laser-cut Big Gun cannons

I should have linked to OpenSCAD: http://www.openscad.org/ ! Scroll down to the downloads section.

I don't have a lot of time at the moment, so in the short term development will be slow, but I would certainly like to understand the cannon base and valve requirements/designs better. I'm still intrigues by your mention of the possibility of laser-cut bases, as that makes customisation so easy, but a base that would suit a range of magazines would be good too.

I will get a static set of Clippard bits and pieces before I actually get a ship, but that's months away rather than weeks.

Tom

 

Here's an exploded view of the cannon components: https://skitch.com/tgdavies/846rk/openscad-exploded.scad

I was wondering whether I could remove the setscrews and just make the holes in the manifold cover smaller than the calibre of the ammunition? Would that support the round in the right place?

 

Looks good! in answer to your question, yes you theoretically can simply make the manifold cover holes smaller, so that the rounds set at the correct level without a setscrew. That would even offer airflow improvements. However, it also requires a lot of precision, and doesn't offer any of the adjustability that a setscrew does. So if your initial calculations, or the manufacturer's settings, are off a little, it won't work right and you won't get a good bang. It has trade-offs, but the payoff is good if you put in the effort.
A few other things to consider: laser-cutters are happier when you use a single thickness of material. That means they don't have to change materials half-way through the job. This also means you can use a stair-step approach to sloping the ammo feed ramps, so that rounds will roll down naturally. I didn't do this in mine, and I regretted it.
Another thing: the rotation bearing. I am happy with my rotation bushings, but I also custom machined those on a lathe to get them working right. I'm not sure which approach you were planning, but you may consider using the age old standard rotation bearings.
Alas I have been having trouble with my 3d CAD software. It has croaked on me every time for the past year, on every computer I've tried. Clearly it's Allied sabotage because they're afraid of what evil invention I'd come up with next...

 

Thanks for the comments. I think that tuning the manifold cover hole size would be OK, as you'd just need to make a new cover, no other components.

So perhaps use 2mm sheet and make each layer a sandwich of three parts? (usually identical, but not in case of the ramps)

How does the ball race part of a standard bearing seal? I'm not actually familiar with them. I think using a ball race would be a good idea -- anything which reduces the precision needed is good (yes, I know that's the opposite of my set screw elimination argument )

I was looking at http://www.ntxbg.org/pgOnTheWays/SCBG_Tech/articles/articles_12.html -- is that a good base design?

What exactly is the reason for needing to use a high pressure actuator/low pressure buna ball valve arrangement anyway? Is there simply no standard electrically/manually operated valve which has a high enough flow rate/fast enough opening speed/low enough force required? (I realise the high pressure side is also useful from a safety perspective as a way to vent the accumulators when the gas system is turned off.)

 

The whole dual-pressure system serves a twofold purpose: first, it gives a snappier firing response when you pull the trigger. Second, if you ****ed up your design and somehow ended up with a larger valve than your actuator, it will still fire. But both of those benefits are merely sideshows to the real reason: having separate regulators for each cannon allows you to adjust each cannon independently, which is important when you have more than one cannon.

Personally, I've always designed my ships to operate with only two cannons, to minimize the number of regulators required. Some people don't use secondary regulators at all, and simply build their cannons as identical as possible. I've done this as well. Some people insist on having a separate regulator for each cannon, others (like me) believe it is only an upgrade, not a necessity.

The design you linked to is certainly functional. I don't like how they chose an asymmetrical rotation bearing layer, since that always makes it more difficult to produce and quality-check. But other than that, they take an interesting approach to getting the closing action on the valve. Not the method I'm used to, so I have no idea how easy or hard it is to produce. It isn't something that can be ordered from a machine shop, though, so that may be a minus. Man I wish I could get my CAD software running so I could access my old designs.

 

Is tuning via adjusting accumulator size equivalent to tuning via regulator adjustment (in result, not in difficulty -- obviously the latter is just the twist of a knob). For example, if you had a KGV with quad turrets and a double turret, could you hope to run on a single regulator by picking the right accumulator sizes?

What are the other closing methods?

