Slim LDC

[WobblyHand]

Designed and printed a slimmer version of an LDC.  Designed it to fit inside of a CF tube with OD 25mm, and ID 22mm.  Based it on @subscriber 's Notos design.  It is 6.5" long with a 1/2-20 thread.  I need to test this thing - definitely for a low power AG, I designed it for a 2240.  Still need to make the adapter to fit on my 2240 - I'll machine the adapter out of steel in the next couple of days.  Printed in black PETG, which photographs terribly.  First check showed a 1/4" rod didn't go through, which is kind of expected with 3d printing.  A quick pass of a 1/4" reamer fixed that.  Used a 1/2-20 tap to clean up the threads.  And miraculously, the insert is a nice snug, almost difficult fit in the carbon fiber tube.  I'll get some pics in the morning.  For the test fire, I won't use the sleeve.  I've never tried this before, so I'm expecting some sort of mayhem.

[WobblyHand]

Here's a picture of the CF tube, the LDC, that I mentioned in the previous post, along with an adapter I made this afternoon.  The adapter is made of 1144 (Stressproof) steel, because, well that is what I had in that size.  Not complaining, it machines very well.  The threads fit the LDC.  The adapter just barely slides on to the 2240 barrel.  Very nice fit.  I need to add a set screw to the adapter, so it won't blow/fall off.  The set screw will engage the flat of the barrel. 

Think the next adapter will be from a larger diameter rod, so the LDC has a larger area to seat against.  Live and learn.

[WobblyHand]

Here it is mounted on the 2240.  Need some CO2 cartridges to try this out.

Edit: just ordered some.  They will be ready for pickup tomorrow.

[subscriber]

Nifty, Bruce

Is the bore .25 for a .22 pellet?  Seems tight enough that slight misalignment may cause a "prang".  If that happens you can make another version.

[WobblyHand]

It has a .25 cal bore, at least after I passed a 0.2500" reamer through it.  As printed, it was not quite 0.25 cal, a 0.250 rod wouldn't go through it. I have to check to see if I have any larger size reamers.  Bought a lot of reamers a while back,  maybe I have something slightly wider. 

Depends on how "brave" I am today.  Might try it out on my 1377 first, have a little more margin for error for clipping and I can adjust the number of pumps.

[subscriber]

I design baffle bores to open up in steps towards the front.  So, getting the least blow-by at the start, with lower risk of clipping near the front end.  Something easily done in single insert design rather than multiple stackable baffles.   Then you would need to keep track of which goes where.  Possible, but a nuisance.

You could add features that force the order of the individual baffles in a stack, but that seems like a lot of work, when combining them into longer sections seems so easy.

[WobblyHand]

I design baffle bores to open up in steps towards the front.  So, getting the least blow-by at the start, with lower risk of clipping near the front end.  Something easily done in single insert design rather than multiple stackable baffles.   Then you would need to keep track of which goes where.  Possible, but a nuisance.

You could add features that force the order of the individual baffles in a stack, but that seems like a lot of work, when combining them into longer sections seems so easy.

That's a good idea.  Next one I design will have a slight outward taper in the bore.  That and a slightly larger adapter face to seat against.  In the end, though, one is fighting gravity and relying on the stiffness of the material to prevent sagging and clipping.

Still don't know how to force constraints on the slicer, so that key constraints are met.  Seems like the process is print, fiddle, print, fiddle, ... With long prints that seems inefficient. 

[TorqueMaster]

...
Still don't know how to force constraints on the slicer, so that key constraints are met.  Seems like the process is print, fiddle, print, fiddle, ... With long prints that seems inefficient.

Key constraints as in key dimensions, or something else?  Are you using Cura?  Either way I can offer specific or generic suggestions if you're interested.  Sometimes it is try, fail, modify, repeat...sometimes the first educated guess actually works!

[WobblyHand]

...
Still don't know how to force constraints on the slicer, so that key constraints are met.  Seems like the process is print, fiddle, print, fiddle, ... With long prints that seems inefficient.

Key constraints as in key dimensions, or something else?  Are you using Cura?  Either way I can offer specific or generic suggestions if you're interested.  Sometimes it is try, fail, modify, repeat...sometimes the first educated guess actually works!

Key dimensions.  I'm using Prusaslicer.  I've been burned before on this try, fail, modify cycle a few (more than a few) times.  I don't mind on a 20 minute print, but on significantly longer print times, it's a pain.  Sometimes the bore is critical, sometimes the exterior, sometimes both.  I do realize it is a 3d printer and I'm dealing with plastic, but, you'd think there would be some knobs to control in the slicer.  There probably are - but I don't know what they are called.

Must have got lucky, my LDC came out ok.  I did run a 0.2500" reamer down it.  Did some test firing on a 1377 and 1322 and no disaster happened.  Haven't tried it on the 2240 yet, but I'm hoping my luck continues...

