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My First Pneumatic - Mortar

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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My First Pneumatic - Mortar

Unread postAuthor: saefroch » Wed Apr 28, 2010 9:07 pm

This is the first pneumatic cannon I have built and bothered to post on spudfiles. I built one rather ghetto design with the chamber and firing mechanism on this before as a rifle-style cannon, but that was deconstructed and upgraded to build this for a school-related project to shoot ping-pong balls. It exceeded expectations.

Valve: Tee piston valve- 3/4" piloted by 1/2" ball valve, seals to 1/2" street elbow inside bushing- notes below on valve
Chamber: 3/4" 18" galvanized steel
Barrel: 1-1/2" 24" aluminium

I know the C:B ratio on this is absolutely terrible, but that's not really the focus of this cannon. It's a mortar, not a cannon. In a few days the barrel and attachment to the firing mechanism will be decommissioned in favor of a 3/8" barrel.

Notes on tee piston valve: I constructed a rather creative piston in the hopes that I could create a design that would work on a piston hybrid. Well, it could but I won't be using it. It works because it does in fact seal to the inside of the 3/4" brass nipple it sits inside of while sealed to the barrel. It does NOT work because after firing at about 100+ psi., it slams back into the 3/4"-1/2" adapter with such force so as to lodge itself firmly inside, requiring a lot of force with a pair of pliers to remove it for the next shot. I do know that the piston is sealing to the inside of the nipple because when I add more pressure to the chamber the pressure gauge jumps, then settles back down to a more reasonable increase, as the air forces its way past the neoprene washer. The advantage to this? The pilot volume is absolute. No pressure is lost from the chamber when I pilot the valve.

Because of this, ear protection is strongly recommended when firing. The first few shots left my ears ringing, but I learned my lesson quickly.

Comments and suggestions are welcome, but please none criticizing my C:B ratio.

Image

Image

Image

Damage pics may follow, but are rather hard to acquire.

EDIT: If you have suggestions on cushioning the piston as it moves back, please suggest.

Edit by MrCrowley: Your previous title had the impression that your cannon was the first pneumatic cannon on Spudfiles. Just wanted to remove the confusion. Thanks.

Doh! Sorry.
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Last edited by saefroch on Thu Apr 29, 2010 9:44 am, edited 1 time in total.
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Unread postAuthor: deathbyDWV » Wed Apr 28, 2010 9:22 pm

Looks good. I'm not sure about the piston cushion.

Maybe a regular washer and then a rubber washer on top of that to cushion it some... Since it looks like the the back of the bolt would gave to go through it...
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Unread postAuthor: saefroch » Wed Apr 28, 2010 9:42 pm

I'm a little iffy on whether or not that would do anything... but if I use a hammer to drive them into the adapter they might solve my problem. I'll see if I can get it apart and try that out, thanks. Can't hurt to try.
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Unread postAuthor: deathbyDWV » Wed Apr 28, 2010 11:22 pm

The only problem is whether they will fit past the big theads and not be small enough to fall out the back...
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