When you use a ball race bearing, how do you avoid the gas just blowing out between the inner and outer ring?

Apologies for the constant questions -- I have a lot to learn!

 

Tom,

I'll have to download OpenSCAD so I can see what you've put together. Sounds intriguing. Thanks for sharing!

As for the ball race bearing, see this post here on Brian's Blog over at the MABG website. Look for the part about bearing blow-out.

http://mabg.org/node/401
Brian's Blog has a ton of excellent posts about building cannons. Read thru it all. I've read and re-read them several times and I'm still learning new stuff from there.

 

Thanks for the link, that is interesting.

Please bear in mind that I have never made a cannon, nor even installed and tuned one, so my designs are speculative!

 

I haven't made one yet, either, Tom. I'm still doing my research, which is why I'm reading everything I can find on the subject (which ain't much).

 

Good ideas there. I'm very new to this hobby and I've been working on a method where I can use flat stock material (HDPE for example) and nothing more fancy than a drill press. It turns out that hole saws come in many sizes, anywhere from 3/4" dia to womping 6"+ sizes. I was looking at the 3" and 3-1/2" sizes or there about. It also turns out that you can take off the center drill that is there to make sure your circular cutters dont wander. And when one removes a certain spacer, two of those cutting circles fit on the same shaft. Sounds amazingly dangerous and looks mean, but when set in a drill-press, the inner core will bite deeper than the other core, so extra material is needed. Serious clamping (naturally) is also a must. That started me thinking...

So I drew up some plans with the similar/same washer idea shown above, although mine involved a bit more drilling, specifically for the slopes of the ramps. But the trick there (I think) is, to start out with rough, rectangular material to make clamping easier, and includes adding sacrificial stock to avoid the normal drillbits to "wallk" as one drills the slopes. The various wafers could be stacked to drill the smaller holes for the scews to ensure they fit together (laser on the drillpress is a must have). then drilling the larger holes for the barrels and some cutting on a scrollsaw should do the rest.

As far as the accumulator, the popet valve and the bearing goes - those are all clippard parts. They make a nice Rotating Manifold. I drew up all the parts in CAD in 3D and asside from buying a drillpress and the HDPE stock, everything is pretty much set...right, the clippard catalog just came in the other day, so that makes my life easier as well. The layers on the thing would be: Lexan Cover, Magazine (donut) Ring, Feeding Slides, Ammo Breach, Manifold (the hexagonal clippard manifold sits in the center of it) and a base of sorts should do it. (No idea how to post images here...) I'll put up some updates when I start on this project...just about ready to get that rolling. (Need a few capital purchase orders to clear with the boss...)

Cheers,

Thomas

 

I'd be interested in seeing your designs -- can you put them somewhere public -- dropbox or bitbucket.org or similar?

 

Here is a screen shot of the latest tweaking of my HDPE wafer design for the H-39. I have the wafers all drawn up in 2D and 3D with pilot hole locations marked and printed etc. Idea is to stack a bunch of the various thicknesses of HDPE material together, silicone the edges (I'm thinking a 4"wide x 16"long stack of stock material) and clamp it into a vice for the drillpress. That way each "set" of disks will stack and bolt together nicely.
Pre drill all common holes, take it appart, then drill the 20 degree angle slide and the barrel holes, and stack them again, put pins through some of the common holes and use the circular blades to cut them out completely. Sand them, polish them, stack them and use a bit of silicone, add the washer or magnet, test it, cut out the slot for the rotating manifold (probably core it out and then use the scrollsaw for the hexagonal shape of the manifold), and perhaps drill some holes through the sides to screw long screws into the un-used manififold holes for holding the magazine to it, screw it all together, hook up the pneumatics and give it a shot...well, thats all a bit in the future. But with this design, virtually any size cannon can be built, and barrel sizes easily replaced with smaller or larger barrels by changing out the Lexan Cover and the Slide/Barrel Wafer. I'm thinking of using an aluminum bottom as well...I'm sure tons of tweaking might be required. But it might be a start in a direction where the most expense is on good, solid Clippard parts, and the Cannon itself becomes a cutting exercise using scrap material without having to lathe anything.
The Letter & numbers are the codes for the "Blocks" I use to differentiate the disks.