[dan_house]

big prints.... can be broken down into smaller "bites" that dont take as long

depending on where the bits in question are, you can do some of that in your slicer

[subscriber]

Bruce,

If you are talking about a self supporting structure, then I taper the outer wall thickness from "heavy" at the rear, to "thin" at the front.  This makes sense to resist bending, and maintains sufficient burst resistance.

How heavy depends on the OD and length, and my estimate of muzzle pressure, based on FPE.  For a snug fitting insert, supported by a stronger outer tube, the outer wall of the insert can be made much thinner.

For my design you mentioned in the OP, I made the outer wall taper from 4 to 3 mm.  Could probably taper it down to 2 mm without any problems, assuming properly printed PETG.  The lighter the front, the less hard the rear has to work to prevent droop.

If you are using PLA, chances are that the material will creep over time, because that is the nature of PLA.

For the bore, I like a radial gap of 1 mm over pellet diameter.  Then increase that going towards the front by an additional 0.1 mm every 25 mm.  In some cases I might make it tighter, or looser, depending on confidence in concentricity and angularity relative to the barrel bore.

[dan_house]

Key constraints as in key dimensions, or something else?  Are you using Cura?  Either way I can offer specific or generic suggestions if you're interested.  Sometimes it is try, fail, modify, repeat...sometimes the first educated guess actually works!

Im interested..... Ive been using print/test/redraw for a long time, and if some or all of that could done in my slicer (Cura) then even better

[subscriber]

big prints.... can be broken down into smaller "bites" that dont take as long

depending on where the bits in question are, you can do some of that in your slicer

You can design a deliberate split into the part.  I designed an insert 13" long for Don (NVreloader).  I designed it as three separate parts that butt up against each other inside his super long shroud.  If your printed part is not an insert, but has to rely on its own stiffness, then how to join them takes a bit more consideration.

[subscriber]

Dan,

Printing short section of the design containing the critical dimension to measure helps a lot.  Bob is an expert at that. 

I have created short generic test prints that might be useful for general calibration:  https://www.gatewaytoairguns.org/GTA/index.php?topic=204046.0

[dan_house]

"then how to join them takes a bit more consideration."

ok, wasnt clear....

I should have said "for test printing purposes"....

I have a design for a "chassis system" for the Diana Chaser. I cut the part of the chassis that had the trigger inletting away from the rest (in my cad program), printed and test fit that piece to the trigger block. Changed the drawing, and repeated that. Then repeated that process until the backbone of the chassis fit correctly.  While that did take a couple of evenings, the end result was a part that fit the chaser correctly the first time the whole part was printed.

Once I had that part functioning correctly the rest of the design was a piece of cake

[dan_house]

Dan,

Printing short section of the design containing the critical dimension to measure helps a lot.  Bob is an expert at that. 

I have created short generic test prints that might be useful for general calibration:  https://www.gatewaytoairguns.org/GTA/index.php?topic=204046.0

Oh man how did I miss that??

Thank you sir!!

[subscriber]

Thanks for the clarification, Dan

Obviously one can design one's own test prints that are closer to your design intent.  Possibly with features stripped away that might be in the way for measurement - if simply cutting it short does not provide access.

Looking at my test print menu, the round on with the 8 mm diameter bore is probably most pertinent to the OP's needs; along with the next size up.   It may be that more test print about that size are prudent.

Certainly, if one is printing threads that you intend to use without chasing, then having test prints for that would be useful.  With Bob's help, I have developed a feel for how much clearance to add to threads in CAD. 

That said, threads with a pitch smaller than 1 mm probably should be chased.  Especially if the nominal diameter is below 12 mm.  But then taps in the 3 to 12 mm diameter range are common and not expensive.   Taps much over 1/2" can get expensive, if it is for one time use.  And dies are much more expensive, but one could make a functional die to chase plastic thread from a steel nut.  Many taps and dies can be ordered from China at more reasonable cost.

[TorqueMaster]

Key constraints as in key dimensions, or something else?  Are you using Cura?  Either way I can offer specific or generic suggestions if you're interested.  Sometimes it is try, fail, modify, repeat...sometimes the first educated guess actually works!

Im interested..... Ive been using print/test/redraw for a long time, and if some or all of that could done in my slicer (Cura) then even better

Whoops, I meant to address this to OP, but should apply to Dan as well.

I've heard mostly good things about Prusaslicer, so it's probably fine.  Most of these tips are generic.
Ok, you mentioned interior and exterior dimensions. 

Exterior is all about printer calibration.  On some printers, the XY steps/mm may need tweaking, but I've found on my cogged-belt driven printer, it's never needed adjusting.  There is some unavoidable slop, but usually less than 0.1mm, so usually negligible.  Next is making sure the extruder feeds exactly as much filament as requested-- call for 100mm, then 100mm should feed into the extruder.  Some do it with the hot-end removed, some do it through the hot end, whichever, be consistent.  Then tuning flow percent will help some -- I print a 2-line wide wall (0.4mm nozzle, 0.4mm linewidth), that should measure/average 0.80mm at it's topmost layers.  Adjust flow % as needed to get there.  That gets very close.  Sometimes I print 10mm cubes until they have no measurable bulges or excess height to further gnat's @@@ the flow setting.  I should say a calipers that does 0.01mm resolution is almost essential.

