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All Springer/NP/PCP Air Gun Discussion General => 3D printing and files => Topic started by: wimpie swart on September 07, 2021, 12:28:02 PM
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Hi all,
I hope you all are well.
Question for the 3D experts; would you print a breech from ABS or PETG? If the design lends space for a brass or steel TP, between valve exhaust and barrel, then one would not have to worry about the pressure holding capabilities of the printed part.
Am I in the right thought direction or missing the ball?
Thanks
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ive printed a ton of breeches , but generally as a test run before making it from aluminum.. ( check dimensions and so on) For low pressure guns like pumpers and co2 , pla works fine , as does abs since we know most crosman pistols come with an abs breech.. Its really dependent on how the breech is secured and the fact the load is well distributed during the shot cycle .. ( crosman 1377 breeches arent really taking a direct hit , neither are 2240 plastic breeches or the new 362) the air is channeled from metal part to metal part to barrel. For pcps Scot Hull has used a few for very powerful guns.. Its definately a viable idea
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Thanks Rob, I will be testing my Bam B50 multi shot breech with sidelever.
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Thanks Rob, I will be testing my Bam B50 multi shot breech with sidelever.
post some pics and some feedback when done..
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PLA is stiffer than either ABS or PETG. I've made and used several PLA breeches on Armada/Marauder based rifles at up to 180fpe.
They performed fine. Transfer port tubes were made of brass. PLA does not like high temperatures. I switched to aluminum using a lost PLA process once the design was to my liking.
For something like a bullpup where the breech does not need to support the barrel or scope, I would not have a problem keeping the plastic breech. PLA is fine, but ABS or PETG is probably better for longevity. Any (PLA, ABS, PETG) can work, just design accordingly.
I have found that I get better results doing thread forming in PLA rather than thread cutting on small fasteners. Use the appropriate thread forming hole size and then form the threads using a lubed screw.
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PLA is stiffer than either ABS or PETG. I've made and used several PLA breeches on Armada/Marauder based rifles at up to 180fpe.
They performed fine. Transfer port tubes were made of brass. PLA does not like high temperatures. I switched to aluminum using a lost PLA process once the design was to my liking.
For something like a bullpup where the breech does not need to support the barrel or scope, I would not have a problem keeping the plastic breech. PLA is fine, but ABS or PETG is probably better for longevity. Any (PLA, ABS, PETG) can work, just design accordingly.
I have found that I get better results doing thread forming in PLA rather than thread cutting on small fasteners. Use the appropriate thread forming hole size and then form the threads using a lubed screw.
Thanks so much for your input!!
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Scott, I'm curious about your approach to the lost PLA casting. What do you coat the PLA with? Do you burn out the PLA or let the aluminum do that?
Nice results!
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Scott, I'm curious about your approach to the lost PLA casting. What do you coat the PLA with? Do you burn out the PLA or let the aluminum do that?
Nice results!
I have a friend that does the casting for me. I print the PLA at +1% oversize to account for shrinkage of the aluminum casting. He can do either coating or fill a flask with the investment plaster. The breeches were cast with the vacuum flasks. PLA pattern and sprue is put in the flask and a vacuum pulled while plaster is poured in and vibrated. Then it is cured in a ceramic/pottery furnace and PLA burns out at those temperatures. Clear or natural PLA leaves the least amount of ash but I have used other colors. Aluminum was poured while a vacuum was pulled on the mold. Though it is possible to cast with gravity only with proper sprue/riser/gates.
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Thanks, Like I said, those look great.
....Another hobby to look into. ;D
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Wimpie,
The bending moment due to the barrel trying to droop under gravity would probably be the largest stress on a plastic receiver. I would make the barrel engagement with the receiver long to better support such a moment.
In scanning the above replies, someone mentioned a bullpup (I think). That might have the barrel supported well in at two locations some distance apart. A good idea to reduce creep, if the plastic has no filler material in it:
Many plastic creep at room temperature. Most plastics that contain no filler materials creep above room temperature. PLA is quite stiff, but will creep a lot, especially if exposed to direct sun. Filler materials are used to reduce creep in plastics. Fillers include glass and carbon fiber. I know that carbon fiber 3D printing plastics exist. You did not mention the type of printer, but I am assuming molten filament. If you included SLA or SLS, I think the material choices are even broader, including metals.
You are quite right in making all the parts seeing high pressure air out of something much stronger.
Hoop ek is nie te laat nie :)
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You are quite right in making all the parts seeing high pressure air out of something much stronger.
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Depends on the part/design. I was using printed PLA (100% infill) shuttles in the early testing and it works fine carrying the 3000psi air from the transfer port to the barrel. I have since changed to cast aluminum but had no problems with the PLA version. Here is an image showing a cross section and the air path which makes a 90 degree turn:
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Thanks Scott,
Blanket statements are not as useful as detailed explanations, and I made one; so you helped me out. That said, there is a reason you switched to aluminum for your TP :)
The text below is not meant to "school" you, Scott; it is written for Wimpie's benefit. You clearly know what you are doing. And a lot more than many on this forum:
The fact of the matter is, that it is not air pressure that matters for part strength, but the force that the air applies. That force depends on both the pressure and the area it is applied to. Then that force is carried by an area of material, and a stress results in the material. If the stress is lower than the material yield strength, the parts does not fail - not immediately anyway. If the stress is greater than the material yield strength, the part distorts permanently, even if it does not "blow up". If the stress is greater than the ultimate material strength, the part ruptures immediately.
