Three Maxim inspired short, fat LDCs: .177 / .22 / .25

[subscriber]

Might be interesting to add a segment that is only a spacer, with full volume and no baffle. Then one could compare the benefit of baffles vs. volume.

Excellent idea, Stan

See images below. 

STL can be downloaded from wetransfer for 7 days:  https://we.tl/t-Oawnqo3H80

[subscriber]

sliced them in cura 5.2.1 the 3 on the table would take 9hr 35min  60g an 19.51m of material. on the vyper.

 I suspect that I am to blame for longer than expected print times.  The fine knurling with nice looking corner radii create a lot of steps to print.  A coarse gripping feature left sharp would print faster...

[subscriber]

I am going to try the modular.  First item up is the muzzle end.  This time with the internal threads up.  I will slice at 0.15mm, no supports, 100% infill, no brim.  Hope that is ok.  I'm using PLA for this.

Should not have any trouble, assuming your printer is set up so it could print a solid cube without trouble.

Note the images below.  The dotted line is the platen printer.  The "Vs"  indicate potential risk for bridged features.   These may require supports to print.  The finer the resolution setting, the more likely they will print OK.  If those curves end up slightly flatter on top that will still work OK.

The floating features are not OK.  They will collapse in a mess (and most everything above them), unless supports are turned on.  Slice and print the part turned the other way round.

[WhatUPSbox?]

Some info on PEI

[subscriber]

Bruce,

If you are looking for related parts that are easier to print, start with these:  https://www.gatewaytoairguns.org/GTA/index.php?topic=203825.msg156385715#msg156385715

You still need to print them with the small end of the cones pointing up away from the platen.

wetransfer link expires in 3 days for those part...

[subscriber]

Might be interesting to add a segment that is only a spacer, with full volume and no baffle. Then one could compare the benefit of baffles vs. volume.

Excellent idea, Stan

And I forgot to add, the spacer would not only add expansion volume; it would add stand-off distance to the next air stripper.    This is useful for filtering out reflected sound waves, after the bulk pressure has already dropped.  (An analogy to this is your field of view when looking through a peep sight aperture.  The further your eye from the hole, the more area the rim of the aperture blocks from your field of view) 

Whereas, to your point; adding one or two spacers early on in the stack, would be useful to drop the bulk pressure significantly.  Then, managing a larger volume of air at a lower pressure through subsequent stages. 

I would suggest adding a spacer (or two) as the second section in the screw-on stack, if you are shooting a high power PCP; especially if it does not have a working shroud volume to act as a first stage to reduce bulk pressure.  Else, the layer to layer adhesion strength of 3D printed parts would more severely tested.  For lower power shrouded PCPs I think a spacer as the last stage would do more good - easy enough to try.

[WobblyHand]

Well I printed the muzzle end, the right way up, last night, and it seemed to come out ok.  The 100% infill part is nearly twice as heavy as the 15% infill part.  There is a line present in places, probably where the track started and ended.  Might be due to the simple slicer setup.  It is not too bad, though, I'd try it at least on a lower power device.  I will try another section now.

[WobblyHand]

Printed the extender tube.  @subscriber, I think you should add a feature on the rear cap to hold on to, or get a wrench on.  There's nothing substantial to hold onto when threading together.  If there was a hex or some flats it would be better.  Even another knurl would be ok on the rear cap.  More accurately, I can't apply the necessary torque because the there's practically nothing to grasp on the rear cap, and it gets worse as it is screwed in. 

After a bit of puttering about, I found a pin spanner, and lubed the threads with lithium grease and was able to thread it all the way in.  Effort was greatly reduced with the grease, but still needed the spanner.  I used a pin spanner that is used to tighten 4-1/2" grinding wheels.  Still think having a feature to get a wrench on would facility assembly.

This unit is pretty big!  I knew that going in, but, yeah, it's pretty big.

[subscriber]

Bruce, those prints look really nice. 

The vertical line you mentioned is where the extruder started and stopped a layer; and has no of air flow effect.  If it bothers you, I believe there is a way of staggering those start/stops in Cura.  They show as white squares when you preview a sliced part in Cura.   

Some would argue that staggering the start/stops will make for a straighter part; or a stronger part.  They may be right.  I think it may also slow printing down.

Thanks for the feedback about gripping the rear cap.  If I extended the ribs that are on the rear of the cap over onto the OD of the part, would that do?  So, robust knurling of sorts.   Perhaps I should do it so you can see.  Or as you asked, just add a hex for a wrench.  Being able to put it together by hand is the goal.

[WobblyHand]

Bruce, those prints look really nice. 

The vertical line you mentioned is where the extruder started and stopped a layer; and has no of air flow effect.  If it bothers you, I believe there is a way of staggering those start/stops in Cura.  They show as white squares when you preview a sliced part in Cura.   

Some would argue that staggering the start/stops will make for a straighter part; or a stronger part.  They may be right.  I think it may also slow printing down.