Thomas

 

You've got some great stuff there. A few comments:

1) An MJV valve does not have sufficient airflow to effectively fire more than one barrel. Two bb-caliber barrels may be fired using a Jumbo Quick Exhaust Valve, with enough accumulator and barrel length, but beyond that you will have to fabricate your own valves.

2) excellent idea to pre-drill common holes and use them for alignment. Not many people know about that trick.

3) can you post more information on your design for the rotation bearing? It is very different from most designs I've seen, and I don't quite understand how it works.

 

What about using the MME-32/33/34 series of solenoid valves, which have 49 to 170 cfm at 100psi, vs. the 58 cfm of the J series?

It's hard to see from just an elevation, but does this design reduce pressure loss into the magazine, by having long, narrow feed ramps? Would that allow a smaller valve?

Tom

 

Thanks for the thoughts and advice: the rotary manifold is a clippard part. I have it turned to feed 2 channels. There are 6 small ports. the others I will plug, or should be plugged if I get a tight fit. It can be rotated (with a different manifold channels cut for 3 barrels I immagine - quite easily actually). The lexan (I thought) would be sufficient if I silicone it down and hold it with small washers - or also upgrade it a bit to a slightly thicker material. But I think that it be easy enough to drill 6 holes, or how ever many. I could use steel for the base, but figured aluminum be easier to cut.
I'll have to do some more research on the barrels to use. Seems the 1/4" Stainless Steel Barrels from K&S seem to fit a BB pretty well?
I was thinking about barrel wear...that will happen at the bend. Does it not make sense to make the bend it own part, and use two flexible joints, one to the magazine and one to the actual gun barrel? The benefit of that ought to be, that one can replace the elbow pretty easily, and in addition, have someone who does have a lathe turn the barrel to be more tapered, and add concentric brass tubes for the thicker areas of the barrel. Then use heatshrink and paint it. Rubber should take paint better than steel. For various German vessels, that can be left black...hmm.

Here is a scan of some sheets I have laying around: they are 1 edition earlier, but they show the general gist. None of the sizes are proper yet: still in the "rough" layout stage...

 

I actually know little about what flow rates are required for proper firing, only what I've discovered from testing. A single MJV valve works fine for any single Big Gun shot, given a reasonable barrel length. A high-flow QEV valve works OK for a twin bb cannon with long barrels, but not for larger calibers. Anything other than that should follow the cross-section rule of thumb: you want to have the same total cross-sectional area throughout the cannon. ie you want the cross-sectional area of your three barrels (combined) to equal the cross-sectional area of the valve, and all areas in between.

For barrels, wear only becomes an issue if you use softer steel (like brake line) or thin-wall stainless. Thin-wall stainless you want to avoid anyway because it dents easily and then jams. Brake line, on the other hand, lasts a couple years before failing, and is cheap to buy and easy to bend. I've seen people wear out their brake line barrels, and it took two years of extreme abuse. Replacing those barrels took a couple of hours one afternoon. So there isn't much need to have separate bend and barrel parts. I do know one person who tried it, using stainless steel bends and tight tolerance brass barrels heat-shrunk in place. It looked amazing, but the brass he used would dent and jam at the lightest hit. Fortunately it would only take a couple minutes to replace, but he got sick of replacing two or more barrels every sortie and switched to regular stainless one-piece barrels.

 

> I would urge caution on the 1/8" lexan cap...

Isn't that part pretty much identical to Carl/Kotori87's design in the first post of this thread? Which seems to work?

 

Indeed...its easy enough to double the number to 8 screws. Heck, I could put one every inch around the perimeter. Also, thought about an 1/8" aluminum ring, the same size as the magazine walls, that would sit on top of the lexan, and hold that down with 6-8 screws. That should do the trick. 3/16 or even a 1/4" lexan instead of 1/8" and that should be good, I'm thinking. Looking at the statistics..if even a 1/4" washer is holding down each point, that gives it enough bite.
http://www.usplastic.com/catalog/fi...0Sabic.pdf