One of the biggest obstacles to building a Big Gun warship is obtaining the guns. Standard Big Gun cannons are complex to make, requiring a lathe and a mill, and the skill to use both machine tools. I have made a number of cannons myself from PVC, copper, brass, and other common cannon-making materials. The purpose of this experiment was to see if a Big Gun cannon magazine could be produced via laser cutting, and if such a production method would reduce the tooling and cost required to make a Big Gun cannon: I ordered my magazines from www.customlasercutting.com. I have ordered stuff from them before, and they have good prices and fast service. I drew up a basic two-barrel 7/32" cannon, of 3" outside diameter and single-layer magazine. Here are the plans I drew. In the upper left is the bottom layer, that attaches to the cannon base and holds the set-pins that adjust the balls in the breech. In the upper right is the manifold, that distributes air to the two barrels. Lower left is the ammo ramp/breech level. Lower right is the magazine level, that also holds the barrel risers. I sent in my plans, and within a couple days I got a quote of $39 for two magazines, shipped to my door. That's $20 per magazine! Four days after that, the parts themselves arrived. The laser-cut parts were not all that I required to complete the cannon. I still needed a pair of barrel risers, a rotation bearing of some sort, a magazine lid, a separation layer between the ammo ramps and air manifold, and a cannon base to complete each cannon. I had a pair of cannon bases left over from when I re-armed my destroyer Z-25, that were ideally suited for the project. They had originally been rotating cannons, and were already prepared to accept a rotating magazine. All I had to do was get the right size rotation bearing. For rotation, most cannons use ball bearings. These make for smooth, low-friction rotation, but are expensive and complex to make. I chose to use simple bronze bushings, instead. I specifically chose bushings of 1/2" OD and 3/8" ID, with a 5/8" flange. In order to adapt the magazine to the bushing, I did have to do a tiny bit of cutting with a lathe. I chucked up the magazine's bottom plate, and used a 5/8" end mill bit to cut a flat-bottomed 5/8" hole a couple thousandths past 1/16" deep. This allowed the bushing to sit down in the bottom plate, with the manifold plate sandwiching it in and preventing the cannon from falling apart. Despite being only a bushing and not a proper bearing, rotation is smooth and low-friction. I don't think I will ever use ball bearings again, now that I know simple bushings work just as good. I also threaded the two setscrew holes, and installed the 3/8" long #4-40 setscrews that hold the balls in the breeches. Next, I needed to make a magazine lid and another layer to separate the magazine from the manifold. Without the separation layer, ammunition would drop down into the manifold, and actually fall down into the buna-ball valve itself, which is not good for functionality. The same design could fill both roles, I just needed to make four of them. I chose to use lexan, the same material that I use for blast shields in my battleships. It is thin, strong, and almost as clear as the acrylic the rest of the cannon is made of. To make the pieces, I carefully traced and cut out four 3" circles of lexan with scissors. Once I had the four 3" circles, I placed each one under one of the magazine layers, and used that as a drill bit guide to drill the four screw holes and the two 1/4" holes. I was able to do this step using only an electric screwdriver and a couple drill bits. Here is the finished piece: Barrel risers were 1/4" OD K&S brass tubing, cut to 3/4" length and glued into the magazine layer with clear, rubberized CA glue. I made them with my dremel and cutoff wheel, then deburred them with a drill bit. I held each magazine together with four 1" long #2-56 screws. Assembled, the cannons stand 2.35" tall to the tops of the magazines, which makes them well-suited for small ships like predreadnoughts. The laser-cut magazines themselves are 1" tall. Each magazine holds up to 117 rounds of 7/32" ammo. For my Mikasa, there will be enough room for another layer of ammo and a micro servo for depression. Today, I pressurized the cannons and fired them for the first time. This test was just to see if the acrylic is sturdy enough and the reloading is reliable, so no barrels were attached. I discovered two things: first, the cannons work great. Reloading is reliable, and the laser-cut acrylic parts did not shatter. I also discovered, however, that I need to use T-nuts to hold the magazine together. The thru-holes I had cut for the #2-56 screws were actually a hair small, so the screws actually lightly threaded in. This did not work very well, as repeated firings started to pull the magazine apart. In the future, I will properly size the holes in the bottom layer for tapping to #2-56, but for this pair of magazines I will need T-nuts.
Thanks! The laser-cutting place can also do ABS plastic. I theorize it is possible to laser-cut cannon bases, as well, but it would be a lot trickier and more risky, since the parts would be under pressure continually rather than only while firing. Maybe for my second predreadnought, since these ones are going in my first...
You will find that the oscillating pressure is actually the worse than the steady pressure case if they are the same pressure and you are anywhere near not being horrifically over designed for the static case. beyond that, with dissimilar pressures, (steady versus oscillating) the analysis gets quite detailed to account for both the steady load and the fatigue cycle.
Absolutely fabulous! Very well done! Also, that you for posting up plans too! However, I am surprised that the cannons feed reliably... Do they continue to feed well even when they run low on ammo? It seems like they would need to have some rounds in the main magazine to force rounds down. Please keep us posted!
