Marco,I don't consider myself as skilled or as efficient as a proper design engineer. Most of my working life, I had real designers working for me. That said, I tackle everything as if I am being paid for it. I am very much an ideas guy. Actual scale 3D CAD design just helps me to implement and evaluate spatial concepts in a way that is hard to do in one's mind alone.I have developed many shortcuts to design, that might be possible in your design packages. For instance, I place more than one part in an assembly, then merge them into one body before saving as an STL. As long as two parts actually contact each other it is possible to seamlessly merge them into one part. While I designed the above 36 x 1 mm thread from scratch, I will often go to the McMaster-Carr site and download a nut or stud as a shortcut for the thread. Even so, I merged my 36 x 1 mm threaded sleeve, just like I do for imported nuts and studs.That nut or stud is then "turned down", "bored out" or "milled" shorter in CAD to fit the custom design that required the thread. Then the borrowed threaded part is added to the assembly, merged into one body and saved as an STL. When saving the assembly as an STL, Solidworks asks if you want all bodies included. If the parts make contact or share some of the same volume, the original part boundaries are buried in the STL seamlessly. This is similar to movable assemblies printed together in one "part", except rather than actual clearance between parts in the STL, there is contact or overlap.I generally take such borrowed threads and shave 0.1 mm off their flanks, OD and root diameter for 3D printing. Else, the threads are too tight.I can see that your Evanix pistol needs help. It is likely that its muzzle pressure is higher than the rifle, even if the volume of air that needs handling is less. Your red line sketch should work to make a useful difference. Printing a thread with a 1 mm pitch over 10 mm OD is still "easy". My suggestion is that you explore how to do that. Threading only the "cap" from just ahead of the barrel muzzle would enable you to slip in a length of cheap plastic tube to cover the holes in the rear of the shroud, with just a short printed cap to block off flow around the barrel. Else, you end up with a tall narrow print, if you combine all features into one.My biggest concern is the strength of the thread, and that the insert may blow off as a slow moving projectile. Now, I have used light friction to keep baffles in a 30 FPE .22 PCP, fully expecting them to go flying on the first shot. I was surprised by how little they moved on a single shot. My point is that the thread may not work as hard as we assume. Yes, larger calibers and higher pressures will generate more force; but a larger diameter thread has more area engaged.It would be easy to print something to evaluate the thread strength. See image below. In concept it would be a part with the intended wall thickness and diameter, but with the forward exit (1) completely blocked off, leaving only the reflex space open to dissipate air pressure. Or, with both (1) and (2) blocked off, for a worst case strength test. Obviously the test would be via dry firing, as a projectile will punch its way out of the front...If such a dry fire test with just the front (1) blocked off did not strip the plastic thread, then shooting one with a hole should be OK. The projectile is a loose "fit" in that hole and is moving fast, so not an equivalent plug. If you did such a dry fire plugged endcap test, I would point it at a trap from close by, until the pressure (no doubt a hiss) subsided. There is no O-ring at the thread, so there is at least a slow leak path. If you keep the reflex vents open, the leak around the barrel at the rear is significant (on top of the shroud expansion volume to diminish the pressure).It is possible that the endcap might blow off after a one or two second delay. You certainly do not want to open the breech while the barrel is under pressure; nor allow the airgun to point casually. If the endcap flies off, it will not have as much energy as the projectile normally would, because the latter has the full barrel length to accelerate in - compared to the elongation of the material as it fractures (not much). Still, the cap blowing off has the potential to cause a bruise, an eye injury, or break something fragile - such as a window or light bulb or tube. Also, to potentially cause a scare that might undermine confidence in airguns in general, if the delayed event is not managed appropriately.While my designs posted to this thread are motivated by your project, they are obviously available for anyone to print or modify into something else. I am aware that creating detailed "solutions" may not meet your goals, or if they do, may rob you of the satisfaction of making and using your own designs. So, perhaps helping you figure out how to design aspects for printing that seem daunting, would be more useful to you. It is just that doing a design seems the most convincing way of demonstrating that it can be done....I don't use TinkerCAD or Fusion 360, but believe that you can find youtube video tutorials for almost anything. I find tutorial videos for Solidworks when I am stuck. I also have no problems finding or generating unofficial design shortcuts that would enable me to generate models of my ideas. Some of those shortcuts are probably also possible with other CAD packages. Merging parts into one piece is not actually a cheat in Solidworks. There is an official function to do that. Using that to add threads is a bit of a cheat, but who is complaining.So, if you can tell me the endcap thread diameter and pitch I can design you a threaded sleeve that you can merge into your part design. Else, you may be able to add screws radially to hold your baffle stack in place. Similar to how valve bodies are contained.
For the Rex P, A threaded insert is not needed. One detailed that didn’t come across was that the outer decorative shroud has a screw on collar that acts to center the inner shroud. that collar can be used to retain the sleeve and baffles.
This burst disc has a 3,000 psi working pressure and a 5,000psi blow.
Phil,I failed to make it clear that tube radial burst strength for a given material is proportional to the wall thickness and the inside diameter. While axial endcap retention strength is proportional to the wall thickness and the square of the inside diameter.Thus, small diameter tubes fail in radial bursting before they fail axially; whereas after tube diameter reaches something like 2", axial thrust considerations may be the limiting factor. For even larger tube diameters, axial thrust dominates because D x D is always more than D. What also matters is that the resisting material areas also increase linearly for radial bursting, and based on the square of the ID and OD for endcap being blown off.You asked specifically about 1.5 mm wall aluminum tubing. That wall thickness has only a few listings in McMaster, but look at (deleting external links, which I can't post)The tubes in the sketch below, "A" shows material area resisting the radial bursting in red. The blue area in "B" shows the area applied for gas to act on, trying to cause radial rupture. "C" shows the resisting area to axial failure in red, with blue representing the area gas acts on to rupture the tube end to end. I usually calculate safe working pressures from first principles in Excel, but am too lazy to do that right now. My post in a few pages back included such calculations, but it is not laid out to teach based on only the attached image. It would make more sense if explored as an active spreadsheet.
Phil,You are lucky you can model threads. My basic version of SW does not have that ability. I have to model threads or import them.