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Opening Cannon

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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Opening Cannon

Unread postAuthor: Shrimphead » Mon Apr 14, 2008 11:23 am

I built a co-axial piston gun with a 3" chamber and a 1.5" barrel. This gun is like my avatar. The barrel goes through a modified 3"-1.5" bushing, that fits into a coupler on the chamber. I wanted to test the gun to make sure everything was working before I glued it all together so I wouldn't have to cut it open if there was a problem. So, I put some duct tape around the reducer bushing that connects the barrel to the chamber and shoved it in there nice and hard. Then, when testing the gun, it had problems holding pressure- the air would leak into the barrel. I realized that I hadn't properly sealed my piston and that was the reason for the leak. But now, I can't get the bushing out of the coupler because I had shoved it in too hard. I need to know how to get it out so I can fix my piston. Any ideas? The bushing stayed in under 40 psi- that is about as high as I could fill my gun up to because of the leaking. I have opened up the back of the gun a little and have tried pushing on the piston to push the barrel out, but it isn't working. So does anybody have any suggestions of how to get the bushing out so I don't have to chop my gun and buy more expensive 3" fittings?
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Unread postAuthor: THUNDERLORD » Mon Apr 14, 2008 11:31 am

Try heating it in water, not too hot, just gradually hotter.
Heat usualy works with metal bolts because the outer tube expands more than the inner piece (or bolt).

Other than that try cooling the inner piece.
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Unread postAuthor: Shrimphead » Mon Apr 14, 2008 11:34 am

Umm... It's pvc, not metal. Does pvc really expand enough? Thanks for the help, though.
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Unread postAuthor: sniper hero » Mon Apr 14, 2008 12:43 pm

I had the same problem
I don't know if yours is worse than mine but I took a big leather glove
then put 3 bar on it and then pull
after that my fingers hurt but you can try with less pressure and hard pulling.
:D
or maybe you can get some soap (thin)and try if it goes between the PVC
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Unread postAuthor: jrrdw » Mon Apr 14, 2008 1:30 pm

Use a hair dryer to heat the outside pipe then pull.
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Unread postAuthor: iknowmy3tables » Mon Apr 14, 2008 1:54 pm

you have a coaxile held together by friction :shock:
you can't test a gun unless it can hold presure, pistons operate on presure how could you test it with friction, thats really unsafe

pvc will soften with heat so try that but I don't get whats the problem, you have a gun held togeter by friction? blow it up, use a compresor, just becareful
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Unread postAuthor: Pilgrimman » Mon Apr 14, 2008 4:51 pm

I had exactly the same problem. I just used the clamp mounted on my dad's workbench, and twisted the gun until the bushing slid out.
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Unread postAuthor: Shrimphead » Mon Apr 14, 2008 8:21 pm

@ iknowmy3tables: Actually, it wasn't unsafe, because I was careful to make sure nobody was standing where the bushing could come out and wasn't using high pressure, just enough to test the piston- the whole testing idea worked actually with no problems, no injuries, I just can't get it out because it's too tight.
Did you not understand? I can't pump it up enough because of the leak to pop it off or I would.

Thanks for the help everyone, I'll try these ideas. If anyone has any others I still am very interested in hearing them.
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Unread postAuthor: miskaman » Mon Apr 14, 2008 9:29 pm

I had this same thing happen to me with a 4" x 2" bushing stuck on a piece of 4 inch PVC. It helps to have 2 people to get it off. I just bear hugged the 4 inch as tightly as possible, and then my friend put a clamp on the bushing to get better grip, and pulled while twisting it back and forth.
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Unread postAuthor: bigbob12345 » Mon Apr 14, 2008 9:41 pm

Get two very large pipe clamps and twist them out with all your might
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Unread postAuthor: rp181 » Mon Apr 14, 2008 9:52 pm

i did this too, i put 2 flathead screwdrivers between the seam on opposite edges, and twisted, a little gouging on the cap, but no real harm.
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Unread postAuthor: Shrimphead » Tue Apr 15, 2008 5:41 pm

Thank you Jrrdw! The blow dryer worked extremely well. Props to you and Thunderlord. I didn't think that pvc expanded that much, but apparently it does!
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Unread postAuthor: jrrdw » Tue Apr 15, 2008 6:36 pm

Good, now finish it up, post it up, shoot something up, post that up, lets see, Hehehe, WHAT UP?

Did it take a lot of heat to get it loose?

Your welcome.
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Unread postAuthor: Shrimphead » Tue Apr 15, 2008 6:40 pm

Not a lot. I used the blow dryer for a couple of minutes, then pounded the barrel out from the back. I'm hoping to finish this gun soon, maybe real soon because it's spring break, but the tools I need I have to borrow, so that could easily slow me down.
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