0.2 x 0.2) = 0.04 sq.in. all I need to do is set the force gauge to read in lbs. and multiply by (1 / 0.04) = 25 to get the tensile strength in psi.... So, I used TinkerCad to redesign them, and design a matching vertically printed test bar, so that I can fine tune the dimensions the way I want.... Here is the first set just printed....
(https://hosting.photobucket.com/images/oo221/rsterne/New_Test_Bars_rfR6zZyvDFzVPy9N29CxNJ.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/New_Test_Bars_rfR6zZyvDFzVPy9N29CxNJ.JPG)
The vertically printed one is 10mm thick instead of 5mm at the ends (as was the original) to make sure the holes don't tear out, but the test section is still 5mm square (as designed on TinkerCad).... The holes were designed at 10mm, on 33mm centers, and the ends of the bars are 22mm wide, and the bars are 55mm long.... The test sections (which are 6mm long) are much closer to what I want, the horizontal one measures 0.194 x 0.204" for an area of 0.396 sq.in, and the vertical one measures 0.197 x 0.201" which is also 0.396 sq.in. (within 1% of desired)... The holes are the correct size, only needing a quick deburr on the corners to fit perfectly on the shank of a 3/8" bolt....
(https://hosting.photobucket.com/images/oo221/rsterne/New_Bar_Holes.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/New_Bar_Holes.JPG)
If you haven't got a deburring tool, they are cheap, and if you get the plastic blades are great for deburring holes or corners on 3D prints.... The blade spins in the handle, and it comes with 10 spare blades that store inside the handle.... 8)
(https://hosting.photobucket.com/images/oo221/rsterne/Deburring_Tool.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Deburring_Tool.JPG)
The test sections are now close enough to the correct size (0.04 sq.in) that they can be fine tuned using the slicer, as they will probably change a bit with different materials anyways.... If you want to work in Metric, to get the tensile strength in MPa (which is 1 Newton/sq.mm), set the force gauge to Newtons, and divide by 25 (assuming the test section is 5x5mm, so correct the print to those dimensions).... Attached are the files for both test bars....
Bob
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How high does your force gauge go? Looking forward to your results!
I did similar, but I was testing the effect of temperature and layer thickness on Z-strength (the weakest direction) for my different filaments, printed at 100% fill. I used a luggage scale, 50kg max I think, and had to add double pulleys to reduce the force the scale was seeing, even though I used pretty small cross-sections on my specimens. As I recall I was approaching 300lbs on the specimens, 100lbs on the scale. PETG layers bond really well!
One factor to consider is -- when printing vertical for Z testing, the area intended to break is very small cross-section, and will print very quickly per layer -- depending on your settings, it may print slower mm/s than usual to maintain "minimum time per layer" settings, or it may print the tiny layers at normal speed, heat soaking the area. Either way, it may give inaccurate results compared to what strength a normal print, with a decent sized cross-section would have. The only way I know to avoid that, is to print multiple specimens at the same time, so each one is printed at normal speed, and has a realistic time to cool before the next layer gets added. Making the cross-section area bigger would also work, but the forces involved would be more than my meager shop tools could handle.
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Excellent plan, Bob Sterne
Excellent strategy, Bob TM
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Yes, I know that the force is likely more than my 500N (50 kg-110 lb) gauge will read, so I am making a setup with (at least) 2 increases in force, using a lever, at 2X and 4X, so I can handle up to 200 kg (440 lbs), or more if I add another hole in the lever.... I'm working on the setup now, and should be able to share that within a few days.... Hopefully, a nice surprise in store for all of you!.... I will be printing multiple samples at a time, so there will be ample time for cooling between layers in the small vertical test section when doing the layers.... I am very curious about how temperature, cooling, and speed affect the layer bonding.... ;)
Bob
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So, unless I screwed up, a 0.2 x 0.2" specimen that fails at 240 lb has an ultimate strength of 6000 PSI. If so, that would seem close to the strength of the base material. Very impressive, if it is applied across the layer plane.
Any strength measure is better than none. It is probably important to apply the load at about the same rate for comparisons between print direction, or fill percentage, for example. Very slowly applied force allows the material load to even out via creep. Very fast, and shock becomes a factor.
Anyway, I have been impressed with printed PETG, both in my hands, and indirectly via parts that Bob has printed, holding up better than I expected. It has taken me awhile to trust this observation and design lighter parts for 3D printing.
I think PETG is a more durable material than PLA, despite the latter being stiffer and stronger. PETG is not as easily degraded by environmental factors; and does not creep so badly when a part is left in a vehicle in the sun.
I am sure that you have seen the video below, or ones like it. Ultimately you only have to satisfy yourselves that your prints are strong enough for purpose, rather than getting into arguments with forum members or potential customers.
Certainly, it sounds like PETG is a friendlier material to print than ABS; stronger even if the cosmetic results are not as good. But then my own printing experience is limited to a Kodama Trinus using PLA. And that was a few years back...
https://www.youtube.com/watch?v=ycGDR752fT0
https://www.youtube.com/watch?v=VunrhQzYWkg
https://www.youtube.com/watch?v=WrQiUL0jAzc
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Bob, Stefan from the CNC kitchen videos Subscriber linked has posted a number of 3D print strength comparison tests. He also posted the build of his Instron like DIY tester.
https://www.youtube.com/watch?v=uvn-J8CbtzM (https://www.youtube.com/watch?v=uvn-J8CbtzM)
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That's a very cool Tensile Strength Tester.... CNC Kitchen videos are consistently great....
Well, I have been working on the new tester, here is a photo of the progress.... The test bar is in the 2:1 position, with the 4:1 position to its left.... The slotted bar is actually parallel to the base, poor photo.... ::)
(https://hosting.photobucket.com/images/oo221/rsterne/Tensile_Tester.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Tensile_Tester.JPG)
I decided to change the design of the test bars slightly, thinning the "Z" test bar to 9mm instead of 10mm, so that it will fit in a 3/8" milled slot, and lengthening it by 7mm to allow for fillets between the 45 deg. narrowing sections and the 5mm / 0.200" square test strip.... The holes are now 40mm between centers, and the overall length is 62mm.... If a longer test section is needed, just remix the center test portion, it is 5 x 5 mm and by default is 6mm long.... Here are the new test bars....
(https://hosting.photobucket.com/images/oo221/rsterne/Screenshot_2023-10-24_162229.png) (https://hosting.photobucket.com/images/oo221/rsterne/Screenshot_2023-10-24_162229.png)
This should allow a smoother transition of the force into the test section.... The new .stl files are below....
Bob
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I got it finished to the point of operation today....
(https://hosting.photobucket.com/images/oo221/rsterne/Working_at_Last.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Working_at_Last.JPG)
Yes, it's mounted on my lathe!.... By using 45 RPM and 0.0044" feed per turn, I get 0.198" per minute, which is within a whisker of the 5mm/min. pull speed that is the standard for tensile strength tests (according to the internet).... The main part is mounted in the "T-Slot" on the carriage, by removing the tool post and turning the compound feed parallel to the bed.... I move the carriage so that I can get the test coupon in place, drop in the 3/8" quick pins (cut off bolts), engage the half nuts to the lead screw, and then back the compound feed out until the force meter just moves.... Flip the switch on the lathe, and it pulls at constant speed until the coupon breaks.... I have the force meter set to read peak force, which it holds until you can write it down, and prepare for the new test.... Here is the broken coupon, still in place....
(https://hosting.photobucket.com/images/oo221/rsterne/Broken_Sample.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Broken_Sample.JPG)
The fixed mount is bolted to a vertical aluminum bar (3/8" x 2") which is bolted to the bed below the lead screw, resting against one of the cast iron cross webs.... I used the 2:1 position for testing a "Z" sample (layer strength, about 2400 psi), and the 4:1 position for the "X" sample, where the filaments are running the length of the coupon.... It broke at just under 6500 psi.... Here is a photo of the coupons....
(https://hosting.photobucket.com/images/oo221/rsterne/Tests.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Tests.JPG)
The top one, the "Z" test failed exactly as it should, between the layers in the narrow test section....
The middle one was the current design of "XY" coupon, and it failed in the middle, but a piece blew off one side....
The bottom one is the original "XY" coupon, and it failed by delamination in the 45 deg. angle portion, rather than in the test portion.... That was the reason for the design change, and it appears I may need to make it even longer, with shallower angles or a larger radius....
All in all, I am VERY pleased with how it works.... 8)
Bob
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Bob,
You have achieved a sophisticated test system, with minimal investment in new hardware. Very impressive.
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I wonder what I need for the angle leading into the test section so that it fails first?.... It appears that with 45 deg. it delaminates, which I guess makes sense, as the force to do so could be as low as ~ 2400 psi x 1.414 = 3394 psi.... At 30 deg. then it would be ~ 2400 x 2 = 4800 psi.... and at 20 deg. it should be ~ 2400 x 2.92 = 7000 psi, which is more than the tensile strength of ~ 6500.... Those numbers are, of course 1 / sin(angle), which I think is the force pulling the layers apart at that angle, isn't it?....
I'm going to make some XY coupons with different angles until the failure is always in the test section, hopefuly I'll learn something along the way....
Bob
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That angular consideration is an interesting question, Bob. At what point does someone argue that your coupons are not standard? Unless you are talking about leaning the standard coupon relative to the printer axis by so many degrees. If the latter, leaning the coupon surely means that the test section is also not orthogonal?
My attitude about a standard coupon or test method would be, they are a starting point, until you develop something more sensible. Then, maybe others might adopt a new standard for testing 3D printed parts.
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Bob, great work.
I found some light reading for when your next set of coupons are printing. Some of the discussion deals with optimizing the print path to avoid some of the failure modes you've seen. Of course, that gets into the question of staying representative of a typical (unoptimized) 3D print. In general, the ASTM dog bone coupon configurations tend to be longer than your initial coupons.
https://www.osti.gov/servlets/purl/1669703 (https://www.osti.gov/servlets/purl/1669703) (pdf)
https://www.mdpi.com/2073-4360/15/14/3029 (https://www.mdpi.com/2073-4360/15/14/3029)
https://www.sciencedirect.com/science/article/pii/S2238785423010578 (https://www.sciencedirect.com/science/article/pii/S2238785423010578)
Looks like a fun project.
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The ASTM coupons require a clamping system, do they not?.... I want to use the through hole type (quick and easy replacement with quick pins), so I will have to work on the center section and lead-ins to it until it breaks reliably only in the test section.... Four versions are on the printer as I type!....
It is easy to make a longer section for the XY coupons, but not so much in Z.... For example, I don't think you could print a standard ASTM Dog-Bone in Z.... I think the Z shape I have seems to work fine (pending more tests), as in reality all it it doing is testing the interlayer bonding, so the failure should always occur at the smallest area (unless there is a flaw in the print)....
Bob
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I think your configuration would accommodate a clamping approach outboard of the pins. The clamp approach would open up the geometry options and keep the stress field closer to the ASTM standard. I am thinking of a functional equivalent to the simple clamps used in the test stand from the company that makes your force gage.
www.amazon.com/Mxmoonfree-ZMF-500N-Force-Gauge-Manual/dp/B0C7VBB84D
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I like a single pin at both ends of a tensile sample: The pins make effective hinges so the system is self aligning. This avoids bending of the sample. Else, you have to grip the sample very carefully to avoid misalignment that could induce bending. The rest of the system also has to have good alignment, and constraints to avoid moving off axis. Constraining the axis could induce friction, unless you have ball slides.
Hinges are so much simper...
That amazon stand is amazingly cheap, but it has you crank by hand to produce the test force. Not a bad option, but the speed at which the force is applied is also part of the test standard. If you can't exactly match that standard, being consistent is a pretty good second. Bob's lathe setup is not desktop friendly, but it is consistent.
All that said, modifying the amazon test stand to add hinges to the jaw arrangement would take away my objections. Ball joints would be better, as they hinge in all directions. Or two hinges at 90 degrees, like a universal joint.
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Yes, I could no doubt change both the test equipment and the coupons, to be closer to the ASTM standard, but in truth I don't care.... My object is to get repeatable results to be able to explore how changes in printer settings change the results, rather than what the actual tensile strength (as per ASTM) is.... I of course want to be able to compare different filaments as well.... Anyways, today I learned more than I could have imagined, just with a few tests, all done with PLA....
First I tested the effect that changing the number of walls had.... Before I built the machine, I had already made some coupons, from the original Thingiverse design, at 5mm thick, with a 45 deg. angle.... I used 2, 4 and 8 walls, expecting that when the test section travel was completely aligned with the stress (ie all walls) the strength would maximize.... Well, that didn't occur.... Two walls at the top, 4 in the middle, and 8 at the bottom....
(https://hosting.photobucket.com/images/oo221/rsterne/2-4-8_Walls.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/2-4-8_Walls.JPG)
Here are the numbers, time to break (in seconds), stress (distance stretched at break in mm), strain at break (maximum in lbs.), and tensile strength in psi.... plus mode of failure....
2 walls - 67 sec.... 5.58 mm.... 327 lbs.... 8170 psi .... Broke across center
2 walls - 66.... 5.50.... 323.... 8070.... Broke across center
4 walls - 73.... 6.08.... 342.... 8550.... Broke across center
4 walls - 75.... 6.25.... 350.... 8760.... Broke across center
8 walls - 64.... 5.33.... 271.... 6780.... Delaminated along 45 deg. shoulders
8 walls - 56.... 4.67.... 283.... 7080.... Delaminated along 45 deg. shoulders
My conclusion is that the infill, which is 100% density of diagonal lines alternating on the 45's, is preventing the two sides of the test section from moving relative to each other, causing the delamination along the sloped shoulder.... Next, I tested a series with different shoulder angles, but all with 8 walls, expecting to see less delamination with the shallower slope, which did in fact occur.... Description below is from top to bottom in the photo....
(https://hosting.photobucket.com/images/oo221/rsterne/45-30-25-20_deg_30L-30R.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/45-30-25-20_deg_30L-30R.JPG)
At 30 deg. the strength was significantly more than at 45 deg. (top coupon), but it still failed when the slope delaminated.... With 25 deg. slopes (and 20 deg.) the tensile strength increased to be in between the 2 and 4 wall tests in the previous section, and the coupons broke across the middle.... The bottom two coupons are a 30 deg. shoulder angle with a longer test section, and a new coupon design with round ends, a 30 deg. shoulder, and a radius between the shoulder and test section.... They performed almost identically, and failed slightly before the 30 deg. sample 2nd from top in that photo.... Interestingly, all six coupons showed some delamination, whether that was the method of failure or not.... Also, all coupons tended to delaminate along the centerline.... ??? .... Here are the numbers....
45 deg.... 43.... 3.58.... 220.... 5510.... Delaminated
30 deg.... 57.... 4.75.... 300.... 7500.... Delaminated
25 deg.... 71.... 5.92.... 331.... 8270.... Broke across center, some delamination noted
20 deg.... 66.... 5.50.... 333.... 8330.... Broke across center, some delamination noted
30 Long.. 57.... 4.75.... 282.... 7040.... Delaminated
30 Rnd... 57.... 4.75.... 282.... 7060.... Delaminated
My conclusion is that for this style coupon, with these printer settings, a slope of 25 deg. or shallower is needed on the shoulder, and that there is no significant difference in the strength or failure method using a rounded coupon or radiused filled into the test section (but it uses less filament and printing time).... There appears to be a lack of bonding between the inner walls of the test section, allowing the two sides to split apart.... Possibly this is due to using 0.4mm walls (a total of 12) which take up 4.8mm in a 5mm wide part.... I am going to try using a slightly thicker wall to get the inner walls to bond better, or possibly increase the percent extrusion slightly about 100%.... I am not sure, bit I think that should tend to produce "square" filament strands instead of round one?....
By the way, my method of timing is to set the coupon up with minimal clearance to when the lead screw starts to pull on by using the compound feed, so that the starting load on the gauge is zero.... I then turn on the lathe, and start a stopwatch when the numbers start to increase, stopping it when the part breaks.... Interestingly, in the first few seconds the load increases slowly with slight pauses, until the coupon settles into full engagement with the quick pins.... The load then rises in a pretty linear fashion until a few seconds before failure, when the stress plateaus and the coupon is yielding before it breaks....
Bob
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When I did tensile testing I use to load at .050 inches per minute. Any idea of your load rate? Of course my ultimate load use to be around what your psi results. Is your pin holes slightly rounded so as you are loading the coupon you're not putting any twisting load into it?
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Robert, I am loading at 5mm (0.2") per minute, which I read somewhere is the standard load rate?.... The holes in the coupon are straight sided, but all the holes in the test machine were done on a mill, to they are as parallel as humanly possible.... There is vertical clearance on the pins so that the coupon can slide up and down to align itself horizontally with the load.... The results seem to be very consistent, so I think accuracy of the machine and coupons is not problematic....
Bob
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Most of the tensiles I tested was at.050 but there were some at .2 but it's been more than a decade since I last did any testing and can't remember what material was tested at .2.
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OK, so I tried changing the flow rate because I thought I was getting incomplete bonding between the wall layers.... I tried 110% and 120%, but since I was printing inside to outside, the coupons got slightly wider, with smaller holes, which I had to drill out to fit over the quick pins.... The 110% did increase the tensile strength of the coupon slightly (yes, I used the larger areas), but it dropped again at 120%, and the top surface was so rough I thought it might damage the nozzle, which was rattling over it!.... Here are the photos....
(https://hosting.photobucket.com/images/oo221/rsterne/100-110-120_Flow.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/100-110-120_Flow.JPG)
The top row is 100%, middle 110%, and bottom 120% flow.... I tried one more pair of coupons with only the inner walls set to 110% flow, all the other settings the normal 100%, and they gave the best results.... No photo, sorry, but here are the best tensile results to date....
30 deg. tapered.... 55 sec.... 4.58mm.... 304 lbs.... 7501 psi.... Small delamination on one shoulder....
30 deg. rounded... 68 sec.... 5.67mm.... 356 lbs.... 8785 psi.... Broke at end of test section....
These looked essentially identical to the middle row in the photo above.... I did see one thing when examining the breaks.... The bonding WAS better with the increased flow rate, which resulted in the highest strength to date....