Nicely done! A couple of questions, however, Do your feed ramps have any slope to them (i.e. are they ramps?) If so, how did you impart the slopa? If not, in testing, when the magazine is starting to run low (to, say not quite full feed slots), it would appear that the ship would have to be listing away from the muzzles for the next round to load. Also, it would sem that, if not a ramp, that the geometry of a flat slot would be more susceptible to "machine-gunning" or "spurt fire" if the gas is applied too long - did you notice any double firing? I know Pololu has some issues with 6mm or larger being laser cut - I am assuming you went with 7/32" as it is within the 6mm envelope? Pololu could also cut (etch?) somewhat (did so for the O-ring glands in my prototype liding breech gun). If Customlasercutting.com can do the same, y9ou might be able to get your rotation bearing lip "etched" to save the machining step. ABS may be stronger/more durable, but your guns in acrylic would be great for shows like Maker Fairre to show the inner workings. Cheers.
That's why I chose Acrylic. There are two or three new members who didn't know how our cannons worked. I showed them this, and it was a very helpful visual aid when describing how cannons work. These cannons will also be making an appearance at Wooden Boats on Parade in San Francisco this month, and a few other shows this year. On the whole feed ramps thing, I actually ran an experiment. The first cannon simply has flat ramps. No slope whatsoever, but with a 1/8"dia 1/4" long rare earth magnet between the two setscrews in the breech to encourage reliable loading. The other has the same basic setup, but I angled the ramps by applying some silicone glue and squishing in a 1/4"dia rod, then trimming away the excess when it dried. Tests so far show that both load very reliably, and neither one has demonstrated a machine-gun tendency yet, but my tests were not very extensive. Once I install T-nuts to properly hold the cannons together, I will perform more extensive testing, to find out about gas consumption, long-term durability, etc. I think, for the next round of cannons, I will try building the magazines up from many layers of 1.5mm material, rather than fewer layers of 6mm material. That will allow me to cut the bushing lip without a lathe, cut the separation layers instead of hand-making them, and even cut a sloped ramp by stepping the layers.
This is pretty awesome, my brother and I have been working on different designs, and our first proof of concept was slowing down the air too much. (we were getting very little penetration at 120 psi) We'll definitely be giving these guys a call.
After reading your post here, I drew up a set of plans for the paddlewheels I will need, and had them give me a quote. $38 is not bad, they emailed me today and said they shipped, again not bad in 2 days. I contacted a company in England and they wanted over $300 for about the same thing.
I'm betting ACW. Gotta be ACW. I'm betting one of those paddle wheel gunboats. Make sure you post pictures
No it will be IX-64, Wolverine. I have a set of builders plans that are not bad, just need to blow them up around 33% or so. 29 inches long, need to be 39+. Rudder on the bow and stern, so they can be 50% larger, will still turn slowly, but its a convoy ship. Just point it at the harbor and motor across. With the large overhang side mount hits will be hard to do, so they will need to stern it to death, but with the Axis going all sidemounts as they are, it may actually make a trip or two. But it will be fun to run, and somthing different. My Fa de Bruno this year at Nats went back and forth twice, at speed 46 sec, any faster and it submerged, and was only hit twice total, the rest just deflected off the sloped top deck, and was fun to run to boot. The smurf man tried and tried to hit it to no avail.
You've got a ship with a pair of beautiful side paddle wheels, and you're wondering about RUDDERS!? Dude, it's all about differential steering! Actually, more to the point, those rudders are going to struggle to turn the boat without prop-wash going over them. I'd also make sure the paddle wheels are bullet proof. What did you think of that slow speed for the Faa di Bruno? 45 seconds is 25 knots by the Big Gun speed chart, which is the minimum speed.
Actually, he can't do differential steering, which is why he was lamenting the slow turn. Differential steering is illegal under the current rules, and if the paddlewheeler gets to use it, then every other warship would have a valid arguement for using differential steering, too, because all real warships do it to improve handling. If it came to a local or regional, I'd vote to let it run with a chit, because it would look awesome, and it's not like it's 8 units, and I'd like to see it running around the islands on the lake in Pooler. Be really hard to score on it in that environment with the differential steering, and with strong enough motors on the paddlewheels, it'd be pretty resistant to mossing (I hope!).
Clark is right, it MWC no differential motor control. Besides the real thing had a single engine, and the paddles were ganged together. She will be a very slow turner, but interesting none the less.
The Fa could go 34 second speed, but the model could not go much over 45. Infact I slowed it down to 48 if I remember right. But it did run 34 in reverse. If anyone got close, I just hit reverse, threw the rudders over, and it stood up on its stern, pivoted around in about 6 inches, and off I went the oppisite direction, very hard to hit. At one point I started playing around with Foster's Andrea Doria. I place the stern against his side, and hit full reverse, I almost sank his ship, and had to stop. He did say it was ok to give it a try.
Hi I did find this thread most interesting, while it was about lasercutting guns for big gun.. /Markus
Kotori I got the paddlewheel parts in today, very nice workmanship, they go together perfectly, now to just build the boat.
