[3DP] Big Gun cannons!

This is the beginning of an ambitious project: to design a generic Big Gun cannon that can be 3D printed and used in combat. The first objective is to produce a cannon base suitable for a single battleship turret of up to 4x 1/4" barrels, with a minimum of tools necessary for completion asides from the 3D printer. The second objective is to produce a functional rotating two-barrel magazine, again with a minimum of tools asides from a 3D printer. The final objective is to adapt the basic design to a variety of different uses, including other calibers, number of barrels, torpedoes, and different diameter accumulators.
That said, I've already hit my first sumbling block. The local hardware store does not carry good ABS pipe. The only stuff they have is the non-pressure-rated plumbing ABS, and the smallest size they carry is 1.5" ID, way too large a size for all but the largest of battleships. Does anyone know a good source of ABS pipe that *can* be used for pressure vessels? Or should I just set up a carefully controlled sample accumulator and test it?

 

That is my expectation too, but where to I order it from?

 

Will the ABS from Mcmaster work? http://www.mcmaster.com/#abs/=q1trzq I'm very interested in this. If there is anything I can do, let me know.

Beaver

 

Yes, I think it would. The 1.5"OD stuff is probably overkill, but I'm not sure if the 1.25"OD stuff is enough. I guess there's only one way to find out. I'll start drawing up some designs to fit those dimensions and place an order.

 

Do you have anything drawn up yet for the guns? And how do you plan on making it compatible for different loads?

Beaver

 

I'll draw up accumulator designs for both sizes. The nice thing is they both have the same ID, which makes things easier. Then we just tweak the final print diameter to match the pipe when it arrives, pressurize it to 250psi (inside a bucket, inside the pool) and see if it pops.

I think I have a few buna balls, but they are in the car right now it'd be rather difficult to check.

 

Which grade of ABS pipe are you looking at? Class E (which I think is also known as PN15) is rated up to 10 bar at 40C. (although I suppose that the CO2 is always cold -- perhaps PN10 (rated for 10 bar/150psi at 20C, but only 7 bar at 40C) would be OK?

These may be UK/Australian specs, not US...

 

We use PN 15 or better, PN 10 is too thin.

 

Wow, I didn't even know that ABS was available as pressure-rated pipes. We were going to use ABS pipe from McMaster-Carr, because all of the other suppliers we'd found only make non-pressure-rated sewer pipes from an ABS foam.

 

I would love to get in on this. I just purchased a 3DP with my tax return and have been secretly designing my 'Iowa' cannons of 3x1/4's
Maybe us 3DP guys can get together and provide this community a real service by producing the hardest to find parts to our boats?

 

That has always been the largest obstacle. Cannon availability, followed by price.

 

What is the biggest challenge to 3DPing Magazines? If we could get those printed and the actuator portion of the accumulators to were you only have to insert the ball. it would solve the cannon issue wouldn't it? Leave the accumulator itself unprinted so the captains can use the size/shape they prefer.

 

The magizine will be the easy part. Heck you can even make them with some PVC and lexan, no need for it to be printed. The air chamber and loading ramps are the hard part for manual building.
The cannons that I am building are based off of paintball gun mechanics. I do not intend to use a large solenoid and ball valve, instead I am opting for a much smaller eletro-pneumatic solenoid and a poppet style valve. They will be larger than the traditional BGC, but I will be able to run them off of a 9v battery (and a paintball gun board so I can program dwell and timings for the 8sec dely). The Iowa class has plenty of room for a bit larger cannon set up, as I am already mocking them up in my Jersey.

Let me sketch up what I am thinking of really quick to show you.

THIS IS NOT TO SCALE!
The barrel will be articulated so it actually looks proper (IE the whole top doesnt rock back and forth like they do now with the flex point on the mag)
The barrel 'starts' inside the magizine, providing for a longer push to get the ball up to speed, meaning lower pressures are needed. If I gave you only 1' to accelerate a ball up to 100fps you would need much more force than if I gave you 2', thus saving on air. Because of this lower air pressure there is no more need for a directly actuating ball valve. It is replaced by a poppet and pneumatic hammer. Now I know what you are thinking, but if that system is able to get a paintball which weighs considerably more, and is significanly larger than even the largest BB we shoot, up to and well OVER 300FPS with in 6" (shortest barrel I own is a 6") then the airflow provided should be MORE than ample for a tripple 1/4 gun.
The pneumatic hammer system operating on only 70PSI can open that valve with more than 300PSI pushing against it, we use half of that pressure.

The best part is, almost all of it can be purchased at Lowes/Home Depot/ACE, etc.

I am going to be doing some heavy testing of my design when my 3DP arrives.

Here is a scale rendering:

 

SO just looking at your rough draft it looks like there is a potential for jamming because the ball wont push the next round back up the ramp Like here:http://www.rcwarships.com/rcwarships/

If I am seeing your drawing correctly how does the cannon prevent multiple rounds from entering the horizontal barrel? If a ship lists it could feed multiple balls could it not?

 

There is a plunger on the right side of the opening in the drawing. The breach is just large enough for a 1/4" BB enter, there is no way for multiple to roll in. I need a way to keep the ball from rolling back down the barrel at rest. Probably a little dent to keep the ball in place until it is pushed by the plunger.
When the trigger is pulled, the plunger pushes the ball into the breach, preventing the next round from dropping in. I did not draw all of the air passages, or the specifics of the plunger.

 

One of the ideas I have floating around in my head is to 3DP the magazine out of say ABS in layers similar to the what Kotori has done with laser cutting on another thread. Use screws to hold it all together and I think I read that you could use Acetone to help "glue" pieces together.

 

So does it close when fired? or before fired?