Bob
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Sometimes too many variables just confuses the issue, even when I change them one at a time!.... Now I am seeing some failures through or around the eye for the quick pin, something I cannot have happen, and didn't see in the first rounds of testing.... All I can assume is that I an succeeding in making the test section of the coupon (5 x 5mm) strong and stiff enough that is is transferring the load too well to the ends (or actually they are breaking before it)....
(https://hosting.photobucket.com/images/oo221/rsterne/Various_Walls_Temps.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Various_Walls_Temps.JPG)
The top row is the coupons I mentioned in the last post, with 110% flow in the inner walls only.... They failed right at the end of the test (narrow) section, the one with the 30 deg. angle ripping a piece out of the wall leading to the eye, while the faired in one (right) broke right where the 8 layer walls part to wrap around the eye.... It was the strongest one yet, breaking at 8785 psi, even allowing for the wider test section from the extra flow.... However, the increased density due to the extra flow is something we would not do in practice, because of the detrimental effect on the finish, so I am dropping back to 100% flow for all testing going forward.... In addition, because some of the samples are starting to stretch for up to 30 seconds after the force peaks, I am going to time only to when the force peaks (as closely as I can), and we will call that the "Yield Strength" of the plastic, which is effectively the maximum stress you can use without seeing permanent distortion....
The second row are printed with 8 walls of 0.40" wide, at 100% flow.... That works out to only 4.8mm of walls, filling a 5mm wide part, which is why i started playing with the flow in the first place.... The angled coupon was the first one where I saw it stretch for 30 seconds after yielding, and the faired in coupon broke as it should.... Row's 2 through 4 used the "Extra alternate wall" feature to better lock in the infill....
For the third row, I changed the wall width to 0.42", so that it properly filled the 5mm test section.... Failure of the angled coupon was the same, but the faired in one ripped the outer wall from the eye.... When I looked back at the Cura Preview, I found out that increasing the wall thickness dropped the wall count around the eye to only 7 instead of the 8 previously, and I think that is why the eye failed....
The fourth row was the same as the third, but I increased the temperature to 220*C instead of the 205*C I have been using previously.... It performed great, strongest of all the coupons tested at 100% flow.... Why the angled coupons stretch, while the faired in ones break, I have no idea....
The bottom row was the same as the 4th, except instead of using 100% fill (lines at 45 deg.) for the triangles between the hole and test section, I increased the number of (possible) walls to 16 instead of 8 (7), so they were printed with no infill, just walls.... The angled coupon performed exactly the same as the other one printed at 220*C, but the faired one broke the eye!.... Now I'm getting frustrated.... ::) .... Here are the yield strength numbers for these tests....
30 deg. angled, 110% flow.... 7501 psi.... some delamination
30 rounded, 110% flow.... 8785 psi.... OK
30 angled, 100% flow, 0.40" walls, 8 alternated with 9.... 7949 psi.... stretched
30 rounded, 100% flow, 0.40" walls, 8 alternated with 9.... 8379 psi.... OK
30 angled, 0.042" walls, 8/9.... 7855 psi.... stretched
30 rounded, 0.042" walls, 8/9.... 8086 psi.... eye failed
30 angled, 220*C.... 8306 psi.... stretched
30 rounded, 220*C.... 8484 psi.... OK
30 angled, all walls.... 8348 psi.... stretched
30 rounded, all walls.... 8086 psi.... eye failed
I am going to try a different test section that is 6mm wide and the whole coupon only 4mm thick.... This will allow me to have 16 walls in the test section, and have 8 of them wrap around the eyelet on the ends.... Stand by for the results.... ;)
Bob
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Here are the first tests with the 6mm wide by 4mm thick test section.... The angles were changed to 1 in 2 (26.6 deg.).... The bottom two angled coupons had rounded ends to save material.... and became the only angled coupons to shed part of the eye!.... hmmmmmmmmmmmmmmm.... ??? .... All coupons has the outer wall printed first, to hold the dimensions better, and not have to drill for the pins....
(https://hosting.photobucket.com/images/oo221/rsterne/Wider_Test_Section.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Wider_Test_Section.JPG)
Top row was 0.38mm walls, so that 16 of them (8 per side) are 6mm wide for the test section, and also they flare out to wrap around the eye.... They didn't use the alternate extra wall function.... I used 110% flow for the inner walls....
The 2nd row was the same, but used the alternate extra wall.... Both rows performed great....
The 3rd row was also 8/9 alternating walls, but 100% flow.... The angled coupon (left) shed the eye (which I never found), the faired one was fine....
The bottom row used all walls, with no infill.... Both coupons tore the outer walls from the inner walls of the eye.... Here are the yield strengths....
27 deg. angled, 0.38mm wall, 110% flow.... 8453 psi.... stretched
27 deg. rounded, 0.38mm wall, 110% flow.... 8892 psi.... stretched
27 angled, alternate extra wall, 110% flow.... 8903 psi.... stretched
27 rounded, alternate extra wall, 110% flow.... 9046 psi.... OK
27 angled, 8/9 walls @ 100% flow, 220*C.... 7896 psi.... eye failed
27 rounded, 8/9 walls @ 100% flow, 220*C.... 8353 psi.... OK
27 angled, all walls, 220*C.... 7788 psi.... eye failed
27 rounded, all walls, 220*C.... 6004 psi!.... eye failed
It appears that the squared end on the coupon helps keep the eye from distorting and tearing out.... So, even though the rounded end saves material and looks pretty, I guess I better not use it, and see if that prevents further failures at the eye.... :-[
The highest yield strengths were once again the coupons with 110% flow on the inner walls, but the top surface of them is very rough, and it is not likely we would use that setting, so I am going to stay with 100% flow.... Using all walls seems to not be quite as strong as using the criss-crossed 100% infill for the triangles.... My guess is that the infill acts like crossbracing and helps prevent movement of the walls of the test section past where the width increases.... The alternate extra wall does indeed help lock in the infill, so I am closing in on a good coupon design....
Bob
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Bob, great work. That's a lot of interesting data. You mentioned that you were mostly interested in the relative data between the coupons rather than the absolute numbers. A filament strength number may make a useful benchmark though. Unfortunately the internet numbers for PLA are all over the place, with some below what you are getting with printed parts. It may be useful to pull on just a filament to get a number for your specific batch.
Thanks for sharing your progress.
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OK, so I redesigned the angled coupon so that the slope of the sides is 2:1, which works out to 26.6 deg.... The original ones I downloaded were 45 deg. (1:1), and the tended to pull apart on the slope, I think because the pull exceeded the layer bonding.... I got rid of the radius leading from the slope to the test section because it didn't seem to be doing and good.... I made a second version where I increased the thickness at the eye by 2mm, so there is a very shallow, stepped slope between the eye and the test section, but on the top surface only.... I ran a test at 220*C, and it seemed to work fine, so I decided to try other temperatures.... On the next set, at 210 deg. I ran out of filament, and changed to the same brand (Creality), but in white.... I ran the rest of the tests in white, it didn't really seem to matter.... Here are the spent coupons, 250*C at the top, dropping by 10* each row.... The coupons with the thicker upper surface at on the right....
(https://hosting.photobucket.com/images/oo221/rsterne/Different_Temps.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Different_Temps.JPG)
and here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Creality_PLA_Temp_fYghpp5tMDmjeqz4TcfzdL.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Creality_PLA_Temp_fYghpp5tMDmjeqz4TcfzdL.jpg)
The force required to break the constant thickness coupons tended to be higher, and varied more than the thicker ones....
Bob
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I then tested some Overture "Econo" PLA.... I did them at 190, 210, 230 and 250, top to bottom in the photo....
(https://hosting.photobucket.com/images/oo221/rsterne/Overture_Econo_PLA.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Overture_Econo_PLA.JPG)
Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Overture_Econo_PLA_Temp_1LAgS5q1ZNhhYsVe47M68F.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Overture_Econo_PLA_Temp_1LAgS5q1ZNhhYsVe47M68F.jpg)
The overall tensile (yield) strength was MUCH lower than the Creality PLA (like HALF), temperature made virtually no difference, and if you look closely at the photos, you can see the stretched portion is "crazed".... meaning it has a whitish appearance due to microfractures as the material stretches.... Not a good product if you are looking for strength in PLA, in my opinion....
Bob
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How does PETG do?
Interesting on the 2:1 difference in strength between the two brands of PLA. What's the price differential between them?
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I suppose we should give Creality filament some due respect. I've never heard it mentioned as good nor bad, so it's easy to forget about. Overture is generally considered pretty good.
This is from a "printability" standpoint -- most folks don't intentionally break their prints.
I found a similar disparity between same-brand regular black PETG and a matte black PETG. The matte was way weaker, only having ~60% the strength. Must be the additives. It looks fantastic, though.
Keep on bustin', Bob!
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Bob, this is very useful data, and I do not even run a printer. But I do designs for printing, based on assumed printed material strength.
A related field that would provide useful info, is the pull strength of 3D printed threads. The male thread would be metal, while the female thread would be printed in a "coupon" form compatible with your test rig. The sample should be able to self-align axially, similar to what your test print and pin arrangement does now.
I think many folks here would like to know how strong a 1/2" deep 1/2 - 20 printed thread is; comparing these strategies:
Thread designed to be used directly off the printer;
Designed with extra material to be chased by a tap;
Designed as an untapped hole, with thread to be fully tapped.
Certainly, the first version listed could be done the most easily, without the need to purchase a tap; assuming an appropriate threaded bolt could be sourced.
Any interest in this would be appreciated. How can we assist?
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Sub, I can do that, and when I have finished running my strength vs temp tests I will see what I can do to make up the fixtures.... I would assume you want to run two sets of tests, one with the threaded hole printed vertically (Z) and the other with it printed horizontally (X and or Y).... I only have 3/8" x 1" horizontal slots in my machine to accept the coupons, with a 3/8" hole vertically and smooth 3/8" pin (shortened bolt)....
We would need a male thread adapted to fit into the moving slot.... I would think a piece of aluminum milled to fit into the slot (and pivot loosely), drilled for the pin, with the end tapped 1/2"-20 and a piece of thread rod inserted and loctited into place should do the trick.... We might need a similar adapter for the fixed end to accept a thicker coupon that would contain the female threads.... My concern is that the strength of 1/2" depth of threads might exceed 400 lbs, as the maximum I can test (without making a new lever) is 2000N - 200 kg - 440 lbs.... and if I go more than that, I might have to brace the vertical fixed attachment to the lathe.... The leverage across the holes is already 3630 lbs, spread across two 5/16" bolts an inch apart and the fixture leaning against the cast cross brace of the bed, about an inch above that.... I can install a stay and turnbuckle to the rear of the bed, with most of the stress in that stay, but if we stay less than 400 lbs force to strip out the threads I should be OK.... Whether the lead screw thrust bearings are strong enough is another question, and I really can't risk damaging the lathe.... ::)
You would need to tell me how thick the coupon will be, and the width (I assume you would print a cube with a threaded hole).... so that I can make the adapter to suit....
Bob
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Bruce, the price difference is not proportional to the difference in strength.... I will be doing PETG shortly....
Bob
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Bruce, the price difference is not proportional to the difference in strength.... I will be doing PETG shortly....
Bob
Bob, I didn't think there would be a strong relationship between price and strength. Interesting, however, that there's such a big difference though. Could even be lot dependent. ("Lot" as in from lot to lot of the production of the filament.) If I had something "critical", I'd not be relying on previous tests, but would be testing the filament that I planned to use.
PETG would be interesting. I do most of my printing on PETG now. It seems more pliant than PLA, but it is strong and it doesn't sag in the heat. PETG also isn't brittle, like PLA can be.
I printed my AXA tool holders in both PLA and PETG, and I think the PETG ones will hold up better. Think I will replace the PLA units over time.
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I did the testing on regular Overture PLA today.... Here are the results.... Basically it is about twice as strong as their Econo PLA.... :o
(https://hosting.photobucket.com/images/oo221/rsterne/Overture_PLA_Temp_muVQ6ZXLixiYUM2JYS91br.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Overture_PLA_Temp_muVQ6ZXLixiYUM2JYS91br.jpg)
Maximum strength is reached with a nozzle temperature of 230*C, and once again the coupons with the 5mm thick ends were not as sensitive as the ones with the 4mm ends.... All coupons had a test section that is 5.6mm wide and 4mm thick.... Tests are showing great consistency....
Bob
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Thanks Bob,
My interest in printed threads at 1/2-20 would all be printed with the threads facing up on the printer platen. Other orientations would have general interest, but due to the asymmetrical printing induced threadform distortion, such threads should all be chased with a tap. Printed a little tight everywhere and then tapped.
My interest is how strong the threads are VS layer to layer adhesion of the support material; and of how the threads are generated: What percentage thread needs to be removed off a thread that screws together easily, without slop, VS one that has some play. Also, compared to a fully taped thread, and one that has been printed overly tight, then chased with a tap. What wall layer count one uses may also affect the strength of a tapped thread.
Smaller thread sized are more likely to be printed in any "cross-plane" direction or angle. I think that anything at or under 1/4" should probably always be tapped. Certainly any thread under 1 mm pitch is asking a lot of a as-printed use thread.
I appreciate that a full half inch deep thread may be too strong, so the way to handle that is testing fewer threads; until they fail at a force level your setup can handle. Perhaps starting with two threads, then three and so on. If 3 threads fail at 390 lb, then 9 could be deemed to hold 3 times as much force.
I do not think it necessary to burden you with all possible configurations, but some info on printed thread strength would be useful.
One variable that one might overlook is tread strength where clamping force is generated by tightening the screw or bolt. That making it "tight" can use up a lot of the plastic thread strength; especially for small diameters. The way plastic threads tighten up is not like metal, where there is a "wall"; that if ignored you stretch the threads or the bolt. I think plastic loads up more gradually, with more drag early on; then a much less obvious "wall".
I don't know if this aspect is outside the scope of force testing, but for all of us who stripped plastic threads because they were not "tight" yet, it might be a facet of the study. Hence my suggestion that thread engagement depth be set for tensile testing, but not torqued against anything, other the the friction in the thread generated while screwing the parts together.
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I would imagine that the wall thickness around the female thread would affect pull strength. If the wall is too thin the part will stretch in diameter and allow the thread engagement depth to go to zero. Then the test piece will slip off the metal bolt as if it were only friction coupled. Yes, the thread tips would probably get sheared off, but not the whole thread.
How thick that printed coupon wall is, will form part of the system strength, that the part designer needs to take into account. So, we have thread shear strength and we have resistance to bulging and slipping off, as system failure modes.
This suggests two types of test coupon that test different aspects. The same principles apply to metal, but the bulging and slipping off failures only occur at much thinner walls than plastic. The softer the material, the thicker the wall needs to be so it does not bulge on the OD around the threaded hole.
The above becomes obvious if you have used thread forming taps. A wall thickness that allows one to use a thread forming tap, where there is no plastic deformation of the OD (or at the outside wall), should be thick enough for tensile testing for thread shear strength. If a full thread form cannot be achieved when using a thread forming tap, because of bulging at the part OD, then shearing the thread is much less likely to be the tensile test failure mode; seen when generating a thread by means of a cutting tap or printing; assuming the same nominal thread size and material.
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This may give some idea of the pull forces that might be needed.
https://www.youtube.com/watch?v=iR6OBlSzp7I
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2000N = 200 kg. = 440 lbs is just about the maximum I can handle.... and that was for M5 threads and the infill looks like it failed first.... The threaded "cylinder" pulled out of the infill!....
Bob
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Bob,
That is impressively strong for an M5 thread. And as you say, the thread did not fail.
Stan,
Using inserts would be the smart thing to do. Assuming they are placed with appropriate alignment.
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I use heat installed inserts for the smaller threads for repetitive assembly. Probably not the right application for a 1/2-20 LDC type application that is tilt sensitive. Buckrail site says they use an e-z lock insert. Sounds like a good approach.
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From Stan's video, another one comparing types of insert:
https://www.youtube.com/watch?v=G-UF4tv3Hvc
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Threads create a very high axial tension when tightened....
https://www.engineersedge.com/calculators/torque_calc.htm
For steel threads, unlubricated (coef. friction 0.2) a 1/2" thread (pitch does not matter) tightened to just 10 in.lbs has 100 lbs. of axial (clamping) force.... At 10 ft.lbs that increases to 1600 lbf.... :o
Bob
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The coupons are acting as they should now, so unless I see a problem, I won't bother with more photos.... I will just give the results graphs....
I have read that reducing the cooling can increase the strength on PLA, so I tested that out.... I picked a temperature, and then starting with the data from the coupon I had already done (at 100% fan), I reduced the fan speed to 80%, 60%, 40%, 20% and zero, and plotted out the results.... When I used 230*C nozzle temperature, where the Overture PLA was the strongest, the strength dropped slowly as the cooling decreased (instead of increased!).... When I thought about this, it made sense, as increasing the temperature above 230 reduced the strength.... So, I dropped the temperature back to 210*C, where the strength was the lowest, as shown in Reply #31 above.... Now, I got an initial increase in strength, as shown below....
(https://hosting.photobucket.com/images/oo221/rsterne/Overture_PLA_Cooling_210.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Overture_PLA_Cooling_210.jpg)
The strength peaked at 40% cooling, although I did not try 50%.... The Yield Strength was in between what it was when this PLA was printed at 100% cooling at 220 and 230 deg.... so yes, you can increase the strength of PLA by reducing the cooling, but only if you are printing at a lower temperature than what gives the strongest print at 100% cooling.... This makes perfect sense, and may have some applications, where your appearance (particularly stringing) is suffering if you print at too high a (cosmetic) temperature to get the highest strength.... I realize that this is a data set of "one", but I won't be testing different cooling settings on a regular basis....
The first PETG tests are on the printer, so stand by!....
Bob
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Good stuff, Bob. I never tried this test, but your conclusion makes sense. Printing "too hot" for best strength can cause more oozing and dripping, too, so great to know less temp, with less fan can give similar strength.
On my Ender 3, the cooling fan is showing its age -- it will not spinup by itself with any command under 30-35% -- I don't know if yours has or will suffer the same fate, but the 0% and 20% being almost identical made me remember that tidbit.