Thanks for the feedback about gripping the rear cap.  If I extended the ribs that are on the rear of the cap over onto the OD of the part, would that do?  So, robust knurling of sorts.   Perhaps I should do it so you can see.  Or as you asked, just add a hex for a wrench.  Being able to put it together by hand is the goal.

Pretty happy with them once I figured out the spanner and lithium grease.  That made things a lot easier.

My first thought was a hex or a set of flats.  Assembling with the spanner wasn't bad, but not everyone has a pin spanner.  In the end, a wrench might be better.  My thinking is, this has to tighten onto either a barrel or an adapter.  And it has to come off at some time.  I'd rather have a wrench than use a pin spanner.  If you made the ribs extend to nearly the same diameter of the knurl, it might be ok as well.  It would be best not to need any tools, but if a tool is required, it should be a common tool and unlikely to slip or mar the barrel adapter or the barrel.

Printing a baffle now.  Good thing I have Octoprint running, so I can remote into the printer.  Otherwise I'd be staring at it all the time. 

[subscriber]

Bruce,

I modified the rear endcap for the stackable Maxim baffles to have aggressive grippy features to facilitate screwing baffles together.  The OD matches the OD of the other parts' gripping features.   The fewer larger features reduces file size and should print a bit faster. 

The STL files for all three calibers can be downloaded from wetransfer for 7 days in one zip file from this link:    https://we.tl/t-9YiMt7g24X

The differences between parts by caliber are subtle, so you might not be able to detect it from the images (the left most endcap is .177, then .22 then .25).  The "nozzle" cone diameter is wider as the caliber gets larger, because the mating air stripper cone and bore diameter are larger for each larger caliber.

[Baco]

that was a good move, always suffered trying to screw PLA pieces together...
one thing that seems to help here is using a layer height multiple of the thread's "teeth" height say 0.15 LH for 0.30 thread
also varying print speed and air flow to avoid sagging

[subscriber]

If the more robust gripping features screw on rear endcap design is good for the toroidal spiral, then it is good for the simple conical baffle set.   

So, I created a grippy rear endcap version to go with these baffle stacks that have a simple conical air stripper - this post:  https://www.gatewaytoairguns.org/GTA/index.php?topic=203825.msg156385715#msg156385715

A single rear endcap part serves all calibers for the simple conical baffle stack - see images below.

The zipped STL file can be downloaded from this link for 7 days: https://we.tl/t-10PyFXBiXf

[WobblyHand]

Bruce,

I modified the rear endcap for the stackable Maxim baffles to have aggressive grippy features to facilitate screwing baffles together.  The OD matches the OD of the other parts' gripping features.   The fewer larger features reduces file size and should print a bit faster. 

The STL files for all three calibers can be downloaded from wetransfer for 7 days in one zip file from this link:    https://we.tl/t-9YiMt7g24X

The differences between parts by caliber are subtle, so you might not be able to detect it from the images (the left most endcap is .177, then .22 then .25).  The "nozzle" cone diameter is wider as the caliber gets larger, because the mating air stripper cone and bore diameter are larger for each larger caliber.

Thanks for making those changes. 

Had my first disaster, i.e. spaghetti incident.  Was printing a second baffle and after 3mm of height, the piece disconnected from the platter.  Might be that the Z height is wrong in that corner.  I was moving the print around on the platter, to even the wear on the PEI coating.  Apparently the bottom right side isn't quite leveled out, or it wasn't clean enough.  Either way, I killed the print.  I will move the print to a location that is closer to where I have gotten decent prints.  Guess I need to print out the single layer squares to make further adjustments.  Lots to this.

[WhatUPSbox?]

Printed threads have a rougher texture than cut threads. Usually just working them against each other a few times will loosen them. The threads that start on the bed can have extra squeeze-out (elephant's foot) that makes the initial diameter smaller. Running a deburring tool or sanding will open that up. Sometimes, I'll lightly sand the male threads to knock off any minor imperfections. For smaller threads (1/2-20, etc) I'll run a bolt or even a tap through a few times. I've also used teflon tape instead of lube sometimes.

[TorqueMaster]

Note the images below.  The dotted line is the platen printer.  The "Vs"  indicate potential risk for bridged features.   These may require supports to print.  The finer the resolution setting, the more likely they will print OK.  If those curves end up slightly flatter on top that will still work OK.

The floating features are not OK.  They will collapse in a mess (and most everything above them), unless supports are turned on.  Slice and print the part turned the other way round.

I just found this thread and would like to offer a couple thoughts:

The areas you indicated should print fine without supports -- but depending on how well tuned the printer is -- temperature, cooling, correct extrusion rate --  there may be significant sagging there.   Will sagging there significantly affect the effectiveness of the LDC?  Is the smooth gentle curve fundamentally required?

For threads, I prefer 2mm pitch if possible -- reason being that I can knock out a print way faster at 0.28mm layer height with 2mm threads than needing to slice and print at 0.16 or 0.12mm to get clean threads with 1mm pitch. 

Which leads to the next question -- a repeat from above -- how critical is smoothness inside these LDCs?  Printing at 0.28mm layer height is obviously going to cause more "stairstep" to the curves than printing at 0.12mm....perhaps these NEED to be printed at finer layer heights, and just plan on that, and the extra time involved?

