Concur with the octagonal passages, disagree with splitting it into quarters. Splitting the cannon directly along the plane of the magazine introduces a very large joint that is a potential weak point, requires significant effort to seal, and may cause problems from whatever you use to seal it. Even solvent-welding isn't certain, because you can still get ooze that blocks the passage after you've inspected the part for satisfactory printing. Not worth it, just design passages that print better (hexagon/octagon helps) and use a larger ID if necessary. Also, if you're doing this much printing, it may be worth looking at your own 3d printer. Printing at a local shop is fine if you're doing small scale, but going through a complete development cycle on a complex ship like the Surcouf is a lot of print time. Imagine how much nicer it would be to print overnight or while you're at work.
I gotchu bro. Hey Justin's Wife! Did you know that you can get a decent 3d printer from Amazon for $300 or less? Just think of how much more time Justin will have to spend with you instead of driving away to that stuffy shop place all the time. And you know what holiday is coming up, right? Plus there's all the other things Justin could print, like moustaches, tentacles, toilet paper holders, and tentacle toilet paper holders. What a deal!
I think you forgot the tentacle moustache toilet paper holder. Or something like that. Man, I totally need, oh, wait, no, I don't.
Update - it shoots! Now I need to make it hit hard. I put the whole assembly under water and noticed I have a lot of leaks around the threads. I wrapped thread tape around all of them, but still have leaks. Looking for suggestions…. Do I have the wrong type of threads?
I use 1/4-20 threads for the magazine loading port, with an o-ring to seal it. Very tight, works good. The opening with the piston uses 1/8NPT, and I use acetone to seal the threads to the fitting. Also very tight. Lastly, the breech itself has a nice fat o-ring squished between the barrel and the breech fitting, which seals very well there. The cannon as a whole still loses pressure over several seconds, but it certainly gets enough pressure to fire quite hard.
Cannons Mk6 - Updates: - Mk5 had a hairline crack in the main structure from screwing in the rifles; so I thickened the superstructure by almost 0.1" - I removed one loop on the magazine for better loading - I lengthened the length of the magazine to take advantage of the increased thickness. - I added an 0-ring to seal the magazine loading bolt. - I will seal the chamber bolt with lock-tight, because there just isn't much space down there. - I moved the chamber air exhaust higher, to push the piston out of the way before the air can escape down the magazine.
Update - the O-ring worked out well, and the new BB tube fed really well. Unfortunately the threaded clippard nipple keeps splitting the base. I’m going back to gluing in a simple straight metal tube. Also the threads bound up and broke the barrel nut this time. So, today I watched a bunch of tutorials on how to get 3D threads to behave. After running a number of prints, I think I have the method that works best for the TAZ. I also bought transparent PETG, so I can see what’s working vs not. Taz is in process of printing mk7.
Good luck with the PETG. You can't vapor-weld it with acetone, you have to use MEK which is REALLY nasty. So you'll be stuck with micro-leaks throughout the cannon. You're probably not set up for large-scale ABS printing yet, but you should be working towards that. I have also tried printing in clear plastics, and the result was not super-useful. It was barely translucent, and I needed a 240fps high-speed video to see the firing sequence. In the end the resolution was too low and the lighting too bad for me to learn anything useful from it.
I tried PETG. You -can- make it work… but definitely not worth the effort. I sealed mine with plastic cement that contained MEK. I do have straight MEK for powdercoating. I try to avoid using it unless I have to because it WILL take the skin off your hands of youre not careful (or even if you are and manage to get some inside your gloves… skin flakes off like a bad sunburn) The bond wasnt nearly as strong as it is with ABS and acitone. I was able to test a few hundred rounds before I noticed small voids forming. Eventually I was able to peel the ‘fused’ layer away.
SO FAR - I've been able to print my design in one pass; so no air-tight gluing required. The only glue needed will be between the right and left cannons, which can be CA glue or even screws for all I care... That said.. it's NOT air tight yet. Mk6 had a lot of cracking and air leaks due to the threads, so I can't actually claim victory yet. I'm just starting to play around with Mk7 this morning; but I can tell you the threads are PERFECT. Everything is coming together nicely. I'm having a bit of a jamb issue with the interruptor piston, but I think it's just a simple tolerance issue. I'm double checking all the prints vs Fusion 360, and will come to know soon... but I'm sure it'll be just a re-print of the piston. I'll head over to the hobby shop soon and pick up new brass tube for the air nipple and BBs that fit in the BC rifle. Otherwise, all the previous issues seem to be gone with Mk7 and I have high hopes of the cannon hitting hard today!
Loaded the mk7, and verified it holds exactly a 50 round per cannons. 100 rounds should be plenty for a sub, and probably much more than I have CO2 onboard.
Mk7 has passed all its bench tests… so now time to run to the store and pick up the remaining parts! Mk7 would like to ask everyone to cross their fingers!!
While the transparency is NOT what I had hoped for in terms of visibility. It’s still translucent enough with a light source behind it to see what I need “so far”.
well…. I closed the big leaks and discovered a new type of leak. Any suggestions? Return to ABS & use acetone? I like PETG, am I SOL?