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Bob,
Surely the shallower the helix angle (finer pitch), the more mechanical advantage a thread has? Therefore clamping force should go up with a finer pitch at a given diameter. Yes, friction eats up a lot of clamping force, but if you think of the thread as a spiral cam, the helix angle seems to matter; a lot.
The calculator seems to use "half angle", rather than pitch.
https://www.engineersedge.com/calculators/bolt_torque_from_thread_pitch_calculator_15830.htm
https://securitylocknut.com/how-is-clamp-force-for-a-bolt-and-nut-assembly-calculated/
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I thought exactly the same, but just as the finer pitch moves less per turn, stretching the bolt less per revolution, it is also easier to turn.... A coarser pitch will reach a given "torque" sooner, which balances out the increased stretch of the bolt....
I looked at those calculators you linked, and the first doesn't have pitch as an input (a 60 deg. thread has a 30 deg. "half angle").... and the second one is for calculating the maximum clamping force, based on the grade of the bolt and the pitch (which affects the shear area).... If you can find an axial force calculator where the pitch makes a difference, I'm sure "Engineers Edge", which is where I linked, would be most interested.... Here is a link to the equations that calculator is based on....
https://www.engineersedge.com/torque.htm
Bob
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I will take another look, Bob
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Really, REALLY Counterintuitive.... ???
Bob
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sub, here is a possibility for a test block....
(https://hosting.photobucket.com/images/oo221/rsterne/Thread_Test_Block.png) (https://hosting.photobucket.com/images/oo221/rsterne/Thread_Test_Block.png)
It is a 1" square, 1.75" long, with 1/2"-20 threads in one end, enlarged to 13mm diameter (but length not changed) which should be pretty close to a thread in for a 1//2"-20 bolt or rod.... The threads have a cylinder behind (above) them that is 14mm diameter, and limits the thread engagement to 12.7mm (1/2"), and gives room for the end of a tap if one is needed to clearance the threads.... Above that is a transverse 10mm hole (fits a 3/8" bolt shank), with enough material around it to be (several times) stronger than what I can pull with my setup.... If you use 100% fill, it takes just over 2 hrs. to print, so quite acceptable.... I would mill an aluminum adapter that would fit over the block, and the other end fit inside my moving slot.... If you want to try less thread engagement, just modify the print to shorten the threads by subtracting material from the outside, easy peasy....
Bob
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Brilliant, Bob!
With that much wall thickness around the thread the fact that the wall thickness varies is academic. But one might round the outside of the section that has the cylindrical hole to make the wall even.
Rather talk about it, I went ahead and designed three test piece, based on your template:
1. One intended to be ready for use, straight off the printer (might benefit from de-fuzzing with a tap).
2. One intended to be chased with a tap before it can be used.
3. One that is blank hole for tapping, with its ID equal to the minor diameter of the for chasing version.
I designed the parts to be self supporting when printed upright, so the threads are facing the platen.
I took the opportunity to reduce print time, by removing material from the rectangular part.
To reduce thread engagement, either don't screw the bolt all the way through the exactly 1/2" deep threaded section; or trim the STL in the slicer, by "sinking" it below the platen level so that a specific number of threads are left. The latter option would have a different thread termination than the 45 degree chamfer at both ends of the full threaded section.
Screwing in the bolt by 10 threads (1/2") and then backing it out by so many turns should be easy enough. Else, I can make shorter test print files with the same thread termination as these ones.
All three files are attached in one ZIP file. See Images below comparing the three test files.
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Yep, those should work fine.... My model doesn't have the 45 deg. taper at the outside of the threaded hole, as I downloaded the McMaster-Carr file for a 1" long threaded rod, and "chopped" off both ends, then increased the diameter to 13mm (but left the length alone, of course).... Here is the file for mine.... Printing with smaller layers will reproduce the thread profile better, because of better resolution, of course.... maybe the strength too?....
BTW, on my "Z" coupons, when I rounded off the end, they broke through the sides of the eye, when I went back to square (with the same margin of material), they no longer broke.... It must be something to do with the loading from where the bolt pulls on the coupon being spread out by the layers over the entire end of the coupon when squared off.... That is why I left mine square, and didn't worry about the extra material....
Bob
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I'm curious how you are going to test these.
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I will make aluminum adapters to connect the printed test block to my existing setup....
Yesterday and today I ran the tests on Overture PETG Gray.... I did both the Horizontal (X) Coupons and the Vertical (Z) coupons.... I used both the thin and thick ended horizontal coupons, and found so little variation in the results that in future I will only use the ones that at 4mm thick throughout, as they print a bit faster.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Overture_PETG_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Overture_PETG_Temp.jpg)
The vertical coupon showed a greater response to temperature change than the horizontal one, which varied only a small amount with nozzle temperature.... However, both were the strongest at a nozzle temperature of 240*C.... The bed was at 80*C, and the cooling at 60% for all tests.... All the vertical coupons broke suddenly near one end of the 5.6mm x 4.8mm test section, where the 45 deg. taper started.... All the horizontal coupons yielded at the psi's given in the graph above, but all of them (both thick and thin) continued to stretch in the area of failure for 30 sec. more, at which point I stopped the test.... They all yielded and stretched somewhere in the middle of the 5.6mm x 4mm test section.... The PETG is about 78% of the Yield Strength of the Overture PLA, but once it yields, it resists breaking immediately.... I now have a standardized test which I will use in the future, unless some filaments (such as Carbon Fibre filled) exceed the capabilities of my setup with the horizontal coupons, in which case I will thin up the test section....
Next up will be Wood PLA, and I have to go back and test the vertical coupons with the Overture PLA… It takes about 2 hrs. to print one each horizontal and vertical coupons, and another half hour to break them and record the data, times the number of temperatures I test (about 6)… Realistically, that works out to 2 days for each material, and uses about 100 grams of material (about 33 metres) to run one set of tests (assuming no failures)…
Bob
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Thanks, Bob
Interesting that the rounded test samples broke. I will take the round top features off the ones I designed.
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Same files as before, but V2 indicates square tops.
3 STLs in zip file.
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The rounded tops probably have more strength than my test setup can stand.... just though I would mention it....
When I get a chance, I will machine up an adapter for a 1" square bar, and make an adapter for the other end to a 1/2"-20 male thread....
Bob
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Thanks, Bob
As always, you are free to use whichever arrangement makes most sense to you.
I generated the CAD designs for fun. Using any of them is optional.
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I wonder if I should put the axis of the second set of 3/8" pins at 90 deg. to my current setup (ie horizontal)?.... It would make kind of a universal joint, free to rotate in both planes?.... Any advantages/disadvantages?.... For a disadvantage, I guess they could fall out, currently gravity is my friend.... ::)
Bob
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If there is any lack of alignment in the cross axis, the a universal joint seems to make sense. Using a bolt that is not fully threaded would allow one to place a nut on the other end, so nothing drops off.
A 3/8" pin with a cotter pin hole near the other end could do the same thing; if it is a problem. If you testbed is horizontal, then the test sample and support hardware might be able to lay on the testbed, rather than coming apart. If the axis lifts the parts slightly under load, there should be be any added friction.
If the test pull axis is vertical, I think the universal joint idea might sometimes move to a position where one of the pins is tempted to drop out. A partial wrap of masking tape might be enough to prevent that, if cotter pins are not a good idea.
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Pic of my setup is in Reply #7.... Pins are made from shortened 3/8" shouldered bolts, and drop in from the top.... Sure saves time over putting on nuts!....
Bob
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It helps tp look at post#7 again. From that, I don't think cross bolts to form a U-joint will fall out.
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Bob, I think if you want to limit the loads on the leadscrew, relocating the pivot point off of the cross slide to either the fixed side or in between, will limit the load onto the leadscrew to what comes through your force gage. You will need to make an extra bar though.
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Yes, if I move the pivot on the moving bar so that it is fixed (relative to the existing fixed end), and simply have the carriage move the force gauge, you are correct.... Not sure what you mean by "in between".... However, the bar will tilt by the multiple of the leverage, so if the coupon gets 5mm longer, at 4:1, the end the gauge is mounted to will move 20mm, and therefore be many degrees out of square, which could affect the measurement.... Right now, there is no angle change at all.... 8)
It might be a good design for measuring thread strength, however.... but realistically, for a threaded connection, isn't the maximum torque you can apply before failure more important?....
Bob
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OK, so yesterday and today I ran some iSanmate Wood PLA+ that I had, and the 20% wood filler certainly weakened it.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/iSanmate_Wood_PLA_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/iSanmate_Wood_PLA_Temp.jpg)
Interestingly, the minimum temperature recommended on the reel of 190C produced the strongest horizontal (X) coupon, but at that temperature the layers were not at all bonded well, and the vertical coupon failed at only 1260 psi, and when it did, it failed in two spots!.... The strongest layer bonding occurred at about 210C, and at that temperature this Wood PLA+ was less than half the strength of Overture PLA.... It's great for appearance (but strings at over 210C anyways), but not very strong....
Bob
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Not suggesting you change your current test approach. It sounded like you and Subscriber were coming up with a coupon for 1/2 inch thread that might impose high loads on your lathe.
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realistically, for a threaded connection, isn't the maximum torque you can apply before failure more important?....
Not for the applications I have in mind: A 1 to 2" OD cylinder is screwed onto the barrel muzzle by hand, until it is tight enough to square up on the mounting shoulder, and not move or loosen during the shot cycle - or after multiple shot cycles. Tighter than that just uses up thread strength, that would otherwise prevent the "cylinder" from blowing off.
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Stan,
We certainly do not want to risk damage to Bob's lathe.
I suspect that for decent prints, the thread strength will be enough. So, if a typical depth of 1/2-20 thread can stand 400 lb, then I would consider that a proof test.
A typical thread depth is 10 to 13 mm based on barrel stud lengths I have seen recently. To predict the failure load for a 1/2" thread depth or 10 mm for that matter, reducing the engagement to 1/4" or 5 mm and then testing to thread failure would be very reasonable. If 1/4" or 5 mm thread engagement exceeds 400 lb, then use 1/8" or 2.5 mm thread engagement, until the test part fails.
If we have to rely on too few threads to avoid exceeding 400 lb, then the test repeatability may become poor. Then perhaps using a full 1/2" or 10 mm long thread would be better, but the thread form would be configured to be shallower to reduce it strength that way. The exact plan can be refined, based on early results.
How much force does a muffler apply to the barrel stud during firing? One way of measuring that indirectly is to design a series of short test mufflers that have thread depths at 10, 5, 2.5 and 1.25 mm, or equivalent inch measurements, starting at 0.5". These mufflers would be test fired in turn until the thread stripped and the muffler flew off. Or, a similar series of muffler where the thread axial depth was kept at 10 mm (or 0.5"), and the thread form reduced for less engagement, till the muffler blows off.
These blow off test results could be correlated with Bob's pull force measurements. So we know what we need; and what we got.
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Yes, Stan, thanks for that.... I certainly would not want to overstress the lead screw thrust bearings.... or the vertical support that holds the fixed end now....
sub, if I get the time I'll try and get the adapters done in the next week or so.... I would start with 3 threads (0.150") of engagement and see how close that gets to (or exceeds) 400 lbs.... I assume PETG?.... Has anyone done any checking into the hoop stress of said muffler.... Having one grenade would not be desireable.... :o
BTW, I have read that increasing the number of walls until the object is solid (and using no infill) produces the strongest prints.... That is what I am doing on my test coupons, the walls touch throughout the (horizontal) test section....I would think that using the round threaded portion would be an excellent candidate for that approach, it would take about 9 walls (@ 0.4mm) to do that....
Bob
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Just doing a strength calculation on the round section.... It will be printed in "Z", so the layers will be trying to pull apart.... The area between the recess ID (14mm) and the OD (25.4mm) is PI (25.4^2 - 14^2) / 4 = 353 mm^2 = 0.54in^2.... My PETG "Z" Coupons fail at ~3600 psi, best case (240C), so that should be good for (0.54 x 3600) = 1944 lbf, or almost a ton.... In theory, over a 4:1 safety margin higher than what I will pull on my setup.... So, a 1" OD it will be!....
Bob
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Sounds good to me, Bob
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I downloaded the square top .zip file.... I see you have 45 deg. chamfers top and bottom of the thread.... How many "good" threads do you have in the "use as is"?.... If I drop it below the platen to shorten the threads, that chamfer makes it difficult to know what I get.... BTW, printing time, all walls in the threaded section, is 2 hrs. 1 min.... I'm thinking we should just have straight thread, no chamfers, with 10 threads (1/2") total.... What are you using for the OD of the "use as is" threads?....
Bob
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Bob,
I removed the chamfers from both ends of the threaded sections, on all three test pieces.
CAD Dimensions:
The threaded sections are 12.7 mm long
The thread root diameter is 13 mm
The unthreaded cylindrical section is 14 mm in diameter
Three STLs in attached ZIP file
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OK, so yesterday and today I ran some iSanmate Wood PLA+ that I had, and the 20% wood filler certainly weakened it.... Here are the results....
Interestingly, the minimum temperature recommended on the reel of 190C produced the strongest horizontal (X) coupon, but at that temperature the layers were not at all bonded well, and the vertical coupon failed at only 1260 psi, and when it did, it failed in two spots!.... The strongest layer bonding occurred at about 210C, and at that temperature this Wood PLA+ was less than half the strength of Overture PLA.... It's great for appearance (but strings at over 210C anyways), but not very strong....
Wood filaments are notorious for being more for looks than durability. Some of them have real wood, and will darken more or less depending on temperature, and how burnt the wood gets. I remember reading about someone who post-processed the gcode file to pseudo-randomly change the temperature, within a specified range, to simulate "wood grain." The prints will kinda-sorta take stain, too.
Tests like these are great -- some filament vendors seem to cut-and-paste the same temperature range on all their similar products, without even testing, apparently. Trust, but verify.
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I will test any filaments that anyone wishes to send me.... I need a minimum of 100 grams (33 metres) of filament, assuming no failures, and it takes me a couple of days to run the tests in both the X and Z axis.... If you have half/part rolls you wish to donate, I'll run them for you and publish the results here....
Bob
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Bob,
I don't have partial roles to donate, because I don't have full rolls. Being as I like to watch people who know more about printing do their thing. But, I get that expecting you to buy a lot of material to amuse us, is not as much fun for you. So, the only way I can send you material is to have it shipped directly to you, via amazon or your preferred source.
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If the motivation for the 1/2-20 tests is the pressure in an LDC, perhaps that can be explored. Instrumenting the LDC with a pressure gage or strain gage would be great but would take some resources. What about a sacrificial wall section in a special test LDC. The image show the basic configuration. The top section would continue on with the rest of the LDC features. If a one wall (~.4mm) thickness stays intact, one could castle it and tape the insides to seal. Once a configuration fails, it could be compared to a pull test.
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Stan,
I think that making test LDC with thin section to see what they can stand has merits that go beyond correlating back to thread strength. Stain gauge readings could be interesting.
The problem with LDCs (or the first expansion chamber in particular) is that they are not a known closed volume, that can be relied on to reach a calculated pressure, when a barrel full of air at a known pressure dumped into them. The bore is a massive leak, so pressure does not build up like a closed vessel. On the other hand the way the air enters the LDC is more like a car crash than using the brakes.
Again, any clever ideas we can come up with for test purposes would enable lighter LDCs to be designed, so they have enough strength where they need it, and no extra material where they do not.
All that said, if the first baffle has an effective area of only 1 square inch, then if the residual bulk pressure is 200 PSI after expanding into that chamber, the baffle sees a very rapidly applied 200 lb trying to rip that baffle forwards, off from the base. Providing the structure survives, I think it is the flow resistance out of the bore that is trying to rip the LDC off the threads. Because a closed pressurized container would have all the the fore/aft forces balanced in the walls, with no pull on the threads. Then there is the radial burst pressure that is superimposed on the axial forces...
I have suggested some single known expansion chamber volume LDCs, with a pin hole vent, dry fired to see what wall thickness is required to stand that. That idea was not immediately popular with the other Bob posting in this thread. A proposal the other Bob made and already implemented was an Avenger LDC inserts where the section ahead of the shroud had a 1 mm wall. Another with 0.5 mm wall was also tested. These were surprisingly robust; but, those sections had the benefit of the reflex expansion volume in the Avenger shroud, and over 3" of shroud ahead of the muzzle to drop the bulk pressure.
Keep the ideas coming; although I think Bob's thread should be more about tensile testing samples, strategies and results. Even though my thread testing interest is obviously linked to retaining LDCs.
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I think Bob was going to make some custom tooling for the thread pull test. If he has not done so already, perhaps the test can be simplified to a double sided pull just using cut down bolts or all-thread for the tooling.
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Muzzle pressures can vary from a few hundred psi to nearly full tank pressure, if the reservoir is large and the dwell longer than the time the projectile stays in the barrel.... The volume of the barrel can vary from 5cc for a 12" .177 barrel to 116cc for a 36" of .50 cal.... If we look at a .25 cal 25" barrel, the volume is 20 cc, and I doubt the first chamber in most LDCs is larger than that.... If you have a 200 cc reservoir filled to 3000 psi, and the valve is still open when the projectile exits the muzzle, the residual muzzle pressure is (3000 x 200 / (200+20)) = 2700 psi, and with an equal volume LDC chamber, that would drop to (3000 x 200 / (200+40)) = 2400 psi.... Think about that when you pull the trigger with a 3D printed LDC....
Now I realize you probably won't be running an LDC on a gun with maximum residual pressure, but if the valve closes when the projectile is halfway to the muzzle (10 cc of barrel volume) the residual muzzle pressure is (3000 x 10 / 20) = 1500 psi, and with a 20cc LDC chamber it would be (3000 x 10 / (20+20) = 750 psi.... not insignifcant....
Stan, that is a brilliant way to simplify the problem.... Make the sleeve with 1.5" of threads, and thread one piece of rod in halfway (a full inch).... On the other end, count turns, starting from 2-3 turns.... If you never exceed 1/2" on the "test end", the other end should not affect the results enough to worry about.... and each test sleeve is disposable anyways.... 8) ::) :o ;D .... I wonder how strong the shank of a 1/2" bolt is with a 3/8" hole drilled crossways through it.... hmmmmmmm....