Filament printed PLA could work for a TP because the internal area is small and the load is only applied for perhaps 0.003 seconds. If you maintained air pressure on such a part, it might show up a slow leak, with air escaping between some poorly fused sections of filament. Or the filaments could tear between welds, separating over time and allow air to leak out. Either precipitating a catastrophic part failure as the crack "runs"; or acting as a safety valve to depressurize the system. If not designed as a failsafe, assume abrupt rupture...
In any event, the energy in the air from one shot is a bit more than what would be imparted to the projectile - perhaps twice as much in some cases. So, for a 20 FPE PCP, the "explosion" in a failing TP might show equivalent part damage of 40 FPE projectile impact. Not something I want my face nearby, but not something that is going to lift the roof off a house.
On the other hand, printing a 3D air tank from PLA would be a very bad idea, because the stored energy that would be released in a rupture could be over 1000 FPE (proportional to the volume of air and its pressure). PLA is surprisingly strong, but very prone to creep (material distortion or "flow" when stressed for a long period - even at room temperature). So, a constant high pressure will "blow" a PLA tank sooner or later - even if the wall is "thick enough" based on simple calculation and a typical factor of safety. Obviously filament wind direction also maters, but discussing that makes it sound as if there is a PLA solution for pressure vessels. There is, but only as a form and fit mock-up. Not as a fully functional part.
Looping this back round to a more sane example; this is why such a thin .22 rimfire case head can be easily indented by the firing pin, yet does not rupture at the unsupported case head periphery, despite the SAAMI peak pressure rating of 24 kPSI: The unsupported area is small.
In other words, the devil is in the details. My first generalization meant, "if you don't understand the details, assume the worst case".
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Subscriber,
In general, your warnings are correct. PLA worked but the aluminum gives me a greater factor of safety, so I did switch.
I would never use PLA in a constant pressure application, as in a pressure vessel. Actually, even though the cast aluminum works fine for breeches, it too has been problematic when attempting to use in constant pressure applications. There always seems to be some micro porosity in the casting that allows pressure to leak.
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Very interesting, Scott
Are you displacing the PLA with molten aluminum; or forming a hard ceramic mold and melting out the plastic first, as is done with wax investment casting?
If the PLA has to be burned out by the molten metal, perhaps that flow restriction and gas generation explains the porosity in your parts. I thought they looked amazingly good for a home process. I wonder if soaking in a resin of some sort could seal the porosity; not that it matters if parts see pressure only during firing.
The ideal way to seal porosity would be to place the receiver in a tub of slow curing low viscosity resin, fully submerged. Then place the tub in a vacuum chamber. After pulling a near total vacuum and letting the chamber sit for 5 to 10 minutes so that the air in the pores can be drawn out, the air inlet to the chamber is slowly opened. That results in atmospheric air pressure forcing the resin into the metal pores, while the resin is still fluid.
The question is how to do the above without using a whole tub of resin that has had the catalyst added. Perhaps the tub can have a close fitting plastic bag around your receiver, that contains a limited volume of resin. Perhaps the resin only needs to painted onto the sections of the part exposed to high pressure air. Anyway, a similar vacuum method is commonly applied to force resin in, after air is drawn out of carbon and glass fiber parts, during manufacture.
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things will get real interesting when we have DMLS printes at home ( metal sintering ) Im guessing another 10 yrs, there will be home machines fo under 10 k.
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I've been looking at lost PLA aluminum casting approaches that don't use a burnout furnace. This guy's approach looks doable and the results are pretty good.
https://www.youtube.com/watch?v=pyZEJRet_8o (https://www.youtube.com/watch?v=pyZEJRet_8o)
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Wow, Stan, that video makes it look easy.
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Lost foam casting might be another option: https://www.youtube.com/channel/UCSTKBcCz9pD_MC0l_ZarxhA/videos (https://www.youtube.com/channel/UCSTKBcCz9pD_MC0l_ZarxhA/videos)
https://www.youtube.com/watch?v=AUun6vgPJcQ (https://www.youtube.com/watch?v=AUun6vgPJcQ)
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Thanks, Very impressive, especially the shapes he creates and assembles using routing patterns. I was hoping to be lazy and 3D print the pattern. ;D
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I was hoping to be lazy and 3D print the pattern. ;D
A perfectly good plan.
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Heat treat your guns? Maybe not like they did with the 1903s (PB) a few times till they got it right... then started doing it another way.
How about heat treating PLA?
Start with a higher grade high temp plastic and anneal. It has to be better than relying on the print nozzle to fuse hot to already cooled.
https://www.pushplastic.com/products/premium-pla (https://www.pushplastic.com/products/premium-pla)
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Heat treat your guns? Maybe not like they did with the 1903s (PB) a few times till they got it right... then started doing it another way.
How about heat treating PLA?
Start with a higher grade high temp plastic and anneal. It has to be better than relying on the print nozzle to fuse hot to already cooled.
https://www.pushplastic.com/products/premium-pla (https://www.pushplastic.com/products/premium-pla)
When the slicer and printer are setup correctly, the PLA parts have near 100% consolidation. Typically good to go.
If one still wants to "heat treat" or "anneal" PLA parts after printing, I would recommend packing in sand prior to doing so. Unsupported PLA can easily lose it's shape when heated any significant amount.
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From my understanding, heat treating 3D prints is only done to relieve internal stresses and not for adhesion.
Dave
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MrP on this forum paints his 3D prints with epoxy resin to strengthen them. The rougher and more porous the print, the more resin it absorbs.
Of course, if you can print parts such that their strength is nearly the same across and along the filament, then little after treatment should be required.
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Thank you one and all; for your input to this thread!!!
Somebody asked; I am using a Creality Ender 3 Pro as well as a Creality Ender 3 V2.
Will have to bench this project for a while, other priorities have taken residence.
I will be discussing aluminium casting with a local guy here, at a later stage.