This is a break-out thread from my Surcouf thread, located here: https://rcwarshipcombat.com/threads/french-submarine-surcouf.447110/ --- I decided to walk away from the BC cannons I bought for several reasons (mostly weight and size). I'm going to try my hand at 3D printed guns. If they work, then I want to upscale them to Big Gun calibers in future revisions. My concept is simple, try to keep with the BC gun dimensions as closely as I can. I've never 3D printed cannons before, so I'm open to any/all recommendations. I downloaded & re-re-reviewed Greg's upgraded cannons, but unfortunately I couldn't really wrap my head around them. I just can't understand the magnetic / non-interrupter style cannons (yet). SO, I decided to start with what I know and iterate from there. The biggest concern I have is the bottom plug. I don't know how thick I'll need to keep it in place, but it's pretty thin (0.01")... however that's enough to take a 1/4" bearing impact. The part that I'm the least happy about is the overhang in the bottom. It does fit in the ship; however it means I need to do some sort of support 3D print support structure. This bothers me because I'm sure the slicer is going to add supports in areas I don't want. I'm trying to think of a way to remove that overhang as my top priority. Anyway, here is the full structure, ready to print!
I'd recommend not using supports at all. I'd lay that on it's side and cut it half and then cut it again on the barrel center line. To save time, just iterate on half of this assembly until you are satisfied with the design.
I'd avoid using circular profiles for the interior passages. They require one to really dial in the printer, use thin layers, and spend extra time printing in order to get good results. Octagonal cross sections are *MUCH* easier to print in any orientation. Any features that need to be round can be printed under sized and finished up with a drill bit and a reamer. Also, those internally threaded features may work better as separate parts.
So now bring that into your slicer and cut it on the plane of the barrel center line. Orient those parts so the internal passages are on the print bed. You shouldn't need any supports, especially if you use octagons. PS. You may want to design in holes for alignment pins. That'll make gluing them easier, later.
Use an octagonal prism to difference them from your model. Print those vertically, run a tap through them if needed, and then glue them in. Or borrow the similar parts that @Kotori87 has posted. They are hexagonal so not quite as versatile but, there for the taking : )
One of the nice things about 3d-printed cannons is you can contort them in ways that traditionally-built cannons simply cannot do. That said, you need to be smart about how you arrange your cannons. Here are some lessons I've learned from my 3d-printing experiences. 1) print cannons in ABS. You MUST be able to solvent-weld parts together, solvent-smooth the surfaces, etc. The solvent-smoothing is particularly important to solvent-smooth the surfaces of the cannon to seal it pressure-tight. The normal layer adhesion of 3d prints is good enough for structural strength, but it is not pressure-tight. Unless you want leaky cannons, they must be thoroughly solvent-smoothed. 2) print the cannon in several parts, so you can place parts on the print bed in the optimum orientation. For example, my LPC cannons have three separate threads apiece. One 1/8NPT thread on the bottom for the gas fitting, one 1/4-20 thread on the top for the magazine fill port, and one 1/4 compression fitting on the front for the barrel/breech assembly. The first two threads are oriented vertically, so I can easily print them as part of the main cannon. The compression fitting is horizontal though, which does not print well in that orientation. So I print it separately in a vertical orientation, then solvent-weld it in. My current crop of cannons using this method have been through more than two years of hard fighting in several ships, and there is no sign of failure or deterioration. 3) smooth curves are extremely important for proper feeding. The larger the radius of your corners, the better it will feed. Changes as small as 0.5mm can have a significant effect on the reliability of your cannons. I know your sub doesn't need to do 10 rounds per second at 280FPS, but right now your magazine has square corners, no slope, and no magnet. Each of these make a big difference. 4) Details matter. A single tiny blob of plastic in just the right spot can be the difference between a perfect cannon and one that needs a good whack every 5 rounds to keep operating. I get better print results for my Fast Gun cannons at one room temperature, and better print results for my Big Gun cannons at a different room temperature. Greg designs his cannons essentially layer-by-layer to ensure optimum performance with his particular printer and slicer. Using too weak of a magnet may cause feed issues, but using too strong of a magnet may cause different feed issues. Be prepared to iterate on your design A LOT as you test, tweak, and fix flaws. Don't be afraid to cut apart both failed and functioning cannons to see what works and what doesn't. 5) don't use 3d-printed pistons. I found they were far too weak. 6) my LPCs and other 3d-printed cannons have three different diameters around the piston. There's an area for the head of the piston to sit and move up and down. There's an area for the spring to fit, fully compressed. And there's an area for the tip of the piston to slide up and down in. The first and last are pretty self-explanatory, but the second one I found was important to prevent jamming the spring into layer lines or other problems, and it also helped keep the piston itself straight so it couldn't get cocked and jammed. I also beveled the transitions between these different areas, so I wouldn't need to add (and later remove) supports to print properly. If you're interested, drop me a PM and I can send you my designs. It may also be helpful to have a voice chat in discord, so we can share screens and compare.