Bob
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I think the retaining pin can be undersized. More slop helps self alignment. I'm guessing that the shear strength of a 1/4" rod is higher than you want to apply to your lathe. ;)
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Area of bolt shank = PI/4 x (0.5^2) - (0.375^2) = 0.785 x (0.25 - 0.141) = 0.085 sq.in.... A grade 5 bolt is 92Ksi yield strength, so that is a minimum of 7872 lbf.... Should be more than enough!.... I just need some 2" or longer shouldered bolts!.... Here is a design, 25 x 25 x 40mm with 13mm (1/2-20) threads.... All walls, prints in 1 hr. 12 min....
(https://hosting.photobucket.com/images/oo221/rsterne/Half20_Test_Cylinder.png) (https://hosting.photobucket.com/images/oo221/rsterne/Half20_Test_Cylinder.png)
The .stl file is below.... I'll just drill a couple of 1/2-20 bolts and machine the shanks flat to thickness to fit my setup....
Bob
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What is good about Stan's simplified thread specimen is that one will have two data points in one test piece. The load at failure, and what the thread looks like the end that did not fail, but that took the same load. I am assuming only one side will fail, most of the time, like a wishbone.
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Bob,
It is good to do basic volume/pressure exchange calculations as a reality check for LDC designs. I have a spread sheet set up to do those for me, but confess I only used it when the airgun FPE is over 60 FPE for rifle length barrels. I used the calculator recently for the Huben pistol mufflers I designed. That has a very high muzzle pressure because of its short barrel and high FPE. It also has a propensity for the valve to stick open, if you shoot until the reservoir pressure drops too low.
I certainly prefer using an aluminum or CF tube for anything over 50 FPE. But have fully printed designs for the Huben pistol where most walls are just 2 mm thick. I had help testing conditions that emulate a stuck valve with a short barrel. Shall we just say that my printed Huben pistol mufflers are not rated for stuck valves. To do that would require walls perhaps 3 or 4 times as thick. It would be so heavy and expensive that no one would want one. And I make that clear to anyone that wants to use one. I am happy to report that should such a long valve duration event occur, no bits are projected towards the person holding the airgun. This is based on more than one data point in controlled trials, rather than customer hands. Also, the mounting threads do not appear to be a weak link in the chain. Assuming they are printed properly, rather than with a overly shallow thread form.
Commercial mufflers are not made as string as the air tanks that feed them. So, while a lot stronger than thin poorly printed plastic, some commercial might not be able to contain a stuck open valve event. One might even argue that coming apart at 500 PSI is better than coming apart at 3000 PSI, due to the severity of the event. It was suggested to design in what amounts to a hinged flap in the first expansion chamber. Something that would open a relief air path, but not create a free fragment that might go somewhere unexpected. A fail safe, if you will.
My muffler designs tend to get larger in proportion with FPE, and the first expansion chamber with it. Larger for backyard friendly than hearing safe.What I really would like to know, is how much the peak air pressure in the first chamber drops, due to the flow out of the baffle bore. What I can tell you is that I design my baffle bores with generous projectile clearance, so that extra flow relief should help. The loss in muffling performance is not as much as one might estimate when oversized bores are used. Take the Marauder for example. The stock baffles are the same for .177, .22 and .25; using 5/16" bores for all of them. None of them are loud at typical power levels for caliber.
Anyway, back to thread testing...
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I got a chance to go back and test the Vertical (Z) coupons with Overture PLA this evening, and plotted them along with the previous Horizontal (X) curve.... Here they are....
(https://hosting.photobucket.com/images/oo221/rsterne/Overture_PLA_Both_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Overture_PLA_Both_Temp.jpg)
The vertical Yield strength peaks at 220C, instead of the 230C for the horizontal Yield.... at about 57% of that for the horizontal at 220C.... I am extremely pleased with the consistency of results I am getting with my coupons.... Based on these results, I will be printing the thread sleeves at 220 for the PLA and 240 for the PETG (both Overture).... I think I will do 5 or 6 of each, so that I can test various thread depths....
Bob
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That 2:1 strength differential is very telling. I wonder how that compares to wood, along and across the grain? Of course, there are many types of wood, and it varies a lot within one type.
If plywood is a good structural material, is it possible to 3D print an interweave of horizontal and vertical printing. My gut says no.
Perhaps printing the pull test coupons at 45 degrees off horizontal is the best way to produce more even strength? Assuming that a given part needs even strength.
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I have seen threads printed on a 45 deg. angle, and they end up in between vertical and horizontal.... Using a line or zig-zag infill is about as close to plywood as you can get, right?....
I am printing five PLA thread test cylinders right now.... I changed the design, separating the long and short threads with a 14mm cylinder....
(https://hosting.photobucket.com/images/oo221/rsterne/Screenshot_2023-11-05_102310.png) (https://hosting.photobucket.com/images/oo221/rsterne/Screenshot_2023-11-05_102310.png)
The long, upper portion has a 45 deg. taper at the top, the other three ends of the threads are square, no countersink.... The upper section is 25mm long, the cylinder 5mm, and the lower section 10mm, for a total length of 40mm, and a diameter of 26mm (increased a bit to give a full 6mm wall around the 14mm diameter center cylinder.... I have put 5 models into Cura, and set 4 of them below the Platen by 2, 4, 6 and 8 mm, giving me coupons with 2, 4, 6, 8 and 10mm of test thread.... This will give me an engagement depth to work with, and then I will try different layer heights.... Just over 6 hrs. to print all five.... 8)
I still have to get and machine the end bolts....
Bob
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Crisscross 100% infill is like plywood in the X and Y axis, but it does not improve the Z-axis layer to layer adhesion. It was the Z-axis plywood I was aiming for. Unobtanium, unless you glued more that one part together. At least I can't think of a way to print it, but I am not a printer expert.
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Well, today was an interesting, wasteful, but eventually productive day....
I started up the five threaded cylinders in PLA that I mentioned above in Reply #83, and then went out to the shop to hopefully make the 1/2"-20 threaded adapters to fit them to my testing setup.... I had some Grade 8 bolts the right length, so I tried milling flats on the side, and after making a shallow initial cut, my HSS mill just polished the surface and wouldn't cut any deeper.... I didn't have anything of less quality, but I did have some coarse threaded rod, and it milled fine (with the same mill, fortunately I didn't cook it).... This week I will pick up some fine thread rod (hopefully they will have it in town), barring that I will try and get some "hardware store quality" bolts.... I have decided to use 5/16" pins, and to thin the bolt by milling flats to insure it will pull closer to the center, and not tilt the test pieces....
Anyways, back to take the finished prints off the printer, and the outside was fine, but the threads were a real mess.... I had forgotten to print outer walls last, and to use the "Exclusive" setting for the slicing of the sloped surfaces of the threads.... plus I only printed at 0.2mm layer height.... There were strands of filament running from point to point inside the threads, from say 2 to 4 o'clock, then 3 to 5 o'clock, etc. as each layer printed.... Not all layers were like that, but the inside was sure a mess.... I ran a tap through them, and it cleaned them up OK, but there were chunks missing from the threads, like it had been machined with a dull tap....
Anyway, I decided that the 2mm (which is just over 1.5 theads) was a joke, and the 10mm was likely too strong, so I repeated the printing, still in PLA, with a 0.12mm layer height, exclusive on the profile setting, and outer walls last (which makes overhangs a lot better, so really improves the thread profile).... Printing time stayed at just over 6 hrs, but for only 3 instead of 5.... They turned out beautiful, and a bolt threads in by hand with no cleaning with a tap required.... So, once I get the threaded rod and make my ends, I will have 4, 6 and 8mm sections of thread to test.... If they all work, I will have a 3-point graph of pull-out force vs thread count.... Wouldn't that be nice?....
Bob
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Bob,
Your hassle with thread printing and your solution make me not even want to try it :)
I rely heavily on the other Bob to print threaded parts I design. He has it all figured out. At this point, the prospect of learning the software settings to make a printer run right, makes me feel more like a mechanic than an electrician. You seem to have mastered all this trickery rather fast.
Good to hear about success after you got the kinks out of the way. It sounds like that grade 8 bolt was springing your mill. Assume the HSS cutter did not get dulled.
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Interesting to hear of printing thread issues. Can't say that I have experienced any issues printing 1/2-20 threads in PETG at 0.2mm height with nominal PrusaSlicer settings. Not much stringing, relatively well formed threads. A tap only removes the tiniest amount of fuzz. Maybe I was lucky? Anyways, I chuck the LDC in the lathe and use the tail stock to center the tap, line up the threads and turn the tap by hand. It takes little effort to go through, since the threads are only the slightest bit undersized. Since tapping takes so little time compared to constantly reprinting coupons, I haven't bothered to refine the threads anymore.
I am encouraged by Bob's tests, they should reveal things of interest for the airgun community.
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Bruce, I think the biggest issue was printing outside to inside, as the protruding edge of the thread profile has nothing to sit on, and ends up as a straight line from where it has no support to where it touches again.... When you print inside to outside, the last part of the thread to be printed is the overhanging tip of the profile, and it has something to at least stick to, if not sit on.... By using a thinner layer, but the same wall thickness, the "next" layer printed is a more flattened oval, and has a significant overlap to sit on, and I don't get the stringing.... It was just a matter of not changing the settings back after printing my tensile test coupons, where I had it printing outer wall first to get more accurate and consistent dimension on the thin test section....
I am thinking I have way too much wall thickness, and I will probably print some today with smaller OD's to speed up the printing process.... I'll try a 20mm, and if that fails, go to 22mm, etc.... Currently I am at 26mm (full 6mm walls at the 14mm cylindrical thread break)....
Bob
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Well, I machined up the adapters today.... I annealed the Grade 8 bolts by heating the shank and head to cherry and letting it cool slowly.... I was STILL having problems with the mill not cutting.... I found out that 0.020" was not deep enough cuts, and when I went to 0.030" cuts, it worked fine.... So, once I had the adapters done (and 5/16" quick pins), I put the 2mm of 1/2"-20 thread sample in and it took 51.0 x 4 = 204 lbf. to break it!.... :o
I then tried a 4mm thread sample, and I stopped pulling at 110 x 4 = 440 lbs. (200 kg.), which is the limit of my force gauge.... One thread is 0.050" = 1.27mm, so the number of threads was 4 / 1.27 = 3.15 threads!.... Now we know that three 1/2"-20 threads in PLA will stand over 400 lbs!.... I am SHOCKED, that is over 100 lbf. per mm of engagement!.... Here are the samples and an assembled test piece (with only a 20mm OD, plenty strong enough)....
(https://hosting.photobucket.com/images/oo221/rsterne/Half_20_Threads.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Half_20_Threads.JPG)
Top left is the 2mm sample after failing.... Center is the 4mm sample, and it looks a bit beat up, but that was what it looked like after I chased the threads, which were done at 0.20mm layer height.... Right is the 0.12mm layer height sample, which has also been subjected to 200 kg. of pull, and it looks and screws onto a bolt like new.... NO permanent damage....
I'll print up a few thin engagement samples in PETG to test, but all the rest of the samples I made are too much thread engagement for my setup!....
Bob
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Amazingly strong!
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Great results Bob.
If you want to try higher loads, Using some longer bars (1" square tubing?), still connected to your lathe and load cell, could get you higher gain without overloading your set up.
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Stan, while that would certainly work, do you really think we need more information?.... I'll test some PETG, which I expect to be weaker, and I'll probably print samples at 2, 3 and 4 mm for that, with the 20mm OD.... They won't take long to print, I can do them all at the same time by setting them below the Platen....
Sub, anything more you would suggest?....
Bob
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No, I think you captured the data relevant to the airgun application.
I just thought, since you printed them, if you Really wanted to brake them, then there might be a simple configuration.
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I have redesigned my thread test cylinder to 20mm OD, 25mm tall, with a 4 thread high (5.08mm) test section.... I will be printing 1, 2, 3 and 4 threads in PLA and PETG, using a layer height of 0.158mm, which gives exactly 8 layers per thread....
(https://hosting.photobucket.com/images/oo221/rsterne/Screenshot_2023-11-08_084818.png) (https://hosting.photobucket.com/images/oo221/rsterne/Screenshot_2023-11-08_084818.png)
The printing time is just over 2 hrs. for 4 cylinders, 1 of each length.... The object is to produce a strength graph for each filament, with force to fail plotted vs number of 1/2"-20 threads.... It should be a straight line, of course.... If I need more data points, I will do test cylinders at 1.5, and 2.5mm of threads....
Bob
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Bob,
Do you print one test piece at a time; or four of them together? I assume that printing one at a time will be stronger because the welding of subsequent layers will occur at higher temperature - less cooling time between layers, if the part is effectively smaller with no jumps between parts.
Perhaps this effect would be small for four 20 mm tubes that are almost touching on the platen?
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I print several at a time, different lengths by setting them different depths below the platen.... I did 5 for the PLA (1, 1.5, 2, 2.5 and 3 threads), and for the PETG I will do 7, adding 3.5 and 4 threads.... The PLA printed great, I am having some stringing with the PETG, so I'm currently running some test towers to hopefully refine the tune.... It may be time for a new nozzle....
I just read that with PETG, for cosmetics you should run 60-100% fan, but for more strength 30-50%.... Anyone care to comment?....
Bob
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Default settings in PrusaSlicer for PETG is 30-50% fan speed. Fan disabled for first 3 layers. Seems to work for me.
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I just read that with PETG, for cosmetics you should run 60-100% fan, but for more strength 30-50%.... Anyone care to comment?....
Bob
I used to run the low-to-mid fan since it was on in the defaults, and recommended for dimensional accuracy, but lately I run no fan, and have not noticed any loss of cosmetic appeal or sizing. I think you just showed that less fan doesn't always mean more strength. It sort of makes sense the faster it cools, the less time it has to ooze, though. The more I read online articles from websites that should know, and anecdotal results from individual users...the less I trust the websites that should know. Too many variables involved, too many formulations of PETG filament, for blanket recommendations like that fan speed one to necessarily hold true.
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I ran a set of thread tests today, 1/2"-20 threads printed at a layer height of 0.158mm (8 layers per thread) in both PLA (Overture Grey) and PETG (Overture Black).... I tested 1, 1.5, 2, 2.5 and 3 threads in PLA and those plus 3.5 and 4 threads in PETG.... I could not test more in the PLA because it would have exceeded the limits of my Force Gauge.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Thread_Strength_Half-20.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Thread_Strength_Half-20.jpg)
The PLA took about 150 lbf. per thread to break, and the PETG took about 80 lbf. per thread.... A single thread is not very reliable for data, as one might expect, but from 1.5 threads up, the data is pretty linear, as you would expect.... The dotted lines give the Shear Strength in psi, based on the calculated theoretical area of threads in shear (number of threads x pitch diameter x PI x (pitch/2)).... The last number is the theoretical thickness in shear of one thread at the pitch diameter.... For 1/2"-20TPI that works out to 0.0368 sq.in. per thread in shear.... In theory, those should be straight, horizontal lines (the shear strength should be constant, independant of area).... They are pretty close, so that validates the testing method....
I took photos of the broken test cylinders, and the results were interesting.... First the PLA....
(https://hosting.photobucket.com/images/oo221/rsterne/PLA_Threads.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/PLA_Threads.JPG)
and then the PETG.... Both photos had a single thread on the left, increasing in thread count to the right.... Click on the pics to enlarge....
(https://hosting.photobucket.com/images/oo221/rsterne/PETG_Threads.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/PETG_Threads.JPG)
In all cases, other than the very thin thread samples, the failures occurred right where the last thread stopped, where a 14mm diameter internal cylinder provides a precise location where that occurs.... The test threads were between that 14mm ID and the outer end of the test samples.... Now one might think that showed that the wall of the cylinder at the 14mm diameter was too thin, causing the part to fracture there.... In fact, with the PETG I made the OD larger as the thread count increased to help avoid that, to no avail....
I went back and checked my calculations on that portion of the cylinder, and recalculated the theoretical breaking force, using my measured tensile strength in the "Z" direction for these two materials.... The area of that cylindrical portion is (20^2 - 14^2) x PI/4 = 160 mm^2 = 0.248 sq.in.... The Overture PLA had a tensile strength of 4750 psi when printed at 220C (which is what I used for the thread test), which should take (4750 x 0.248) = 1178 lbf. to break, requiring nearly 4 times as much as the 300 lbf. it took to break the middle sample, which had 2 threads.... The Overture PETG had a measured tensile strength of 3650 psi at 240C (the thread printing temperature), which would take (3650 x 0.248) =905 lbf. to break, over 9 times the 100 lbf. it took to break the 1.5 thread long sample.... Additionally, if it was the wall thickness of the 14mm ID section that was the weak point, it would have failed at the same force in every test, which it did not.... Also, the thicker cylinders I used for the longer threads in the PETG samples, would have showed an increase in force required to break them.... The largest OD samples I used were 26mm, having a cross sectional area at the 14mm ID more than double that of the 20mm cylinders....
So, how are the samples breaking?.... If you look closely at the thicker thread samples in PETG (right end) you will notice that the samples broke along a cone shape, and did not simply rip between the layers.... None of the samples (except the very thinnest ones, which stripped out) broke anywhere but at the inner end of the threads, which of course is where the stress is the highest.... Although every thread imposes load on the cylindrical wall outside of it, those loads add up and peak where the threads end at the 14mm ID recess.... Therefore, that is the point that tears first, and once that rip starts, it just zippers across the outer tube, following the line of maximum stress, which is supported less and less as each layer of the print breaks....
The fact that the data behaved exactly as it should, and that the Shear Strength was less than the Tensile Strength of the material (in the Z direction), I think these are valid and reliable tests.... How thick an outer structure would you need before you would see even 4 threads pull straight out the end?.... I dunno, but way more than the 6mm wall in those 26mm OD samples....
Bob
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OK, curiousity got the better of me, and I did one more test with a cone-shaped test piece, 50mm at the base and at 11mm up, tapering to 24mm at the top (25mm high).... It was PETG with only 3 threads, and took 340 lbf. to break.... and it broke in a way I did not expect!....
