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Hello all, my first cannon ever! All aluminum piston valve

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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Hello all, my first cannon ever! All aluminum piston valve

Unread postAuthor: Dirtman » Wed Feb 15, 2012 7:30 pm

Hello Everyone! This is my first post and first cannon ever built.

I only found this site after I was finished building. (really could have used this place during the build) :banghead:

I started building this cannon as a way to launch heavy baits while surf fishing for shark but it quickly got out of hand. As for the specs - Its all aluminum, 2" ID barrel, 4" OD chamber, The piston is made from teflon, 1.5" rear ball valve, So far its only been fired with compressed air at 120psi but I built it to run on helium at 200psi. Everything except the fittings and valves were machined, welded, and built by me (yes I work as a welder).

I had a few problems initially, first I kept blowing out the rubber seal on the front of the piston. I had tried to glue it but ended up tapping the teflon and using a bolt/washer to keep it from flying off. Next I realized its too heavy to hold and fire so I had to make a mount to put it on a tripod.

After that it was mostly minor problems, leaky fittings etc but now it works like a champ. I was able to put a few spuds through some pieces of plywood and launched some at a friends farm. I'm excited to try it out on helium this weekend to see what it can really do.

Anyway here it is! I'd love to here some feedback if anyone sees areas where I could improve my design. And yes I am already planning to build another one! :D
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Unread postAuthor: Goats spudz » Wed Feb 15, 2012 8:11 pm

Is that a relief valve on the side?
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Unread postAuthor: Dirtman » Wed Feb 15, 2012 8:20 pm

Goats spudz wrote:Is that a relief valve on the side?


Yea, since I'm going to be running from high pressure helium tanks I wanted a safety backup in-case a regulator fails. It also makes it easy to drain the pressure without firing if I have to.
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Unread postAuthor: Gun Freak » Wed Feb 15, 2012 8:55 pm

Dude that's freaking awesome! :D

Unbelievable for a first.
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Unread postAuthor: evanmcorleytv » Wed Feb 15, 2012 9:26 pm

Very sexy cannon!! Especially for a first!! Nice job!!
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Unread postAuthor: Moonbogg » Wed Feb 15, 2012 11:07 pm

That is fantabulous! First cannon really? Superb.
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Unread postAuthor: mobile chernobyl » Wed Feb 15, 2012 11:51 pm

VERY NICE! what kind of amperage were you pulling when you did that?


I'm just starting to get more comfortable with aluminum and I'm quickly finding my 160A inverter machine has its limits when it comes to aluminum!
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Unread postAuthor: Dirtman » Thu Feb 16, 2012 12:25 am

mobile chernobyl wrote:VERY NICE! what kind of amperage were you pulling when you did that?


I'm just starting to get more comfortable with aluminum and I'm quickly finding my 160A inverter machine has its limits when it comes to aluminum!


Probably around 220-240 amps for the rear flange and the barrel to chamber adapter (both are very thick), and 180-200 for the barrel gussets, bungs, and tripod mount. Possibly more but I always leave my machines at max and rarely turn around to see what the volts/amps are at when I'm on the pedal. Aluminum does like to suck up heat though, I rarely use less than a 300 amp machine unless I'm working with thin sheet.
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Re: Hello all, my first cannon ever! All aluminum piston val

Unread postAuthor: jackssmirkingrevenge » Thu Feb 16, 2012 1:16 am

Dirtman wrote:I started building this cannon as a way to launch heavy baits while surf fishing for shark but it quickly got out of hand.


Clearly, you could easily just go ahead and harpoon the damn things with this :D

Superb job, needs videos :) looking forward to more.
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Unread postAuthor: pneumaticcannons » Thu Feb 16, 2012 6:26 am

Wow :shock:
thats absolutely amazing... couldn't believe it was a first.

What are those sci-fi looking things connected to the barrel? reinforcements or just decoration lol
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Unread postAuthor: jackssmirkingrevenge » Thu Feb 16, 2012 6:33 am

I'm excited to try it out on helium this weekend to see what it can really do


As helium is significantly less dense than air, you have a good chance of going supersonic ;) find a friend with a chrony
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Unread postAuthor: Gun Freak » Thu Feb 16, 2012 6:48 am

PC they look like barrel supports to divert stress away from the connection.
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Unread postAuthor: Dirtman » Thu Feb 16, 2012 7:20 am

pneumaticcannons wrote:
What are those sci-fi looking things connected to the barrel? reinforcements or just decoration lol


As gun freak said, they add support to the weld on the barrel/chamber connection. The only part I did purely for decoration was the muzzle break.
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Unread postAuthor: sharpshooter11000 » Thu Feb 16, 2012 8:11 am

Truly amazing for a first cannon! Congrats!
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Unread postAuthor: Technician1002 » Thu Feb 16, 2012 10:10 am

The build quality is first class. Well done.

I would like to hear it fire. I suspect the cannon has a wide ratio on the piston. What I mean by that is the piston OD is the chamber ID in size, but the valve seat is the barrel diameter. This will result in a piston that will open while the pilot pressure is still relatively high. This can cause the piston to partially open and then rapidly re-close as the chamber pressure drops faster than the pilot pressure.

A piston with an OD considerably larger than the valve seat diameter will open with the pilot pressure at a relatively high pressure resulting in it opening only partially as the chamber pressure drops. This is the cause of honking of some designs. The large ball valve trigger can compensate for a wide ratio piston.

Image
A smaller diameter piston could be a large improvement on the design. A 3 inch piston cylinder welded on the back flange to hold a 3 inch piston can remove almost 1/2 the piston weight and require the pilot to vent to a much lower pressure before the piston valve cracks open, resulting in the valve popping all the way open and remaining open longer. I used this rear piston cylinder design in my Mouse Musket. I put a 1.5 inch piston in the breech of a 2 inch cylinder and used a 1.25 inch diameter valve seat.
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