Kotori87 submitted a new resource: 3dp Coil Sidemount - Tightly coiled sidemount with 20 degree down-angle, and printed compression nut for barrel Read more about this resource...
So the 9 compression nuts in the file... I'm assuming the internal diameter is slightly different so you can get a good match to your printer? Do you print the nut separately and weld together after printing, or do you join it with the magazine and print as one piece? I am intrigued with making the nut part of the gun. It eliminates the glue joint between the tube and the magazine, which always concerns me. So I see it having application to the BIC or LPC style cannons.
Good questions. You are correct, the different compression nuts have slightly different thread sizes, so you can get a good match. I don't like wobbly barrels that need support near the tip, so I want a fit that's tight enough for cantilever barrels, but loose enough that I can do coarse adjustments by hand. It also needs to be printed separately for best results. I have found that fine threads like 1/8NPT or 1/4 compression don't print well unless they're oriented vertically (or near enough to it). Separating the nut allows me to print all my parts with a good orientation for the threads, and then solvent-weld it together afterwards. It does also eliminate the glue joint, an area I have had trouble with before. I can't take full credit for the idea, though: I think it was Brian who thought up the idea of putting the nut on the cannon and the threads on the barrel. I just made the nut 3d-printed after my first attempt to glue a brass nut in place with epoxy leaked.
Is there a breach and piston for this somewhere, or are you using a different print for those, or using other parts for actually firing the BB?
The T-fitting is built into the main cannon body. The o-ring seat (what most folks call the breech) is a separate 3d-printed part that gets solvent-welded in to the main cannon body. The piston is a 1/2" stainless steel rivet from Mcmaster-Carr, with the rivet head turned down on my lathe. I have also tested injection-molded plastic pistons and those worked well, but Strike Models stopped producing them several years ago so I can't get more. I have not tried 3d-printed pistons. I have a bunch of the stainless rivets, so that's what I went with.
Thank you for the reply! Is this kind of what is what? haha I started typing these out and thought it would be easier to see in picture form. Do I have these right?
Oh and one more question, what do you use to keep the piston in place here? Did I miss another print file? thanks again for the feedback!
Test print from several months ago. Final assembly, ready for test firing. The printed nut has been solvent-welded in place, magnet installed at the tee, piston and spring assembly installed and sealed, barrel and fresh o-ring installed, and magazine loaded and capped. The bottom of the cannon has a 1/8NPT female thread, so you can use a wide variety of air fittings. This prototype was equipped with a Clippard swivel 90-degree fitting, since I have a bunch. The ones I installed in my predreads used 1/4" push-to-connect fittings so they could drop straight down into the barbette, onto a waiting hose sticking straight up from the solenoid in the bottom of the ship. The magazine port uses a half-inch long 1/4-20 hex-head bolt and an o-ring to seal. I don't remember exactly what size o-ring, I just test-fitted a few options from the local hardware store until I found one that fit. You are correct about how the nut and cannon body fit together. The barrel is installed with a male 1/4" compression threaded fitting from the local hardware store. I reamed it out a little to fit the barrel, but otherwise it is stock. Other production notes: The ABS I commonly print in requires acetone treatment to get a fully airtight seal, otherwise you'll have little micro-leaks bubbling through the layers when you tweak it really hard. After solvent-welding the printed nut in place, I put thread protectors in all of the threaded portions of the cannon body, then brush the entire exterior of the cannon with acetone for about a minute. This leaves the cannon well-sealed, but with a terrible finish. I follow that with a short 5-minute vapor bath that clears things up very nicely. Since not all 3d printers are perfect, you may have to do a little cleanup with a drill bit to ensure a bb will roll all the way through the cannon. If your printer is struggling with the inaccessible spiral part of the magazine, let me know and I can adjust the dimensions of that pathway for you. The one thing I cannot tweak is the size of the threads. Unfortunately Fusion360 has no good way to oversize threads, so I have to clean up the printed threads with a tap to ensure everything works well. One thing I discovered with male-threaded barrels like this is that it is very important to get the threads properly co-axial with the barrel itself. If they aren't aligned right, the barrel will wobble up and down as you adjust your tweak, which messes with your aim. My earliest test barrels just had cut-off bits from various 1/4 compression tees I'd hacked up, and the results were less than satisfactory. I found that using the full length of a male-to-male coupling, like shown here, provides sufficient alignment.
I hadn't looked at this too hard until I saw the pics above. This design is great! Simple and efficient use of material. Nicely done, sir!