(https://hosting.photobucket.com/images/oo221/rsterne/3_PETG_Threads.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/3_PETG_Threads.JPG)
I should have known that is what would happen, comparing it to the previous test with 3 threads, which broke at 240 lbf.... They both broke in a shallow cone, with the deepest part at the bottom of the test threads, right where the tension is the greatest, and tapering up towards the end where the bolt was inserted.... In the case of the 23mm diameter cylinder (on the right), that left a tapered "washer".... In the 50mm diameter test cone, it ripped out a tapered wafer, where the OD was between 30-32mm in diameter.... The original sample, tested above, was limited by the OD, but the cone was limited only by the depth from the bottom of the threads to the end.... Having those 3 threads set down further from the end (or having more threads, so that the bottom thread was further from the end) would increase the difficulty in tearing that tapered piece out, and very likely make it larger in diameter, following more or less the same angle, which is roughly 20 degrees.... The ultimate strength was roughly proportional to the OD of the tearout.... (32 / 23) x 240 lbf. = 334 lbf. and the cone failed at 336 lbf.... Coincidence, or maybe a rule of thumb (for the same number of threads)?....
Following this logic, a 2" diameter solid (100%) print of PETG would support about 6 threads before the cone torn out would reach the OD and the strength then start dropping because the tear-out becomes affected by the OD.... That should happen at about 680 lbf., using double the 3 thread of this test piece.... Call it 100-110 lbf. per thread for PETG, but limited by the OD of the printed part splitting along that roughly 20 degree angle....
All of this has too many variables to be relied on for safe design work.... but it is VERY interesting to know that the limiting factor to thread strength is for the most part the OD of the part the threads are in.... If the part has Infill, the the diameter to where the infill starts would become important....
Bob
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Very useful data, Bob
Thanks for all your effort.
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Thread testing done, so back to testing the filaments I have available.... Today it's Anycubic Silk Silver PLA....
(https://hosting.photobucket.com/images/oo221/rsterne/Anycubic_PLA_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Anycubic_PLA_Temp.jpg)
The curves are very flat from 210-230C, and while the X-direction strength is pretty good, the layer to layer bonding is quite poor....
Bob
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Next up is Overture PLA Professional in white....
(https://hosting.photobucket.com/images/oo221/rsterne/Overture_PLA_Pro_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Overture_PLA_Pro_Temp.jpg)
In tension (X-Axis), the highest Yield measured was at 210C, but the curve was essentially flat from 210-240C.... The layer adhesion (Z-Axis) was virtually constant from 230C up to 250, which is as high as I went.... The Vertical sample was virtually identical in strength to the standard Overture PLA, and in the Horizontal direction, it was actually less.... However, all the horizontal samples stretched after the yield point, rather than breaking right away.... whereas the standard PLA broke above 240C.... The Z direction had 63% of the strength of the X direction, which is pretty good from my results so far....
Bob
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Now we get to the interesting stuff I built this setup to test!.... I ran some Polymaker PA612 Carbon Fibre today, and it did not disappoint, being about 50% stronger than the best PLA.... Here are the results.... BTW, I am using a layer height of 0.25mm for the CF-Nylons, as a 60% minimum of nozzle diameter (I'm using 0.4mm) is recommend for carbon fibre....
(https://hosting.photobucket.com/images/oo221/rsterne/Polymaker_PA612-CF_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Polymaker_PA612-CF_Temp.jpg)
The tensile strength in the horizontal (X) direction exceeded 13,000 psi.... :o .... The vertical (Z) test coupon got to 5300 psi before breaking.... All samples broke cleanly, with no noticeable stretch, as you would expect with carbon fibre.... The pieces were very stiff.... The X-direction peaked in strength at 270C, while the layer adhesion was pretty flat from 260-290C.... Within those temperatures, the lowest yield occurred at 270C, but at 5080 psi, within 5% of the 5313 max, which on data from single coupons is probably within the region of being statistically equal....
Bed adhesion was a bit tricky.... I used Garolite (FR4) which is basically printed circuit board, laminated glass fibre and epoxy.... In fact, I got a piece of copper clad one-side (and used the back), I figured the copper back couldn't hurt the heat distribution on the bed.... I used 70C, with the first layer at 80C with a nozzle temperature of 270C, and had no problems once I found that combination.... I didn't try my PEI bed, but I probably should have.... I had trouble with the retraction settings, the ones that gave the greatest strength were very stringy, and when I increased the retraction distance to clean up the prints, the outer surface was no longer smooth and the strength dropped in both axes.... Strings are not that hard to remove, so for an engineering material where strength is everything, I'll put up with them until I find a solution that doesn't lose strength....
More CF filaments to come, it will be interesting to see if price corresponds to strength!.... ???
Bob
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one variable I'd like to see tested and saves a ton of time is thicker than nozzle extrusions comparing how they would scale with the layer height to width ratio when using bigger nozzles, we know that lower LH:W ratio and so bigger nozzles are way stronger but how that plays out when simply bumping up extrusions to 125%?
aside from printing faster since you print less walls the Z adhesion would improve due to this extra 25% squishing
that's a setting I've been using for some time and doesn't affect surface quality at 125%
e.g I'm using a 0.6 nozzle and that comes out to 0.8mm extrusions by itself faster but in case strength scales up like with bigger nozzles that means you can use higher LHs too like 0.4 and that almost doubles print speed without sacrificing strength or messing with the hotend
ref:
https://www.cnckitchen.com/blog/the-influence-of-layer-height-on-the-strength-of-fdm-3d-prints
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I'm a bit confused.... You say you are using layer heights of 125% of the nozzle diameter (eg. a 0.5mm LH with a 0.4mm D).... Yet the text with Stefan's video (and the chart) show a significant loss of strength when the layer exceeds 50% of the diameter (eg.0.2mm with a 0.4mm nozzle).... I haven't watched the video yet, just read his text....
Bob
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Interesting results -- the CF-Nylon excels in XY, but is barely stronger than PLA in the Z.
At first I thought your 60% minimum of nozzle diameter was a typo, but sure enough I can't find where anyone suggests less than 50%, or less than 0.20mm layers. 60%/0.25mm minimum seems to be the consensus. One source also recommended staying under 80% of nozzle width.
This follows with Baco's great suggestion about layer height vs. linewidth (as opposed to nozzle width.) Whenever I see these percent of nozzle width recommendations, I think they should be saying percent of line width. Not everyone with a 0.40 nozzle prints at 0.40 linewidth. In fact, I have read in more than one place, that the filament naturally spreads beyond the nozzle orifice, and printing lines at ~10% larger than the orifice should be closer to what naturally wants to happen. So most should be printing at 0.44mm, not 0.40mm. I routinely did 0.50mm lines with a 0.40mm nozzle.
And good results can be had going way past that -- I've taken a 0.40 nozzle up to 0.80mm (with 0.40mm layer height.) No strength testing was done, but the parts were quite functional. It's not ideal to push that much plastic through the tiny orifice, but it can be done. Most nozzles are flat on the bottom, with a tiny hole, so as long as your linewidth doesn't exceed the width of that flat, it should get squished quite nicely.
Printing lines thinner than the nozzle size can be done to some degree, but generally not recommended.
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I'm a bit confused.... You say you are using layer heights of 125% of the nozzle diameter (eg. a 0.5mm LH with a 0.4mm D).... Yet the text with Stefan's video (and the chart) show a significant loss of strength when the layer exceeds 50% of the diameter (eg.0.2mm with a 0.4mm nozzle).... I haven't watched the video yet, just read his text....
Bob
sorry had a strong headache then, i see now my comment was ambiguous...
like Torquemaster said by extrusions i meant layer width and actually 133% the nozzle width without losing visual quality
THEN assuming that strength scales proportionally with LW one could bump up LH to go with it and print functional parts in roughly half the time
edit: interesting that the overture PLA did better above the brand's recommended temp
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In my experience so far, most filaments reach highest strength above the temperature where the prints look nice!.... Stringing is a signficant problem at the higher temperatures....
The 3DXTech PA6-CF-G3 I am testing right now is being a real bear to get to stick to the bed.... I have tried 3 different beds (Garolite, PEI and the original black Creality bed), and the only one that I can get to work well is the black Creality bed at 110*C, with Elmers PVA stick.... They recommend a bed temp of 80-110C, and even 100C doesn't stick good enough.... They recommend printing at 240-270C, and at 260 the stringing is horrible, and the surface very rough.... Not at all pleased, considering the price of it!.... Yes, I did dry it, 16 hours in a food dehyrdator, that made no difference over as opened....
In theory, given a large enough part, there is no difference in the density regardless of how many ROUND strands you have, because smaller threads have more, but smaller, holes between them.... for the same reason (again in a large enough container), #12 lead shot weighs the same as buckshot.... However, our printed strands are not round, but flattened, and the more you spread out each strand, the fewer the gaps, and for a given layer thickness, those gaps should be the same size (assuming 100% flow, and that the slicing software is doing its job on that).... That should mean that wider strands should be more dense, have more contact area with the layers above and below, and therefore be stronger.... However, layer height is related to nozzle diameter, and it appears from Stefan's video that you don't want to go larger than 50% of the nozzle diameter.... Comparing larger nozzles (when printing the same relative to diameter height and width), should produce the same density (as hole size should be relative to nozzle size), and appearance should be the only loss.... In theory.... ::)
Bob
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Well, after a week of testing, I finally got good data for the 3DXTech PA6-CF-G3.... I did my best to dry the filament in our oven (4 hrs @ 90C, as recommended) and keep it dry during printing (dry box with 50 grams of silica gel), but I have no doubt a heated dry box with the filament feeding directly into the extruder might yield better layer adhesion.... I had a terrble time getting the print to stick to the bed, and finally ended up with a Garolite (FR-4) sheet, sanded with 220 grit sandpaper, and then a thin layer of Elmer's PVA glue stick at 70C.... The horizontal (X-axis) test was nearly as good as the previous CF-Nylon I tested, but the vertical (Z-axis) was much worse.... At 230C, the first layer of the horizontal print stayed behind on the print bed, and I dropped one of the vertical coupons and it broke when it hit the floor!.... The recommend temperature range is 240-270C, and I can sure vouch for not going lower!.... Anyways, here are the results I got....
(https://hosting.photobucket.com/images/oo221/rsterne/3DXTech_PA6-CF-G3_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3DXTech_PA6-CF-G3_Temp.jpg)
I had read that this product gained layer adhesion as the temperature increased, at it was indeed the best at 280C, but less than half what I got with the other CF-Nylon I tested earlier, and worse than all the better PLA's and PETG's I have tested so far.... Considering the cost (in Canada it is $86 per 500 grams), I was hugely disappointed.... The print quality was very poor, especially as I increased the temperature, starting to string badly at 260C and getting worse the hotter I went.... If the trick with this filament is to feed dry filament directly into the printer, that is beyond what I can do at the present time, and it was so fussy, I'm giving up on it....
Bob
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I tested some Anycubic standard PLA today, in Grey.... It ended up being the strongest PLA I have tested so far....
(https://hosting.photobucket.com/images/oo221/rsterne/Anycubic_PLA_Temp_uqdPjQNSid8RPsrcywXcyG.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Anycubic_PLA_Temp_uqdPjQNSid8RPsrcywXcyG.jpg)
The yield point on the Horizontal (X axis) coupon was over 9000 psi at all temperatures from 200-240C and a very flat curve.... In the Z-axis (Vertical), it peaked at nearly 6000 psi at 220C, the next best so far was the Overture PLA at 4750 psi.... At 63% of the Horizontal strength, the layer bonding of this Anycubic PLA is great performance.... I don't know if other colours are the same, of course, but the Anycubic Silk Silver I tested earlier was about 8500 in the X-axis, but only just over 2000 layer-to-layer in Z.... I presume the "Silk" additive reduces the bonding strength between layers....
Bob
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... but the Anycubic Silk Silver I tested earlier was about 8500 in the X-axis, but only just over 2000 layer-to-layer in Z.... I presume the "Silk" additive reduces the bonding strength between layers....
Bob
Your findings agree with all the anecdotal evidence I've read -- PLA "silk" filaments may have their visual appeal, but are notoriously lacking in strength. I'm actually surprised it did fairly well in the XY. Matte (PETG at least) filaments seem to suffer a similar issue compared to non-matte -- the matte additives negatively affect layer adhesion.
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i thought from reading Stephan's tests that silver was the strongest on Z axis but maybe silk silver is something else,?
edit: I've been printing suppressors in gray
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I wish I could find a filament that approached or exceeded the X-Y strength on the Z axis.... That would be very interesting!.... If you have a link, please post.... ;)
Bob
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I made a new X-axis (horizontal) coupon today, that is stronger, uses less material and prints faster.... It has a very slightly narrower test section, 4.8mm instead of 5.6mm, still at 3mm thick.... I double checked the results from the Anycubic PLA above, and the numbers are virtually identical, although one coupon at 220C actually exceeded 10,000 psi when it yielded.... the previous test was ~ 9400 psi.... That is only a 6% variation, probably within the expected accuracy of the testing.... but still, 10 Ksi for PLA is pretty stout!....
Bob
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I wish I could find a filament that approached or exceeded the X-Y strength on the Z axis.... That would be very interesting!.... If you have a link, please post.... ;)
Bob
I don't think Z>X/Y strength is possible on FDM i meant the strongest between colors tested
https://m.youtube.com/watch?v=BMSp1WDqtpI
i got it backwards, silver weakest in Z but strong on X/Y + heat deformation
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New test coupons....
(https://hosting.photobucket.com/images/oo221/rsterne/New_Coupons.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/New_Coupons.jpg)
Less material, better load distribution (so hopefully no more weird failures), no stress risers adjacent to the test section, and print faster.... Loads on both the "X-Y" and "Z" coupons (over twice the test cross sectional area of the "X-Y") are in the 50ish lb. range (in the middle of what my setup can take).... Testing shows that so far the results are unchanged....
I ran the old coupons through my FreeCAD FEM Analysis, and there is a high stress area on the inside of the holes at the sides.... I assume as the coupon starts to stretch, the wall around the hole (which extends to the middle of the side part) bends and stretches on the inside.... which sometimes causes the eye to fail straight across, at 90 deg. to the load!.... The total area there is almost 4 times the test coupon area, but according to FEM, the load is the highest there, even with the extra area.... The change to removing the triangle between the hole and test section is to change the inner wall from wrapping around the hole (and bending) to carrying the force more directly to the test area.... So far, it seems to be working, although without the extra thickness on the "Z" coupon, it still breaks.... The test section is 5.6mm thick, and if the whole coupon is that thickness (like the X-Y, which is 3mm throughout), it can still break across the hole.... However, so far I have not seen the 9mm thick one break anywhere except the middle of the test section....
Having the test section curved, so the thinnest part is right at the center is forcing them to all fail near the middle of the coupon, no more failures where the (straight) test section met the larger ends.... so I know that part is much better....
Bob
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Bob, do you mind posting the files for your new coupon design? I think I can pull them in my setup. I ordered some of the Anycubic grey PLA ($14 for the next few hr on Amazon). It would be interesting to compare.
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Here they are, separately and together.... The test area on the X-Y is 4.8mm wide by 3mm thick, and the coupon is 3mm thick throughout.... On the Z coupon it is 5.6mm wide and thick, but the coupon is 9mm thick on the ends.... They are both intended to locate on a 3/8" pin....
Bob
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I keep hoping that I will find a Carbon Fibre filament that has a greater layer-to-layer strength (Z-axis) that is closer to what can be achieved in the horizontal (filament) X-axis.... I can't afford to play with the $500/roll blends, and it seems to me that CF strands (not ground up dust) should be capable of beefing up the stiffness in a filament like PETG that is not known for it, and they are not terribly expensive.... So, I ordered a couple more brands, and today I tested the IEMAI PETG-CF.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_Temp.jpg)
It was slightly stronger in the X direction than the other PETGs I have tested, at just over 7,000 psi, but the vertical layer-to-layer bonding was the same, at about 3,700 psi.... This is weaker than PLA in both directions.... One other thing I noticed with this filament is that in line with the filaments the strength increased with lower temperatures, which I have not seen before.... I suppose it might be even stronger at 210C, but the layer bonding (which peaks at 250C) is so poor at 220C there was no point in going lower.... I have some Kimya CF-PETG on the way, hopefully one of these will be better....
I was using my new coupons to test this, after confirming that they don't influence my results, and I am very pleased with the consistency and mode of failure the provide....
Bob
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https://www.youtube.com/@CNCKitchen
This guy has done it all. A great resource for 3DP testing.
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I agree, Stefan's videos are classic.... However, he has not tested filament strength at various temperatures, which is what I am doing....
Bob
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There are some interesting discussions on the affect fan cooling has. Here is a summary.
https://3dprinterly.com/how-to-get-the-perfect-print-cooling-fan-settings/
In the embedded videos Stefan does his usual thorough job of strength testing and CHEP shows some parameters in CURA that can be used to optimize. Note the comment in Stefan's video on the Creality fan design. Also reducing fan cooling to improve strength brings geometry and ambient temperature into the mix.
I think, while there are knobs that can be tweaked for Z axis strength, establishing a specific value for strength margin calculations should be approached with caution.
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I modified my test rig to accept Bob's coupon configuration and printed a couple of checkout coupons. Unfortunately in the excitement to make the modification, I forgot about the leverage ratio in Bob's test setup. Surprisingly, the small, geared hobby motor/leadscrew was able to pull the XY coupon (PLA) to failure at 83.54 Kg. A reasonable data point but I don't think I want to load the brass leadscrew nut to those levels. On the other hand it provided a new proof load value for the setup ;D. I'll need to add some leverage.
Bob, thank you for the coupon design.
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Not sure how I missed posting it, but a week ago or so I tested Eryone CF-PETG.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Temp.jpg)
The horizontal (X-axis) strength was pretty flat regardless of temperature, but at 6000 psi max. it wasn't as strong as Overture PETG with no carbon fibre!.... The vertical (Z-axis) was also significantly weaker than the plain PETG, until the temperature got to 260C, at which point it was basically equal.... I was not impressed with the Eryone....