Grippy knurling is great -- and what you do looks awesome -- but yes, can significantly add to print time.  I'm trying to think of a good compromise...it really doesn't have to be raised much, so less depth is less printer zig-zagging.  A simple smooth hex is quick and ideal to get a grip with a wrench if it comes to that...

Which leads to a comment for those new to 3D printing.  Do some reading on properly tuning your printers, and go through those steps.  Make sure 100mm of commanded extrusion gets you 100mm of filament used.  Print some test parts with walls 2 or 3 lines thick, and measure the result with calipers -- ideally to the 0.01mm -- to dial in the extrusion % you need to use.  Ideally, you would do this for every filament you buy, but at LEAST do it for each type (PLA, PETG, etc.)  Print temperature towers to dial in the best print temperature for each filament as well -- for appearance, sagging, and stringing. 

As suggested, print these LDC parts at 100% infill for strength -- they are small, and filament is cheap, no need for saving a few grams.  BUT -- when printing at 100% infill, it is even more critical to get your extrusion % correct.  For PLA for instance, it is often 92-95%.  If you print at 100%, you will get over extrusion, and it is more likely threads won't mate properly.  Pretty sure Subscriber has designed these with enough "looseness" that they will fit dang near perfectly on a properly tuned printer.

Hope this helps and doesn't come off as too preachy.  Just want to stress that these are pretty precise objects to be printed, and the printer should at least get some basic tuning to get them printing well.  Maybe someday they will be smart enough, and as easy to use as a dishwasher, but today, they still need some help from the operator.

[WobblyHand]

A 2mm pitch thread would be fine for this part, that would give 3 threads which is enough.  Having 6 plastic threads doesn't buy any strength.  The coarser thread would be easier to clean and to thread on.

Got a second baffle part to print.  I am either going to have to use lithium grease or teflon tape, these things don't want to screw together.  The friction is too high.  The pieces jam up.  Rather use the grease since it is more or less reusable, albeit a little messy.  Teflon tape is a one shot wonder.  I have been working them, but they still are catching a lot.  Going to grease them.

[subscriber]

Bob and Bruce,


Thanks for suggesting printer tuning, Bob.  I was trying to figure out how to do this tactfully, without undermining the satisfaction and enthusiasm that Bruce has gained from his early level of success.


Bruce,

The extension tube you have already printed can serve as an indicator for how well your printer setup is matching internal and external diameters:   
ID = 43.4 mm 
OD = 51.4 mm

Just use a caliper such that the "beak" steps over the inside edge to avoid potential flare there.  Place the relieved notch at the wide end of the caliper beaks so it avoids reading a potential burr or flash at the bottom edge of the ID.

If the ID of your as printed part is smaller than spec by more than 0.4 mm, then I would expect the threads to start getting tight.  Especially if the OD is also oversize.  I think that if you print more than one part at a time, the extruder jumping from one part to the next may also add roughness that might add OD/ID interference.

Attached are a few short cylindrical test prints - STLs are attached.  You will notice that the smaller IDs prints "shrink" more than the larger ones; while the OD errors might diminish as the size goes down.  Or your printer may do something else - hence the value of printing them, so that you can manage the critical features better by means of printer settings.  I added a small chamfer at the top and bottom of the cylinders to hopefully counter the spreading seen where the part meets the platen.  You may still need to run a file around the inside edges to ensure you are measuring the ID and not "flash" at the edge.


Bob,

The shape of the Maxim toroidal spirals is intended to drive smooth, "organized turbulence".    I think that some level of roughness on the surface will actually improve flow, the way a rough shark skin improved bulk flow by creating many small Eddies, that work like a bed of ball bearings to "lubricate" the bulk flow.  Think dimples on a golf ball.

If the internal concave curves sag to the point of becoming straight, that should not cause any trouble with the bulk flow of air.  If the sag turns the flat or concave surfaces into a more than slightly convex shape, then the flow may separate from the plastic surface and bounce when meeting the next curve.  That oscillation may produce a vibration in the plastic with an audible component, although the initial speed of the air buzzing around the spiral should produce mostly ultrasound.

Next time I design a thread for 3D printing I will use a 2 mm pitch so one can shave more off, without compromising useful thread overlap.  Apart from the 1/2 20 thread, the custom thread holding the segments together has a 1.5 mm pitch.

[subscriber]

Printed threads have a rougher texture than cut threads. Usually just working them against each other a few times will loosen them.

Sometimes, I'll lightly sand the male threads to knock off any minor imperfections.

Thanks, Stan

I wonder if a wire brush of the right stiffness could be used to reach into the space between thread flanks?  Not something so aggressive that it removes the thread, but on the order of a stiff toothbrush, with more "cleaning power", that does not dull after a little use.

[WobblyHand]

@subscriber took me a while before I understood what you were talking about.  I measure 51.43mm on the smooth OD of the tube and 43.2mm on the smooth ID.  At first I thought you wanted me to measure the male and female threads...  That's not far off.