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Question about Piston Material

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Question about Piston Material

Unread postAuthor: leachja » Wed Jul 11, 2007 5:22 am

Hello all,
First post here, but I have already built a few cannons.

All the cannons I have built have been sprinkler valve controlled. I am now building a t-shirt cannon that I need to be extremely portable and 100% safe.
I have quite the wood shop, so tools are very easy to come by to construct my own piston valve.

So, my question is this, has anyone used wood as a piston material with any success? I am considering doing it with this because it will be very easy to lathe down to the proper size and be able to throw O-rings on it as well. I am most likely going to use Oak or Jatoba if I can find it in the correct size.

My idea for this cannon is full copper. I have some 3" and 4" copper lying around that I am going to be using as the barrel and the chamber respectively.

I plan to biuld a barrel sealing valve out of a 3" copper tee with a 2.5" port.

So, the question once again is, anyone have any success with wood for piston material. I will most likely use neoprene or a 3" rubber gasket for the sealing face.

Any thoughts would be greatly appreciated.
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Unread postAuthor: MrCrowley » Wed Jul 11, 2007 6:07 am

Wow, copper costs alot as you may or may not know so the tee and fittings will cost a bit. A few people have made wooden pistons with success like member jrrdw:
http://www.spudfiles.com/forums/viewtop ... html#34702
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Unread postAuthor: spud yeti » Wed Jul 11, 2007 8:00 am

Yeah, the tee could be pretty flipping expensive! I would say use something hollow for a piston that size (4") and fill it with foam etc because solid wood would probably weigh a lot! Otherwise hollow the wood out with some fancy tool if you really want wood.
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Unread postAuthor: leachja » Wed Jul 11, 2007 10:55 am

I know it tends to cost more than pvc, but considering that I already have the chamber and barrel material, the T is relatively inexpensive (around $20). The biggest reason I am going to use copper is because it isn't going to be only me using it. It is going to be used at my parents speedway and I'd like the maximum amount of safety for everyone involved.
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Unread postAuthor: mopherman » Wed Jul 11, 2007 10:59 am

leachja wrote:I know it tends to cost more than pvc, but considering that I already have the chamber and barrel material, the T is relatively inexpensive (around $20). The biggest reason I am going to use copper is because it isn't going to be only me using it. It is going to be used at my parents speedway and I'd like the maximum amount of safety for everyone involved.

I would make sure that copper isnt dwv. i heard that dwv copper is bad....
post some pics cuz i would like to see the 4 copper.
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Unread postAuthor: spud yeti » Wed Jul 11, 2007 12:08 pm

Yeah, just check what its rated to, because you could waste $20 otherwise! If you want REAL safety, go all metal using steel etc!
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Unread postAuthor: leachja » Wed Jul 11, 2007 1:54 pm

Thankfully, my father in law is a plumber. The copper is rated around 1500PSI plus, and there is some dwv copper, but it is actually somewhat difficult to come by because it has been mostly phased out since the advent of cheap abs.
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Unread postAuthor: Pete Zaria » Wed Jul 11, 2007 2:05 pm

@leachja,

1) Yes some people have constructed wooden pistons with success, but they are prone to cracking/shattering if subjected to sufficient force. If you go this route, use a very hard, dense wood, and an adequate bumper behind it. I'd recommend finding a better material though.

2) A 2.5" porting piston in a 3" tee is OVERKILL for a T-shirt cannon. Unless you intend to run this at extremely low pressures, you can go down to 2" or even 1.5" porting with very little performance decrease (we're lobbing t-shirts here, not putting golf balls through car doors.... right?)

3) It's kind of a shame to waste 1500-psi rated copper for a T-shirt gun. I'd consider building the t-shirt gun out of cheap PVC and saving that copper for something much more... destructive :)

Just my $0.02.

Peace,
Pete Zaria.
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