Yesterday and today I tested the French made Kimya PETG-CF, which is pretty pricey at $50 per 500g roll at Digitmakers.ca (it's not easy to find), which puts it in the same price range as 3DXTech's PETG-CF at $76 per 750g at the same store.... I really liked this filament, finally I am seeing the X-axis strength bump up significantly more than straight PETG, into the same range as PLA.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Kimya_PETG-CF_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Kimya_PETG-CF_Temp.jpg)
At some point I hope to test the 3DXTech offering in CF-PETG, once my wallet recovers a bit!....
OH!.... One more thing.... I took a closeup photo of the broken Z-axis coupons at various temperature, from 220-260C.... Here they are, left to right.... Click to enlarge....
(https://hosting.photobucket.com/images/oo221/rsterne/Z_Coupons_220-260C.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Z_Coupons_220-260C.JPG)
You can clearly see that at 220C the layers are distinct and separate, and the hotter you go, the more melting and fusing that occurs between the layers.... By the time you get to 260C, you really can't see the layer lines any more.... This shows why the strength in the Z-direction increases with temperature....
Bob
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It is results like this that make me very glad I am putting in the effort.... Today I tested the plain-jane version of Eryone PETG, in white.... It is a fairly translucent colour compared to other whites I have seen, so I am guessing a minimum amount of pigment.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG_Temp.jpg)
The results for the Carbon-Fibre filled version are in the previous post.... Note that the vertical (Z-axis) is almost identical.... However, the important thing is that the plain PETG version is as much as 30% stronger than the CF version in the horizontal (X-axis), where the carbon fibres are supposed to be "aligning with the extruded plastic" and therefore increasing the strength and stiffness.... Well, not in my testing it didn't.... In fact this everyday Eryone PETG is the strongest I have tested so far along the printed strands!....
Bob
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Some filaments just add CF powder for the looks and it causes a possible loss of strength, rather than adding strands of CF that should/may improve the strength. Does Eryone claim one way or the other?
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There are a number of technical papers looking at PETG-CF. They tend to get into the weeds and their data is all over the place but the SEM pictures are interesting.
Example: https://www.sciencedirect.com/science/article/pii/S0142941823000296
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Nobody claims to use CF powder, of course.... Kimya and 3DXTech claim to use milled fibres, I don't know about Overture.... I couldn't find a claim on the Eryone website, but right now you can pre-order 30 rolls at ~half price!.... ::)
Apparently they use recycled CF in most of the filament....
Bob
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I decided to run a test on the Elegoo PLA that I bought for my 4-player Chess set.... I had a bit of extra red, and here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Elegoo_PLA_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Elegoo_PLA_Temp.jpg)
I have modified the coupons yet again, reducing the hole for a 5/16" pin instead of 3/8".... as I was still getting an occasional failure through the side of the eye, where my FEM analysis said the stress was high.... I think the bending at that point as the coupon stretched was the reason, and reducing the diameter of the hole straightens out the stress lines there.... The coupons are still giving the same values, but they are even more consistent, and I have not had any more fail except right where they should....
The Elegoo was typical for the Yield strength in the XY plane, and all 5 coupons stretched in the middle after they yielded.... All the Z coupons broke cleanly right in the center.... The layer adhesion was not as good as some other PLAs, but better than the wood-filled one.... That may be a function of the colour, if I have enough of the blue, white and black left over I will test them at 220C (where the red was the strongest in the horizontal) to see if colour makes a difference....
NOTE: I tried the three other colours at 220C (the strongest temp) and found VERY little difference between them.... They were all within 10% in X and 12% in Z of the average yield strength.... In these tests, the White was the strongest in X but the weakest in Z.... If you want to be sure about your particular batch and colour of filament, testing it would be the only sure way....
Bob
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I received a sample of Duramic 3D TPU from a reader, and ran the tests on it.... twice!.... The first couple of coupons were OK, but as I got deeper into the (re-rolled) sample, it was wet, and the coupons became rough, pebbled, with a frosted appearance, and the strength dropped.... I dried the filament for 12 hours at 50-55C, and then it was fine.... Here are the results for he dried filament....
(https://hosting.photobucket.com/images/oo221/rsterne/Duramic_3D_TPU_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Duramic_3D_TPU_Temp.jpg)
There was a huge increase in strength between 220C and 225C, after which it leveled off.... At 220C, the horizontal coupons failed because the layers were separating across the coupon, particularly where they were bonded to the sides of the "eye".... At 225C and above, that did not occur, even at maximum load.... The peak strength occurred both in X and Z at 230C, and all samples had a high gloss....
Boy, does this stuff stretch!.... I increased the travel rate to 20mm/min. (from 5), and the stronger horizontal coupons stretched 170mm in 8.5 minutes before snapping.... That is to over 4 times their original length!.... Elastic materials certainly do not follow the rules, as when you take into account how small the section was (about half size in width and height), when they failed the stress was about 4 times that shown in the graph above (ie approaching 30,000 psi).... Of course that is not how you do it, but it shows why things like tennis racquet strings can stand the tension that they can, by stretching....
One thing that occurred to me was the thought that this material might be usable for transfer ports.... It recovers most of its stretch, unless you way overdo it, and it's tough!.... If the OD was contained in metal (such as the recesses in a barrel and breech) it might be possible to make custom, stand-alone transfer ports from it.... Print them vertically, so that the layers are in compression, and the outer walls are contained by the recesses, and they might work really well.... Just a thought....
Bob
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Here are the coupons from the TPU testing.... First a horizontal (X) one at 220C (wet), before and after testing.... Note the delamination, which did not occur above 225C....
(https://hosting.photobucket.com/images/oo221/rsterne/TPU_220C.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/TPU_220C.JPG)
The next is one on the torture rack, again a horizontal one....
(https://hosting.photobucket.com/images/oo221/rsterne/TPU_230C_30min.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/TPU_230C_30min.JPG)
Here are all the Coupons after testing.... The left column is horizontal (wet), second column is vertical (wet), third column is horizontal dry, right column is vertical dry....
(https://hosting.photobucket.com/images/oo221/rsterne/TPU_Coupons.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/TPU_Coupons.JPG)
The top row (L only) is at 210C, horrible finish, virtually no bonding.... Second row at 220C, third at 225C, fourth at 230C, fifth (R only) is at 235C, and the bottom row is at 240C.... Note the rough finish and stringing on the wet vertical coupon at 240C.... That is when I decided I had to dry the filament....
Bob
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I got a sample pack of Spectrum (Polish) filament, with 5 different plastics, all with a carbon fibre fill.... The first one I tested was the PLA-CF10, which as the name suggests has 10% carbon fibre content.... Here are the results, plotted vs temperature.... Printed with a 0.4mm nozzle, at 0.25mm layer height and 0.40mm line width.... pretty much standard settings for CF....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PLA-CF10_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PLA-CF10_Temp.jpg)
This material is a bit stronger than any other PLA I have tested in the horizontal (X) direction, but quite weak in the vertical (Z) direction.... The layer to layer adhesion is not great.... I was curious about how layer height and line width affected the strength, so I did some more tests.... First of all, the horizontal (X-axis) strength does not appear to change when these are varied, total variance was within 3%.... However, the layer to layer adhesion changed quite a bit.... All the tests were done with a 0.4mm nozzle at 220C.... above which the horizontal strength drops.... Here is what happens when you change the line width.... 0.40mm is 100% of nozzle diameter, 0.48mm is 120%, and 0.56mm is 140%.... The number of walls in the test section (0.56 x 0.56mm) is also given, along with the line width, in the X-axis labels....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PLA-CF10_Width.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PLA-CF10_Width.jpg)
Note that with the 0.25mm and 0.30mm layer height there is virtually no change in the yield strength in Z as you change the wall thickness.... However, with the 0.2mm layer height, increasing the wall thickness greatly improved the strength.... With this in mind, I then tried four different layer heights, again at 220C with a 0.40mm line width, and got the following results....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PLA-CF10_Layers.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PLA-CF10_Layers.jpg)
It is quite obvious that as the layer height is increased above 0.20mm, the layer to layer adhesion increases a lot.... I'm guessing this is why a 60% of nozzle diameter minimum layer height is recommended for carbon fibre filled filaments.... Possible the inclusions in the matrix from the particles requires a thicker layer for optimum strength.... One wonders if the same thing applies for wood filled, silk, or matt filaments, which tend to have weaker layer adhesion?....
Bob
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I'm curious what temperature range the vendor recommends for the PLA-CF10?
Would it make sense to do the tests at 240C, or higher, where the Z-axis strength is strongest, rather than the XY? XY is already quite strong, the Z is the weak link. Granted, that is very high for PLA, but if it still prints well, why not?
They suggest 60% or more layer height vs line width, yet the best results for Z strength were at 36% of your widest 0.56 line at 0.20 layer height. Are their recommendations based on 0.40 wide lines only? Seems like they should have a recommended minimum layer thickness value rather than percent based on your findings.
I'm also curious what happens on the tri-color chart if you go further right -- 0.64 0.72 0.80 wide? If 0.25ish continues to be the strongest layer thickness, 0.70ish (or more) is looking good for a line width...
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Spectrum only recommend 190-220 for the nozzle temperature for the PLA-CF10.... On all my testing I always go 10-20 deg. higher.... Print quality is usually pretty bad at the highest temperatures I test (so much stringing I have to clean out the holes in the vertical sample to get the pins through, and rough surfaces)....
It is my understanding that the limits for layer height are 25-75% of the nozzle diameter (some sources say 80%), so with a 0.40mm nozzle that is 0.10-0.32mm.... I have never seen a maximum width listed, but it apparently depends on the outer diameter of the nozzle tip for the absolute maximum.... I agree I should test even wider widths, but I have never seen anyone publishing data at over 140-150%, so there must be a reason for that.... Have you tried it?.... I did do some at 150% (0.60mm) which printed OK, but on the bottom layer I started seeing gaps between the lines.... Increasing the flow might cure that....
The test spools are only 250g, and I ran out before I could do any more testing.... I certainly plan to push the limits on the PETG-CF filaments to increase the Z strength, I just tested one where the X was over 10,000 psi, and as you say the layer-to-layer adhesion is definitely the limit.... I am also seeing a trend that as you get a stronger X, you get a weaker Z.... Perhaps the material becomes so rigid the stress gets more and more concentrated on the inter-layer adhesion?....
Bob
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Agreed, PLA at 240C, 20 over their recommendations, and poor print quality -- you've gone far enough. I can't really explain why XY tensile strength must go down as Z goes up -- hopefully you will find a material that upsets that trend.
I just looked something up for grins -- structural lumber, the highest grade according to what I saw, has a tensile strength around 1650psi, and compressive of 2250psi. Not that we'll be building houses out of this stuff, but interesting that when printed well, it's at least as strong, oftentimes many times stronger. Kind of puts it in the layman's perspective.
I have printed at 200% width -- I was flow testing with a 0.40 nozzle, and did 0.80 wide x 0.40 high layers. I had to print fairly slowly to not exceed my hot end's volumetric maximum -- the results were less attractive, but functional. I did not do any strength testing. There was a point where I could request say 12mm3/second, but it would only deliver 10mm3/s -- and of course quality suffers. I did "game the system" once to command 12mm3/s on a slice that really only needed 10mm3/s, and it worked, but not something I'd recommend. You're right, the line width limit would be the diameter of the flat area around the nozzle, which is usually a lot bigger than the nozzle diameter. The smart, but inconvenient, thing to do past 150% or so of nozzle size would be to put on a larger nozzle. ;)
Keeping layer height at 25-75% of line width is a good practice. I have done 0.08 on a 0.40 line/nozzle, and 0.12 on a 0.50 line/nozzle, so I've successfully been in that 20-25% zone. I rarely go over 50% with concerns of how well it will squish together, and more recently because of knowing how overhangs will suffer.
Keep on testing Bob, this is great stuff!
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Carrying on with the Spectrum Carbon filament sampler, the next one is the PETG-CF10.... I started printing the coupons as it was wound on the roll, but after a few I decided it probably needed drying.... I dried it at 65C for 6 hours, and indeed it changed the results I was getting.... The strength in the X direction (horizontal) increased from 10,400 psi at 250C to nearly 14,000, which is the highest I have recorded, even stronger than CF-Nylon!.... However, the dried filament LOST strength in the Z (vertical), the layer to layer adhesion dropped from 3300 psi to only 1000 psi !!!!.... The fan setting, at 70% (recommended by Spectrum) seemed high for PETG, so I ran the tests again with the fan at 30% and got a small improvement in both directions.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PETG-CF10_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PETG-CF10_Temp.jpg)
The filament was the strongest in the X direction at 250C, and I had lots left, so I did some tests at 250C, with the 0.25mm layer height I had been using, and also with 0.30mm layers.... The variable this time was the line width, and I only printed the vertical coupons, with the following results....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PETG-CF10_Width.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PETG-CF10_Width.jpg)
In a similar manner to the test I ran with the PLA-CF10, with the thinner layer, the strength improved as I increased the width.... but with the thicker layer, the width of the lines made little difference.... I still had some filament left, so I installed a 0.6mm nozzle (all the above were done with a 0.4mm), and using a 0.6mm line width I printed samples at various layer heights.... Here are those results....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PETG-CF10_Layers.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PETG-CF10_Layers.jpg)
The 0.42mm layer height was not that great a quality, and the 0.48 was pretty awful, to be honest.... The strength in the vertical (Z) direction peaked at a layer height of 0.42mm (70% of the nozzle diameter), and I can't imagine using more than about 0.4mm for anything that you care about the appearance of.... The strength in X (horizontal) peaked at a layer height of 0.30mm, which is 50% of the diameter, just like printing at 0.20mm with a 0.4mm nozzle.... The interesting thing about this test is that it pretty much disproves the "60% rule" for layer height with a Carbon Fibre filled filament.... However, this and the previous test using PLA-CF10 did show that a 0.25mm minimum layer height (60% on a 0.4mm nozzle) was a lot stronger than the "standard" 0.20mm layer height.... My conclusion, based on these two tests, is that you want a layer height of 0.24-0.32mm when using a CF filled filament.... I may refine this as I do further tests with other materials....
Bob
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Next in line in the Spectrum Carbon sampler is their PCTG-CF10, and no that is not a typo, it is not PETG.... This material prints at a higher temperature than PETG, and I had high hopes for an improved layer-to-layer bonding.... only to be disappointed!.... Here is the plot of Yield vs Temperature....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PCTG-CF10_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PCTG-CF10_Temp.jpg)
The Horizontal (X) strength is wonderful (almost 12,000 psi), but the Vertical (Z) strength was well under 2000 psi.... The material had been dried at 65C for 6 hours prior to testing.... I had lots of material left, so I decided to try and answer some nagging questions about whether the cross section layout mattered on vertical prints I had data from the first round with all walls in the test section, so I used the same layer thickness (0.25mm) and line width (0.40mm), and reduced the walls to 4, then 3, then 2, with the interior filled with a 100% line infill, as in the Cura slicer drawing below....
(https://hosting.photobucket.com/images/oo221/rsterne/Various_Walls_in_Z-Coupon.png) (https://hosting.photobucket.com/images/oo221/rsterne/Various_Walls_in_Z-Coupon.png)
I hoped to find out if there was any difference in the way different line orientations bonded, layer-to-layer, or if it was just the cross-sectional area that mattered.... These tests were done at 270C, the upper end of the recommended temperature range for PCTG.... Here are the results: virtually a straight line....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PCTG-CF10_Walls.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PCTG-CF10_Walls.jpg)
To me, this answers the question whether you should favour walls over 100% infill when the load is only trying to separate the layers, and there is NO bending load applied to the part.... it doesn't matter.... NOTE, this is not the case when the part is bending (as in Stefan's test hooks), where the outer layers are under more stress, so of course more walls is better....
I next wanted to find out what difference line width made on Vertical (Z) samples, so I varied the line width (which changes the wall count in the test section) from 7 walls of 0.40mm down to just 4 walls but of 0.7mm.... I did this using a 0.25mm layer height, and then repeated it with a 0.30mm layer height.... I then did some Horizontal (X) coupons at a 0.3mm layer height as well.... Testing again done at 270C.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PCTG-CF10_Width.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PCTG-CF10_Width.jpg)
Once again, we see that with the 0.25mm layer height, there is an increase in strength going from a 0.4mm wall to a 0.5mm, then not much difference going to 0.6mm.... There was another increase in layer-to-layer bonding going to a 0.7mm width (which is 175% of the nozzle diameter), this may be due to the high pressure require inside the nozzle to squeeze the filament out to that extreme width.... When retested with a 0.30mm layer height, the line was much flatter, there being little difference in the strength by increasing the line width.... We have seen this before....
I had some filament left, so I did some Horizontal (X) coupons at the 3mm layer height, again at 270C.... Interestingly, the strength decreased slightly as the line width increased from 0.40 to 0.60mm (100-150% of nozzle diameter).... The 0.25mm layer with a 0.4mm line width tested initially was slightly stronger than the same width with a 0.30mm height.... The difference was not great, and with the Z direction being so much weaker than the X, would not matter on most prints....
My conclusion on this material is that unless you need specific properties where PCTG excells, the Spectrum PETG-CF10 is a better choice (and cheaper)....
Bob
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It seems that the more testing I do, the more questions I have.... I guess that this early on in learning about 3D printing, that is typical.... The first testing I did with PETG-CF filaments, I used them "out of the box", as I thought they should be fine when first opened.... The results are earlier in this thread.... Now I am drying them and retesting.... Just like the Spectrum PETG-CF above, when I retested the IEMAI PETG-CF filament, the strength in X increased but the strength in Z decreased after drying at 65C for 6 hours!.... I don't understand the mechanism by which this is happening, but I need to figure out how to get back the lost strength in the layer-to-layer bonding.... So, I started trying various combinations of layer height and line width, testing at 250C, with the following results....