Fascinating ... Somewhat off topic, but I am reminded of Randy (The Smurf) who made a dual cannon tee fitting from acrylic and threaded it, etc. so that when it was assembled, he could watch what was going on in side and diagnose problems. It's not something that I would do personally, but I found it very interesting. It makes me wonder if someone could 3D print a cannon with transparent resin, so that the internals would be visible. That would be spiffing cool. (Myself, I think I'll stick with brass & copper, but I'm a stick in the mud like that, you know)
I may have some pictures of that somewhere. It was nicely made. The prototype cannon from strike models that was made out of plexiglass was very cool too : )
I second every one of Kotori’s points. I finally have a good, reliable design for my guns. It took a LOT of trial and error. The difference between even a few degrees of slope means either slow feeding or constant shots. Not resin but I prototyped with clear PLA. That way I could see how each shot affected the line of BBs
@Kotori87 @darkapollo - Of course I will take any free advise you are willing to offer!!!! I’ll send you a PM immediately. Thanks for the slicing advice. I’ll design in several more splits. So a few questions… what do you mean by solvent weld? (Not a mechanical engineer…. ) Are there print settings like fill or etc that I should be starting off with? I keep seeing this magnate in today’s designs, but it wasn’t there when I was building ships before. What does it do? Just hold the next round in place? What do you mean Greg designs layer by layer? Why does room temp matter? What are the temps you are using? Is your printer enclosed? Which one do you have? how much slope are you using for your magazines? Are you using a single plane mag like this design or a coil like Greg’s?
The magnet is to help snap the next round into the chamber instead of waiting for gravity. I did not have magnets on my earlier designs but after adding them, the feed rate became extremely consistent. Print settings, I dunno, I have my Ender3 tuned up for ABS. I don’t get any sags in unsupported areas in the magazine tubes. It is enclosed with a space heater to get the air (and metal) HOT. Like, ouch levels of hot. I just use 5 perimeters (so ramps are self supported) and 20% infill. You will also want to check your magazine length. 50x.177= 9” in total magazine length. 75x.177=13.5” 25x.177=4.5 If I recall correctly, you want a minimum of 10* at the final run to the chamber for gravity fed tubes. My designs are closer to 40* down which keeps around 10 BBs in the feed tube. Mine have not been tested in combat (I really need to send those prototypes out..) but have been the best on bench so far. Solvent welding. You need to print the cannons in ABS and solvent weld them. What that means is using acetone to melt the plastic surface. This seals the print and can glue the pieces together.
I printed a kinda-clear cannon to diagnose issues I was having. That's how I figured out it was consistently jamming in the first bend of the magazine. Very hard to see though even with the clear plastic. Also, my phone's slowmo recording is terrible. I may try printing one in clear resin to get something more transparent. The magnet helps a lot with feeding. In general, the bigger the better, to a point. I have a loaner destroyer cannon that feeds uphill through a bend, using the force of escaping gas and the magnet. Very reliable too, as everyone who has borrowed it can attest. Solvent welding is exactly what it sounds like. You join two pieces of plastic into a single piece by melting them with a solvent (acetone). Brush the stuff on to the parts, squish em together, and let it dry. The joint is often the strongest part. Printing temperatures (nozzle temperature, bed temperature, ambient temperature) have a big effect on your print quality. Nozzle temp is how smooth the plastic flows. Bed temp affects how well the part sticks to the bed. Ambient temperature affects how the printed layers cool, and any stresses from cooling/contracting, drooping, etc. This can potentially pull the parts off the bed, split layers apart, or warp parts into unusable junk. In general, hotter is better for most things but there are exceptions. I'll reply to your PM in more detail once I get home.
Thanks everyone! Starting to unpack everything you wrote. I'm starting by adding a slope and curve to the mags. Where are you guys sourcing the springs, pistons, and magnets? Can anyone share a link?
Beaver makes springs, not sure where anyone else gets theirs. Magnets? Amazon. I use 3x5mm but there is no set size. Pistons. I have been using these. Very easy to chuck into a drill and cut down to shape. https://www.mcmaster.com/51055K78/
darkapollo nailed it. I get springs from Beaver, and magnets from amazon. I usually use 6mmx6mm magnets for 3d-printed cannons, though. For pistons, the plastic parts darkapollo linked work great. I have a benchtop lathe though, so I use the stainless steel rivets from mcmaster that people use in the brass/copper cannons, then turn down the rivet base to the correct diameter for my cannons.
@Beaver - How much are these mythical springs? @Kotori87 @darkapollo These magnets? https://a.co/d/hKw93QU
