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My First Piston Experimenting with Pics and Damage

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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My First Piston Experimenting with Pics and Damage

Unread postAuthor: Braddubya » Wed Jan 07, 2009 12:33 am

I was looking at some scrap PVC and parts I had laying around and decided I would build a mini piston gun so I could at least get my feet wet with pistons. I had some 2" PVC and a 2" hole saw. So I cut 4 plugs out of a 2x4 and used them as the pilot back, piston, barrel support, and front endcap. Its a co-axile design.

Figured I would start with this pic just so everyone knows I learned my lesson
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The Main Parts

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Barrel support and endcap assembled

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The whole system laid out as in final assembly next to PVC

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I eventually replaced the air gun with a ball valve

The piston with my first attempt at finding some bubber laying around my house

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This didnt seal well enough so I had to disassemble it and try again but I eventually found a neoprene patch for fishing waders (spelling?) which once I removed one of the fabric outer layers worked perfectly.

Final assembly

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And just so none of you have to ask. Yes that is hotglue sealing the endcaps. Thats why I added the screws to ensure they will not come flying out. This is just a low pressure gun I made quickly so that I could fiddle with a piston and the great thing about hotglue is that it dries in seconds and once you get it hot again melts so that you can fix the mistake you made earlier :roll:

I have now added 8 screws to each cap just to be extra careful and so far no detectable leaks until I hit 80 psi. Not bad for hot glue :lol: Ill fix this later

And here is my result

At only 30 psi

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Looks like a need to find a new ammo source

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The only problem I have encountered so far is that it fires perfectly at 30-40 psi but at 80 psi alot of air comes out the ball valve before the piston pops. Its still more powerful but it seems like way too much air is flowing out the ball. Any ideas?
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Last edited by Braddubya on Wed Jan 07, 2009 12:46 am, edited 1 time in total.
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 07, 2009 12:37 am

*very* good for a first effort, kudos :) and good for thinking out of the box and not sticking to standard fittings :D

The only problem I have encountered so far is that it fires perfectly at 30-40 psi but at 80 psi alot of air comes out the ball valve before the piston pops. Its still more powerful but it seems like way too much air is flowing out the ball. Any ideas?


You need a lighter, tighter fitting piston and less pilot volume.
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Unread postAuthor: Gippeto » Wed Jan 07, 2009 12:38 am

Your piston is fitting too loose. Give it a wrap or two of good ol'e duct tape to get the clearances in line.

It won't last too long, but it should solve your problem.


Edit: And once more,...beaten to the punch. :wink:
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Unread postAuthor: Velocity » Wed Jan 07, 2009 12:42 am

Bumping the screw count to eight on each plug is a good idea; the wood will not do too much in terms of blocking the pressure, but the wood with a bunch of screws certainly will do a better job.
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Unread postAuthor: inonickname » Wed Jan 07, 2009 12:56 am

+1 to velocity. Extremely good display for a first time though :P I like it.

Just increase the screws in the endcap. I realise you probably want to have access but once you have it sorted epoxy the endcaps imo :P

good luck
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Unread postAuthor: jackssmirkingrevenge » Wed Jan 07, 2009 1:32 am

Consider making a wooden piston about 1/4" smaller in diameter than the interior of the chamber, putting it in a section of chamber tubing and filling the gap with hot glue.
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Unread postAuthor: Braddubya » Wed Jan 07, 2009 5:38 pm

Thanks all for the comments and advice! If I decide to pull it apart I will definitely drill out the piston to reduce weight and make it fit tighter. For now though it is working pretty well :twisted:

UPDATE:

I tried it again at 100psi with some very interesting results!

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Piston Valve - 1
1" Plywood - 0

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Unread postAuthor: CasinoVanart » Wed Jan 07, 2009 5:45 pm

Nice work, fun is it not!! You should see if you can pierce a coin ;)
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Unread postAuthor: Braddubya » Wed Jan 07, 2009 5:53 pm

it was also at a distance of about 20' :D

I may pull it apart get the piston to actuate better and the bump the psi up to 150ish and see how a coin handles it.

EDIT:

Ask and you shall recieve

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Unread postAuthor: sputnick » Wed Jan 07, 2009 6:14 pm

Nick likey!

That is very nice looking I must say, it is so unbelievably simple and clean looking.

A question for those more knowledgeable about piston guns... See the barrel support? Would there be significant increase in flow if there was less material, say just 4 sticks of hot glue? And would the increase be noticeable in the power and piston actuation?
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Unread postAuthor: CasinoVanart » Wed Jan 07, 2009 6:18 pm

Hehehehe, cool as man. Now get another coin and line it up behind the first :D
Have you done any velocity calcs with ggdt?
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Unread postAuthor: maggotman » Wed Jan 07, 2009 6:28 pm

whats stopping the air leaking threw the wood ?
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Unread postAuthor: Braddubya » Wed Jan 07, 2009 6:37 pm

Try number two

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It actually passed right through the penny and knocked the plastic fletching off before embedding itself atleast half an inch into a 2x4 but I put it back together for the picture
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Unread postAuthor: CasinoVanart » Wed Jan 07, 2009 6:48 pm

Throat shot!! Poor Abe...

ANd as JSR would say "it goes to show the power of cross sectional density" or something like that :D
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Unread postAuthor: Braddubya » Wed Jan 07, 2009 7:02 pm

Yea im quite happy with its performance thus far. Could still use some tweaking though

I have not yet tried ggdt Casino. Is pretty straight forward?
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