(https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_Width.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_Width.jpg)
At the "threads" of filament get bigger, I am losing strength in the horizontal (along the threads), but gaining greatly in the vertical (layer-to-layer) strength.... In fact I managed to double that by going from a 0.25mm height with 0.40 mm width to a 0.30mm height with a 0.60mm width.... I then tried printing slower, 40mm/sec. instead of 80, and the horizontal got a bit stronger (10%), but the vertical lost 20% of its strength.... I then tried a speed in between, and turned off the fan.... I lost 10% in the X direction, but made a huge gain in the layer-to-layer bonding, and recorded 5340 psi, which is 75% of the X strength at the same settings.... The failure point showed almost complete fusing of the layers (which is great), but the sides of the square test section were bulged out and no longer straight lines.... Most of the coupon looked OK, but the smallest section, that takes the shortest time to print, was obviously getting too hot and distorting badly....
I think I have zeroed in on a "minimum" height and width for CF filled filament when using a 0.4mm nozzle, however.... There is no question that you don't want to use less than 0.25mm for a layer height, and there is a pretty decent improvement in layer-to-layer bonding by going to a 0.5mm line width (125% of the nozzle diameter).... Further gains in layer-to-layer bonding appear to be available by increasing the layer height, but at the expense of appearance of course.... If you don't mind the layer lines, you can increase the height to 0.3mm and the width to 0.6mm.... At that size, you could (should?) be using a 0.6mm nozzle.... and then you can go even larger, at the expense of pretty terrible looking prints.... For me, the practical maximum would be a 0.36mm layer height, with about a 0.72mm width.... Thicker than that looks pretty ugly, IMO....
Bob
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Sometimes I get carried away with testing, when I could have just watched a video!.... This one on extrusion width by Stefan at CNC Kitchen is really important if you are looking to improve your layer to layer adhesion to increase strength in the Z-direction....
https://www.youtube.com/watch?v=9YaJ0wSKKHA
I am just working through testing my 4th PETG-CF filament chasing this exact thing.... Stefan's conclusion was that you can go to 140-150% of the nozzle diameter without losing print quality, and he used up to 200% for structural prints.... I have already adopted 120-125% as my "standard", and am experimenting with 150%, and I will be posting some graphs shortly.... It really does increase print strength, and an added advantage (as posted by others in this thread) is that increasing the extruded width relative to the height (layer thickness) will allow you to print shallower overhangs without adding support....
Bob
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I have dried some of the PETG-CF filaments that I tested previously right out of the box, figuring they should be OK.... What I found was very interesing.... When dried for 6 hours at 65C, the Horizontal (X) strength increased, but the Vertical (Z) strength decreased (or at best stayed about the same), in all the ones I dried.... Here are the results for the dried filament, you can see the charts for the "as purchased" filaments in the above posts....
(https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Dried.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Dried.jpg)
(https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_Dried.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_Dried.jpg)
(https://hosting.photobucket.com/images/oo221/rsterne/Kimya_PETG-CF_Dried.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Kimya_PETG-CF_Dried.jpg)
In my quest for increasing the layer-to-layer bonding I have been trying an increase in the line width (as in Stefan's video in the previous post).... There is no question that you get an increase in the Vertical (Z) strength as you go to wider lines.... However, the Horizontal (X) strength usually decreases a bit (but not enough to make a significant difference).... Here are my results....
(https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Width.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Width.jpg)
(https://hosting.photobucket.com/images/oo221/rsterne/Kimya_PETG-CF_Width.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Kimya_PETG-CF_Width.jpg)
(https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_Width_6fa5fXtPiHyenVYmvQnk84.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_Width_6fa5fXtPiHyenVYmvQnk84.jpg)
(https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_0.6Nozzle.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/IEMAI_PETG-CF_0.6Nozzle.jpg)
From this experimenting I have decided to use a 0.25mm Layer height, and a 0.60mm line Width (150% of the 0.4mm nozzle) as my standard profile for CF filled PETG.... If you want to print really fast, you could use a 0.6mm nozzle, a layer height of 0.30mm, and a line width of 0.9mm.... maybe even a 0.333 layer height and a 1mm width (although I haven't tried that yet)....
Bob
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i told ya :D
it works even better with pla
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Yeah, you did!.... I just needed to find out how it works with CF-PETG....
Bob
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Bob, did you see this video? Granted the printing is slow but the numbers Stefan got for Z axis were pretty impressive.
https://www.youtube.com/watch?v=9qb25Gi4Jv0
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I wonder how much of the strength was that there were no impurities (ie dye, particles, strands, etc.) in the filament.... I think it's pretty "clear" that pure filaments should be, and are, superior for layer adhesion....
Bob
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I got some Priline PETG-CF a couple of days ago, because I had heard good things about it, and the price was good.... Well, it may be cheap(er), but the performance was the worst carbon filled PETG I have tested, particularly for layer to layer adhesion.... and it was no stronger in X than a non-carbon PETG....
(https://hosting.photobucket.com/images/oo221/rsterne/Priline_PETG-CF_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Priline_PETG-CF_Temp.jpg)
The prints did not show very much of that "carbon look", and I won't be buying more of it.... I'll just use it up when I want a greyish black PETG.... Further carbon filled PETG testing will have to wait until some that I haven't already tested goes on sale.... The strongest in X was the Spectrum PETG-CF10, and it had the most glittery, layer hiding appearance, but the Z strength was below the PETG average.... The second strongest in X was the Kimya PETG-CF significantly better than non-carbon PETG and most PLA, with a Z strength typical for PETG, though not as good as the best PLAs....
Bob
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I tried annealing the Priline PETG-CF.... tested stock vs. 2 temperatures for 4 hours each.... The horizontal strength increased about 6% when annealed at 65C, but was weaker when annealed at 90C.... The vertical strength was less on both annealed samples....
Bob
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I continued my tensile testing of the samples of Spectrum Carbon Fibre filled filaments today with the ASA-X-CF10.... Frankly, I see no advantage over PETG-CF filaments, and it smells quite a bit (somewhat like ABS when you saw it).... The surface finish is quite rough, particularly on the corners, where it ends up with raised ridges like tiny saw teeth, quite sharp.... I am testing all the carbon fibre samples now using a 0.25mm layer height and a 0.50mm extrusion width.... Spectrum recommend 235-260C for the nozzle, and 0-20% for the fan (I had the fan off).... The bed temperature is quite high, I used PEI with Elmer's gluestick, at 90C (100C for the first layer), the recommended is 90-110C, and I had no adhesion problems.... Incidently, the horizontal samples were breaking through the eye, so I had to reduce the test section to just 3 x 4 mm to get clean breaks there (and adjust the area in the calculations, of course).... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_ASA-X-CF10_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_ASA-X-CF10_Temp.jpg)
This material was about 13% stronger than most PETG-CF filaments in X, but more than 14% weaker in Z.... but is was significantly weaker than Spectrum's PETG-CF10 in the horizontal (X) direction (but that was one of the strongest I have tested so far).... When I did a final test with a 0.60mm extrusion width at 270C, it was NOT as strong at the 0.50mm width, quite a different result than I had with the PETG-CF.... With the smell and rough finish, I won't be using it again.... If you want what I have left (~ 150g), just pay the postage and you can have it!.... My wife says I am not to use it any more because of the smell!....
Bob
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I dried my Nylon filaments overnight at 90C, and retested them.... They were stronger (more about that later), but I was still having the occasional coupon breaking through the eye where the pin is.... I can't make that part any bigger, so I redesigned the whole system for new, smaller, faster to print coupons that use half the material....
(https://hosting.photobucket.com/images/oo221/rsterne/Round_Coupons.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Round_Coupons.JPG)
The vertical coupons are round, using a hyperbolic center and conical ends to anchor them.... The horizontal ones are similar, but use the same rectangular test section I did before, at 5mm x 3mm.... I made them that way (with a flat bottom) so that I could print them flat without supports.... Of course this means I had to design and print fixtures to hold the ends of the coupons....
(https://hosting.photobucket.com/images/oo221/rsterne/Fixtures_for_Coupons.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/Fixtures_for_Coupons.JPG)
I printed them from Polymaker PA-612-CF carbon filled Nylon, which has been the strongest material I had tested so far.... They are printed horizontal, with support under the thinner tab, where the pin goes through to mount them on my lathe based testing equipment.... This is what they look like with a coupon in place....
(https://hosting.photobucket.com/images/oo221/rsterne/New_Testing_Setup.JPG) (https://hosting.photobucket.com/images/oo221/rsterne/New_Testing_Setup.JPG)
I have done a lot of testing to insure that the data is consistent with my previous results, and I am delighted with the correlation.... All the coupons break in the middle, in the thinnest section as they should.... The fixtures don't flex, and are showing zero distortion or wear.... They may as well be machined from aluminum, considering the loads they have to stand, which is no problem....
Bob
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Here are the results on the retesting of the two carbon filled Nylon filaments I tested a while ago, after drying at 90C for 12 hours.... First the 3DX Tech PA6-CF-G3....
(https://hosting.photobucket.com/images/oo221/rsterne/3DXTech_PA6-CF-G3_Dried.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3DXTech_PA6-CF-G3_Dried.jpg)
The gain in strength in the X direction (horizontal) is about 1000 psi, but the vertical (Z) direction had a big jump, from 2400 psi to over 8000.... The layer bonding was stronger up to 270C, but at 280C the quality went in the trash, and the Z-yield dropped a lot.... Do not use over 270C for this filament!....
(https://hosting.photobucket.com/images/oo221/rsterne/Polymaker_PA612-CF_Dried.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Polymaker_PA612-CF_Dried.jpg)
For the Polymaker PA612-CF, it also gained a bit in X, and also made a large (30%), gain in Z, ending up at nearly 7000 psi.... After proper drying, both these carbon filled Nylons exceeded even the best of the PLAs that I tested in Z and in X.... Don't think that because they are vacuum packed with dessicant from the factory that you can skip drying them before use, you can't....
Bob
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I tested the last of the Spectrum sample pack today, this time it was the PA6-LW-CF15S.... The "LW" stands for "low warp", and it contains 15% carbon fibre in the Nylon base.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PA6-LW-CF15S_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Spectrum_PA6-LW-CF15S_Temp.jpg)
The horizontal (X) strength was nearly 12,000 psi, which is right in there with the other Nylon filaments in the previous post.... The vertical (Z) direction was the strongest I have tested, at over 9,500 psi, which is 80% of the filaments printed in line (X).... That is quite astounding layer-to-layer adhesion.... Not only that, but from 250-290C the performance in both directions was pretty consistent.... At 300C, however, the strength in both directions dropped off rapidly.... The narrow part of the vertical coupon was shiny and irregular.... At 290C there was lot of stringing, and a bit at 280C, but at 270C the print quality was quite good.... This filament definitely is on my short list.... It doesn't print quite as nicely as the Polymaker PA612-CF, but a lot easier to print than the 3DXTech PA6-CF-Gen3.... I am finally seeing just how good a good quality carbon filled Nylon can be.... 8)
Bob
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Bob,
How's the print quality at 250C? I dare not go higher on my stock hot end, but these numbers truly impress. Are you using an enclosure? and has it lived up to the "LW"? Where did the sample pack come from? A quick google doesn't show many vendors for this brand in the Americas. Thanks!
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Those are nice numbers. Apparently Nylon looses strength as the moisture is reabsorbed. It may be interesting to set aside several coupons and let them reabsorb moisture for several weeks
Example: https://www.degruyter.com/document/doi/10.1515/SECM.1995.4.3.199/pdf
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Print quality is good at 250-270C.... I haven't seen any warping with the Nylon, but I have been using a Garolite bed at 100C.... No enclosure on my Ender 5-S1, but it is tucked into a corner in a draft free, unoccupied room I keep at 21C (70F) when printing.... I got the sample pack from 3D Printing Canada....
https://3dprintingcanada.com/products/carbon-set-multi-pack-1-75mm-spectrum-carbon-filament-5-x-0-25-kg
I am still collecting various types of PETG-CF, you can print it at lower temperatures than Nylon and it's less hygroscopic.... The Spectrum version was as strong as the Nylons in X....
Bob
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Thanks for the link -- ~$60 a half kg -- pricey but worth it if the application calls for it.
PETG-CF that's as strong in the X as this nylon is well and good -- but I'm interested in a strong Z -- the weak link. This latest filament is gangbusters in that regard. Since the CF mostly works in the XY direction, the non-CF version of this PA6 may also be excellent in the Z, but with a hit to the XY performance. Won't look as cool, though, the more matte CF appearance is very appealing.
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The fusing of Nylon between layers is impressive.... Most of the good test coupons look rather "crystalline" in appearance with few or no layer lines visible.... That is obviously the secret to their above average "Z" performance....
Bob
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I needed some green PLA for a project, and purchased some of the "house brand" from 3D Printing Canada.... It printed beautifully, and when I was finished my project I tested the leftover filament.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_PLA_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_PLA_Temp.jpg)
It was right in the ballpark for strength in both directions, a little stronger in X and a little weaker in Z (layer bonding) than the "brand name" PLAs I tested previously, and wayyyyyyyyyy better in both directions than the "Econo PLA" from Overture.... so good value for money.... The highest strength in X was at 220C, and in Z it was at 210C, but so close in layer bonding that I decided to do some additional testing at 220C to find out what happens with different Extrusion Widths, both staying with a 0.2mm layer height (and varying the widths), and increasing the layer height as the width increases, maintaining a 2:1 ratio of width to height.... In other words, 0.20mm layers with 0.40mm width, 0.25mm layers with 0.50mm widths and 0.30mm layers with 0.60mm widths (all done with a 0.4mm nozzle).... Both sets of results are plotted below....
(https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_PLA_Width_Height.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_PLA_Width_Height.jpg)
As I have seen before, there isn't any advantage in the horizontal (X) direction from increasing the extrusion width (or the layer height), but increasing the width of the strands increases the vertical (Z) strength significantly.... The gain was pretty linear with a 0.20mm layer height, but when you increase layer height in proportion to line width, the gain was greatest with a 0.25mm layer height and 0.50mm line width.... I have seen this before with other filaments....
Bob
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Well, I made a big mistake on this post, which I am now correcting.... I had the wrong number in my spreadsheet for the width of the horizontal (X) coupon, so the yield values I reported for the horizontal (X) yield were lower than they should have been.... The vertical (Z) yields were correct, however.... I have corrected the charts, and I am editing the text to correct this error.... For anyone who read the original version, or to the Manufacturers of the two filaments involved, my apologies....
I recently purchased four more brands of PETG-CF filament (well, once was PET-CF), to continue my testing to find a good one.... Neither of today's candidates qualify.... First I tried the BAMBU Labs PETG-CF, and in both the horizontal (X) and vertical (Z) directions it was weaker than the non-CF filled PETGs I haver tested.... Here are the results....
(https://hosting.photobucket.com/images/oo221/rsterne/Bambu_PETG-CF_Temp_hsoyD1wqe7XCFzjyMZhtAZ.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Bambu_PETG-CF_Temp_hsoyD1wqe7XCFzjyMZhtAZ.jpg)
So I figured after that disaster, I would get a reprieve when I tested one of the highly touted 3DXTech filaments, their PETG-CF.... Here are the results for that....
(https://hosting.photobucket.com/images/oo221/rsterne/3DXTech_PETG-CF_Temp_wfxmt1qwytN7vBxZ3XTW2P.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3DXTech_PETG-CF_Temp_wfxmt1qwytN7vBxZ3XTW2P.jpg)
It was about average for the carbon filled PETGs in X.... but easily the weakest of all the filaments of any kind I have tested in Z, with the exception of the Econo PLA I tested.... 3DXTech recommend using 230-260C for this filament, and it was under 1000 psi for layer-to-layer adhesion, which means the coupons were breaking at less than 30 lbs. of pull.... Even at 280-290C it didn't reach 2000 psi.... :o
I am getting quite a collection of PETG-CF filaments that look pretty but are weaker than regular PETG.... Oh well, still a couple more to go tomorrow.... ::)
Bob
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While I was preparing today's data, I discovered an error on the charts (and text) for the previous post, which I have now corrected, please check out the changes above....
Today's data is for the remaining carbon filled PETG I have, made my 3D Printing Canada, and for the Bambu PET-CF (note, not PETG, and over double the price per kg.).... First for the 3D Printing CF-PETG....
(https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_PETG-CF_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_PETG-CF_Temp.jpg)
It was pretty typical in the horizontal (X) direction for the CF filled PETGs I have tested, but a bit below the average in the layer-to-layer adhesion.... None of these CF-filled PETGs have been stronger than non-CF filled PETG in the vertical (Z) direction so far.... Next I tested the BAMBU Labs carbon filled PET filament.... This is not PETG, and has a noticable odour when printing.... It costs about twice what their CF-PETG does by weight.... Here are my results....
(https://hosting.photobucket.com/images/oo221/rsterne/Bambu_PET-CF_Temp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Bambu_PET-CF_Temp.jpg)
The printing temperature was higher, with the strength peaking at 280-290C.... It was significantly stronger than their PETG in the horizontal (X) direction, reaching nearly 12,000 psi.... However, it was disappointing on layer-to-layer adhesion.... performing much like a typical PETG in that regard.... For my next tests I am putting on a 0.6mm nozzle, and do some experimenting to see if I can increase the strength in the vertical (Z) direction on a few filaments....
Bob
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I have just noticed that I used the incorrect cross section for some of the vertical coupons below where testing was done with a 0.6mm nozzle.... The corrected layer-to-layer strength (Z) is less than I originally published :-[.... I have replaced the last 4 charts and corrected the comments for the following filaments:
3DXTech CF-PETG
Polymaker PA612-CF
Anycubic PLA
3D Printing Canada PLA
The biggest change is that the Z strength does NOT approach the X strength, I should have known there was a mistake when I saw that....
I have mostly worked my way through the materials I have on hand, so I installed a 0.6mm nozzle to do more testing.... I have found that using greater extrusion widths increased the layer-to-layer bonding, as per the CNC Kitchen video testing that Stefan did.... He found the maximum strength occurred at about 150% of nozzle diameter is his tests, and I have confirmed that.... So, that has become a goal for parts that require maximum strength.... I tested quite a few materials, looking at extrusion width in some, layer height in others, and in some, both.... Here are all the charts, with a few comments after each one....