Once calibration is tweaked, interior dimensions should also be pretty close.  The biggest exception is smaller interior holes, especially circles, printed in the XY plane.  The filament tends to stick and create smaller holes than expected.  The tinier the hole, the bigger the problem -- any under 0.5mm usually disappear completely.  Designing hole diameters larger than needed (on the order of one-half-to-one nozzle size bigger) can get you close.  Or plan on drilling to size.  Or Cura has a "hole expansion" option that may fix them without munging other dimensions -- I haven't tried it.  I also read somewhere that using hexagons or octagons instead of circles -- with straight rather than curved walls -- reduces this hole shrinkage issue.  I haven't tested that yet.

Someone mentioned printing select slices of your object -- rather than the whole thing -- to test critical dimensions -- very useful and time saving.  Chop it up in your cad, or I use tinkercad, to just that area.  Also, Cura lets you place an object at negative Z relative to the print surface, so the layers you don't want are under the surface, and not printed, and then you can stop the print after 10-20 layers, and take measurements, adjust the design, reprint.... 

Hope this helps.

[WobblyHand]

First shot through the LDC on my 2240 and it is quieter.  No one is home, so I tried it without the LDC.  I need to put the gun in a vise, and do a with and without for POI, but so far, so good.  Simultaneously added an SSG.  It's not dialed in, but it's functioning at some level.  A good day.

[WobblyHand]

Key constraints as in key dimensions, or something else?  Are you using Cura?  Either way I can offer specific or generic suggestions if you're interested.  Sometimes it is try, fail, modify, repeat...sometimes the first educated guess actually works!

Im interested..... Ive been using print/test/redraw for a long time, and if some or all of that could done in my slicer (Cura) then even better

Whoops, I meant to address this to OP, but should apply to Dan as well.

I've heard mostly good things about Prusaslicer, so it's probably fine.  Most of these tips are generic.
Ok, you mentioned interior and exterior dimensions. 

Exterior is all about printer calibration.  On some printers, the XY steps/mm may need tweaking, but I've found on my cogged-belt driven printer, it's never needed adjusting.  There is some unavoidable slop, but usually less than 0.1mm, so usually negligible.  Next is making sure the extruder feeds exactly as much filament as requested-- call for 100mm, then 100mm should feed into the extruder.  Some do it with the hot-end removed, some do it through the hot end, whichever, be consistent.  Then tuning flow percent will help some -- I print a 2-line wide wall (0.4mm nozzle, 0.4mm linewidth), that should measure/average 0.80mm at it's topmost layers.  Adjust flow % as needed to get there.  That gets very close.  Sometimes I print 10mm cubes until they have no measurable bulges or excess height to further gnat's @@@ the flow setting.  I should say a calipers that does 0.01mm resolution is almost essential.

Once calibration is tweaked, interior dimensions should also be pretty close.  The biggest exception is smaller interior holes, especially circles, printed in the XY plane.  The filament tends to stick and create smaller holes than expected.  The tinier the hole, the bigger the problem -- any under 0.5mm usually disappear completely.  Designing hole diameters larger than needed (on the order of one-half-to-one nozzle size bigger) can get you close.  Or plan on drilling to size.  Or Cura has a "hole expansion" option that may fix them without munging other dimensions -- I haven't tried it.  I also read somewhere that using hexagons or octagons instead of circles -- with straight rather than curved walls -- reduces this hole shrinkage issue.  I haven't tested that yet.

Someone mentioned printing select slices of your object -- rather than the whole thing -- to test critical dimensions -- very useful and time saving.  Chop it up in your cad, or I use tinkercad, to just that area.  Also, Cura lets you place an object at negative Z relative to the print surface, so the layers you don't want are under the surface, and not printed, and then you can stop the print after 10-20 layers, and take measurements, adjust the design, reprint.... 

Hope this helps.

Some of this is simply expectations.  Since I can and do machine, I don't consider an error of 0.1mm to be good at all.  Being off by 0.004" isn't very good, when I machine, I often do much better than that, especially on bores. 

I do need to do further calibration.  Actually, I need to level flatten the bed - which I have been putting off.  I have the little nylock nuts, just need to figure out how to rig up a good dial indicator on the print head to measure the bed hot, to come up with settings.

Thanks for the tips on the hole size adjustment, that is helpful.

I've printed some stuff that didn't fit, particularly on inside dimensions.  Made a DRO read head bracket that was shaped like a U, the read head was supposed to be a tight fit inside the U, and had a devil of a time fitting the read head in without excess slop.  3d printing is pretty cool, but the consumer stuff is somewhat limited.