(https://hosting.photobucket.com/images/oo221/rsterne/Bambu_PET-CF_Width.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Bambu_PET-CF_Width.jpg)
This one shows an increase in strength with a 0.4mm nozzle going from a 0.50mm width to 0.60mm (150%), and the same results with a 0.6mm nozzle peaking at a 150% width (0.90mm) and then starting to decline....
(https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_CF-PETG_Width_ahKmB1KWcN9pXgChtX7oCw.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_CF-PETG_Width_ahKmB1KWcN9pXgChtX7oCw.jpg)
This one shows the peak at 1mm width (166%) in both directions, and a very sharp decline in strength in the horizontal (X) direction above that....
(https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_CF-PETG_Layer.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_CF-PETG_Layer.jpg)
This one, using the same filament and a 1mm width (the peak above) showed a decrease in the vertical (Z) direction as the layer height increased, with a slight increase in horizontal strength from a layer height of 0.25mm to 0.30mm, and then a steeper decline above that....
(https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Width_brXMGJ6bVupDAWWGwri2BM.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Width_brXMGJ6bVupDAWWGwri2BM.jpg)
This one showed an increase in Z with the 0.4mm nozzle at 150%, but a decrease in X.... However with the 0.6mm nozzle, both peaked at 150% (0.90mm)....
(https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Layers.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG-CF_Layers.jpg)
With the same material, using a 0.6mm nozzle and two different extrusion widths, 0.9mm and 1.0mm, the horizontal (X) strength peaked with a 0.30mm layer height, and the vertical strength with the 0.90mm width also showed a slight peak at 0.30mm layers, but using a 1mm width the layer-to-layer bonding decreased as the layer height increased.... The next three tests focused on varying the layer height while using 150-166% of nozzle diameter extrusion width (at this point, a "proven" maximum)....
(https://hosting.photobucket.com/images/oo221/rsterne/Kimya_PETG-CF_Layers.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Kimya_PETG-CF_Layers.jpg)
This clearly shows a decrease in strength with increasing layer height.... Note that for all three of these charts, the extrusion width was 0.90mm (150%) for the 0.25 and 0.30mm layer heights, but I used 1mm for the 0.33 height (3:1 bead)....
(https://hosting.photobucket.com/images/oo221/rsterne/3DXTech_PETG-CF_Layers_2f2XsuNPkqd7qUYyzUjbED.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3DXTech_PETG-CF_Layers_2f2XsuNPkqd7qUYyzUjbED.jpg)
This shows a fairly dramatic decrease in X with increased layer height, the layer-to-layer strength was relatively constant....
(https://hosting.photobucket.com/images/oo221/rsterne/Polymaker_PA612-CF_Layers_22qiWanrzxkzHLzwAMUgLp.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Polymaker_PA612-CF_Layers_22qiWanrzxkzHLzwAMUgLp.jpg)
The Nylon acted a bit differently, the strength in both directions increased with greater layer height.... The broken "Z" coupons showed no layer lines with the thicker samples, and a somewhat "crystalline" appearance.... Next I tested two PLAs....
(https://hosting.photobucket.com/images/oo221/rsterne/Anycubic_PLA_Layers_nMX5ZrZraYXjaeXA2SeL7J.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Anycubic_PLA_Layers_nMX5ZrZraYXjaeXA2SeL7J.jpg)
At a 0.20mm layer height, the strength was a lot lower.... Greater strength in Z but less in X with the 0.6mm nozzle....
(https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_PLA_Layers_dDCDiF25zupYLgy8Jk7rQQ.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/3D_Printing_Canada_PLA_Layers_dDCDiF25zupYLgy8Jk7rQQ.jpg)
A different PLA, showing a similar graph....In both PLA tests, however, the horizontal (X) strengths were lower than what I got for the same filament when testing with a 0.4mm nozzle and 0.20mm layer height (the typical printing profile for PLA)....
Now for my conclusions.... First of all, print quality depends mostly on layer height, and is basically unaffected by the extrusion width, up to 150-160%, as Stefan also found.... Requirements on the appearance of layer lines will vary with personal preference and the job at hand, but the "standard quality" using 0.20mm for PLA is good enough for me, although for shallower angles (eg. on the top of a sphere), thinner lines definitely help, so the "adaptive layers" function in Cura is helpful for that.... However, I am convinced that for carbon fibre filled filament, you should not use a layer height less than 0.25mm, which because of the matt finish doesn't show the layer lines too much anyways....
In terms of the extrusion width, I have not seen any significant deterioration in print quality by using widths of 150-166% of the nozzle diameter, and it certainly speeds up the printing process and increases the strength in the vertical (Z) direction, by up to 50% or more.... This seems to be a no-brainer, both stronger and faster.... This means an extrusion width of 0.60mm for a 0.4mm nozzle, and 0.90mm for a 0.6mm nozzle.... With some filaments there is, however, a small loss in the horizontal (X) strength, and it may really drop off above 166%....
The effect of layer height on strength is something that Stefan looked at, and his conclusions were that you wanted to stay below 50% of the nozzle diameter, that the strength decreased above that.... About half of my tests with the 0.6mm nozzle confirmed that (ie maximum height of 0.30mm), the rest didn't.... When using CF filaments, you just shouldn't use anything less than 0.25mm, IMO.... In many instances, going to a 0.6mm nozzle lost a bit of horizonal (X) strength compared to a 0.4mm nozzle, but that may be a result of the small cross section of my coupons, which are only 3x5mm.... I have a gut feeling that in the horizontal (X) direction, lots of small lines, rather than a few larger ones, give greater strength, up to a point.... This may be the reason for the decrease in strength using a larger nozzle.... In the "Z" direction, however, where layer-to-layer bonding is critical, the higher pressure caused by a 150% (of nozzle diameter) extrusion width is also increased by a small layer height, but once you go above a certain height, that pressure drops and you lose strength....
So, remarkable increases in layer bonding strength can result from using 150% extrusion width, and if you go to a 0.6mm nozzle of course the printing time drops by about a third.... If you combine the two, you can print in less than half the time than with a 0.4mm nozzle.... Here are some suggestions you might like to try....
Non CF filled filament
0.4mm nozzle....0.20mm layer height with 0.60mm extrusion width....
0.6mm nozzle.... 0.25-0.30mm layer height with 0.90mm extrusion width....
Carbon fibre filled filament
0.4mm nozzle.... 0.25mm layer height with 0.60mm extrusion width....
0.6mm nozzle.... 0.25-0.30mm layer height with 0.90mm extrusion width.... for faster printing, 0.33mm layer height with 1mm extrusion width....
Bob
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Bob,
I appreciate all the testing you've done -- great data to show general trends, and specific data on so many brands. Thank you!
I have been mulling the data, and I've seen a "disconnect" a few times -- always with CF filaments. If you use say, a 0.6 nozzle, with 0.60 line width and 0.30 layer height, and compare that to the 0.4 nozzle with 0.60 line width and 0.30 layer height, there is a VERY significant increase in Z strength (layer bonding) for the smaller nozzle, even though the "bead size" laid down is identical. Did speed of print mm/s change? Did flow rate mm3/s change? That could be significant. Speed and flow aside, it may be that forcing the molten CF infused filament through the smaller nozzle causes a more turbulent flow, and the CF fibers are "jumbled up" rather than "laid straight" -- causing a rougher surface and more vertical fibers to aid in a stronger bond to the next layer?
I looked and did not see a lot of evidence to prove that non-CF filaments have the same remarkable increase in strength when the line width is 150% of nozzle width, versus using a larger nozzle at 100% line width. Can you test a few regular PETGs and see if they also benefit? Cura's layer view preview will also show the speed and flowrate -- obviously those numbers would be most useful in the area of the specimen intended to be broken. Ideally the speed and commanded flow should be the same for both nozzle sizes.
Here's the CF graphs that exhibit what I'm talking about. On one, I added a data point from one of your other graphs, rather than add it here too.
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When you print with a larger nozzle and lay down the same width line (at the same layer height), the pressure in the larger nozzle is less.... I think basically the higher the pressure in the nozzle, the greater the Z strength (eg. your first chart)....
The PLA I tested with the 0.6mm nozzle, the X strength was less than with the 0.4mm nozzle, but the testing I did with the 0.6mm nozzle had a 0.9mm (150%) width for the 0.20-0.30mm layers, and a 1mm (166%) width for the 0.33mm layers.... The earlier testing I did with PLA was a 0.2mm layer and 0.4mm (100%) width, and the Z strength went from about 50% to 100% (with X reduced), or from about 5K to 8K, a big increase with the wider lines....
Where do you find the flow rate in Cura, I have missed that?....
Bob
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Bob,
I found your two PLA graphs, one 0.4 nozzle, the other 0.6. As you can see, when comparing the Z strength of a 0.60 line by 0.30 layer height, the 0.6 nozzle is the (slightly) stronger layer bond. In this case, the higher pressure is not making it significantly stronger. The CF filaments however, do seem to be benefiting from the smaller nozzle.
Cura Flow is in the Layer Preview screen Color Scheme pulldown.
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Thanks for that, Bob, much appreciated.... Yes, the flow rate in the test section of the vertical (Z) coupons is very slow.... Perhaps that is why on some coupons I was getting failures further out towards the ends instead of in the middle, where they should break.... The variations in strength on those charts are so small, they may well be within statistical (testing) error.... I would not put any faith in comparisons of data within 5% or less (maybe even 10%).... For example, on that 3D Printing Canada PLA, the wavy line for the vertical strength could just as likely be a straight line, slightly higher on the right, instead of up-down-up-down....
Bob
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On the flow, no prob, Bob!
Also be sure to look at the same Color Scheme pulldown for Line Width. If you are using Cura 5.x, it may use varying linewidths around your base chosen linewidth, sometimes up to almost 2x. If you are setting your base line width to 1.5 nozzle width, Cura may be increasing it to 3x nozzle width!
On the PLA curves, I think you are missing my point. Yes, the PLA 0.6 nozzle using 0.60 line width and with 0.30 layer height has almost identical Z strength to the 0.4 nozzle using 0.60 line width and 0.30 layer height. There is no Z-strength advantage to using the smaller nozzle.
On the PETG-CF, on the other hand, there is a sharp increase in Z-strength in the same nozzle/line width /layer height test comparison. The smaller nozzle is showing a huge increase in Z-strength compared to the larger nozzle.
The question is -- is that because it's CF, or because its PETG? So that was why I asked if you could run the same tests with some regular, non-CF, PETG. Hope this makes sense.
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Got it!.... I will try some PETG with different Extrusion Widths, etc. when I get some time.... Right now I am tired of testing and have a project I'm working on!....
Bob
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Sounds good Bob, thanks.
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I had a look at the other Dropdowns in Cura, it is very interesting to see what actually happens!.... I found no change in layer height (unless using Adaptive), nor anything really in line width, except the center "dot" in the test coupons.... However, the test sections of the coupons are printed MUCH SLOWER and with MUCH LESS FLOW because they are so small in area!.... Of course I can't print them large enough to avoid that, or they would be wayyyyyyyyyy too strong for my machine to break them!.... What difference that makes in the actual strength on a part printed "normally" (ie as intended) I have no idea, and it may be a bit of a stretch to think that all filaments would give proportional results at my test conditions as when printed at intended speeds and flow rates.... ::)
Bob
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Hi Bob,
I had been wondering if you had a chance to look at all the useful info in the pulldowns.
For linewidth, explore a hollow model with a gradually increasing thickness outer shell for instance -- even a solid cone may work with 100% fill and concentric fill pattern on top/bottom -- the linewidth will probably vary through most of the range the default parameters are set for. For a 0.50 default linewidth, most of it is printed at 0.50, but part will have lines as narrow as 0.425 (sometimes even lower) and as high as 0.85 - 0.89 -- to fill the gaps better. The print speed typically varies inversely with the linewidth such that the flow remains constant.
I just checked something on solid prints -- the variable linewidth mostly affects concentric fills. If you use lines or zig-zag fills, it may not show up at all. I find that concentric often leaves fewer unfilled gaps than the linear fill patterns.
I believe what you are seeing with the less speed and less flow in your vertical specimen necks -- is you running up against the "minimum layer time" and/or the "minimum print speed" in the Cooling section. Are you looking with just one on the plate, or several? If you printed multiple specimens "all at once" I believe the necks should print the same speed and flow as the rest of the specimen. If not, you may need to add more specimens (or timewaster columns) or set min layer time a bit lower.
There are also special settings for printing "small features" -- which I have not messed with and I believe are disabled by default -- could also affect your print speed and flow in the necks.
That's the $1000 question -- how the slower printing (if it really was slower) affected neck strength -- and does it affect all filaments the same? I would venture to say the existing test results are still quite close, but the error bars around them may expand a bit. Maybe pick ONE of each type of filament (PLA, PETG-CF, Nylon, etc), tweak the setup so a specimen prints at the intended speed (with ample time between layers), and compare the new results to the originals. If the results are still about the same, great, note which direction strength changed and call it done. If they change dramatically... well ... just hope that they don't. :)
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I was only printing one specimen at a time (well 1 X and 1 Z, but the Z is only 3mm tall, so if doesn't affect the test section of the Z coupon), as sets are done at different temperatures (for the most part).... My testing method seems VERY consistent, and even with only 1 sample per variable, the curves are pretty fair.... Yes, the minimum layer time is the likely culprit, I think.... The "official" tensile test specimens (can't remember the number) doesn't have a huge test section.... It isn't an issue printing in X, only in Z....
Bob
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TorqueMaster.... I found an error in the last 4 charts I published, I used the wrong cross section for the Z coupon.... The correct strengths are significantly lower than what I previously published.... In particular, the PLA layer-to-layer (Z) strength was nowhere near the X strength, sorry for that mistake.... :-[
I did the tests you requested on plain Eryone PETG, here are the results with both nozzle diameters.... I used extrusion widths from 100-150%....
(https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG_Width.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG_Width.jpg)
(https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG_0.6N_Width.jpg) (https://hosting.photobucket.com/images/oo221/rsterne/Eryone_PETG_0.6N_Width.jpg)
I hope you can make some sense of these results.... I think the reduction in horizontal strength with the 0.6mm nozzle is due to the much smaller number of strands in the test section.... We seem to be getting than in a lot of samples.... ::) .... In some cases, the X test section printed with the 0.6mm nozzle is delaminating before it fails....
Bob
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Bob,
Thanks for the corrections. I'm still trying to re-wrap my head around all this. I think I see it like this:
The PLA graphs now show the significant increase in Z strength when a 0.4 nozzle is used at 0.60 linewidth vs a 0.6 nozzle used at 0.60 linewidth. (both at 0.20 layer) This agrees with the PETG-CF results.
Thanks for doing the PETG (non-CF) tests! They also agree -- the 0.4 nozzle doing the 0.60 line is Z stronger than the 0.6 nozzle doing a 0.60 line (both at 0.20 layer) About 5250 vs 4200.
It does appear it's "always" stronger in the Z when the nozzle is printing lines wider than the nozzle size, and best in that 125-150% zone, and shooting for 3:1 linewidth:layer height looks smart, too. The caveat would be the graphs where you found layers under 0.20 or 0.25 had lost some Z strength -- a minimum layer thickness is generally required as well.
These are some *REALLY* useful fundamental guidelines for strong parts. If one prints around 3:1 as above at a thickness of 0.2 of 0.25, one may need to slow down print speed to not exceed max flow of the printhead. Creality has probably improved this from the Ender 3, but I have discovered my printer's limits -- when printing wide and "thick" for best Z (and overall) strength, I am printing at a relatively slow printhead speed now. Layer height ignored...print quality improves (less artifacting), and it's still creating prints as fast as it is capable -- win win.
I'm attaching a graph of what happens when you ask a hotend for too much flow. Ender 3's are supposedly capable of ~10mm3/s. What they don't often mention is that is for PLA. When printing in PETG, the max flow is reduced -- best I can tell, it's about the higher temperature needed to melt it (and more heat lost to the room) as well as higher viscosity. My printer has a lot of hours on it, I do not know if this is typical or not. The blue line was some typical test prints, the green some test cubes, all weighed vs what their expected weight should be. They overlap pretty well.
So a possibility on the de-lamination of your X specimens, could be underextrusion if the print speed and resulting flow on them is getting off the ideal line.
Fun stuff, these printers!
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I haven't explored the maximum flow on my Ender 5-S1, that is something I need to do.... When printing with CF filled material, virtually all the manufacturers say to use a slower speed.... I am now using a default of 80mm/s, which of course only does that on the infill.... The walls, top & bottom are printed at 40mm/s, so it's fortunate that using a 0.6mm nozzle with a 0.3mm layer height and a 0.9mm extrusion width gives me the best strength, along with a quality I can live with.... The CF texture hides the layer lines "good enough" for airgun parts, IMO....
Would I be correct in assuming that to calculate the flow you take a rectangle of (height x width) time the linear speed?.... For example, for my 0.3mm layers with a 0.9mm width at 40mm/s that gives (0.3 x 0.9 x 40) = 10.8 mm^3/sec.... I wonder if that is within the capabilities of the Spider hot end on the 5-S1 ?.... I know my print times are slightly less than that predicted by Cura....
Bob
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....
Would I be correct in assuming that to calculate the flow you take a rectangle of (height x width) time the linear speed?.... For example, for my 0.3mm layers with a 0.9mm width at 40mm/s that gives (0.3 x 0.9 x 40) = 10.8 mm^3/sec.... I wonder if that is within the capabilities of the Spider hot end on the 5-S1 ?.... I know my print times are slightly less than that predicted by Cura....
Bob
I would use the preview pulldown to see the flow or flow range in a given print. But yes, the method you state should be very close. I believe Cura models its volume estimates on a slightly bulged/rounded rectangle cross section.
Sometimes my Cura print time estimates are right on, other times they are a little bit high, as much as ~10%. It seems like all the info they need should be there, not sure why it isn't spot on. All my best guesses -- hardware limits, ignoring acceleration times -- would have the print taking LONGER than estimated, not shorter.
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https://www.cnckitchen.com/blog/extrusion-system-benchmark-tool-for-fast-prints
i have used this to test the stock hotend on the sovol
i can attest that when using 0.2 LH / 0.8 LW / 0.6 nozzle the hot end clogs sometimes from too much back pressure
but you can always increase nozzle temp and throw another variable in the mix xD