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Cast Pistons with o'ring grooves

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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Cast Pistons with o'ring grooves

Unread postAuthor: Novacastrian » Sat Oct 27, 2007 11:15 pm

After trying to figure out a way to make a piston with grooves without the need for machining i came up with the following idea.

What you will need- 1. A short piece of pvc pipe (size of piston).
2. Two o'rings that fits snugly inside said pipe.
3. Two slightly larger or fatter o'rings (for actual use)
4. Cooking spray or similar (so the piston comes out)
5. Liquid gold (epoxy) or plain old hot glue.

How to: Roll the two smaller o'rings down the pipe (this is where your grooves will be), spray with cooking spray or some such then pour in your epoxy or fill with your hot glue.
After this has set remove from the mould and also remove the o'rings from the piston. Get your larger or slighly fatter o'rings and install on your piston.
Hey presto, a high tolerance o'ringed piston without the need of a lathe. :D

Last but not least, drill a small equalisation hole and you are done.

Edit: i will use this method tomorrow and post pics of the result.
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Unread postAuthor: Marco321 » Sat Oct 27, 2007 11:23 pm

Nice work, I'm so gonna do this for my copper gun :D
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Unread postAuthor: spudgunnerwryyyyy » Sat Oct 27, 2007 11:46 pm

Great idea NewCastle man, mabye we could incorporate one of jsr's idea and put some foam in the center to lighten it up. Like marco im going to do this as my piston valve has failed exponentially and i need a very strong and good sealing piston.
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Unread postAuthor: Novacastrian » Sat Oct 27, 2007 11:47 pm

spudgunnerwryyyyy wrote:Great idea NewCastle man, mabye we could incorporate one of jsr's idea and put some foam in the center to lighten it up. Like marco im going to do this as my piston valve has failed exponentially and i need a very strong and good sealing piston.


I would love JSR's input as to the best way to do this with Epoxy.
Thanx gunner :)
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Unread postAuthor: hi » Sat Oct 27, 2007 11:51 pm

you know that really is a great idea, but the problem is that an epoxy or hot glue piston is made so well that O rings are not required. the reason pistons have O rings is so that they are airtight, but if you mold it then it is airtight...
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Last edited by hi on Sat Oct 27, 2007 11:51 pm, edited 1 time in total.
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Unread postAuthor: spudgunnerwryyyyy » Sat Oct 27, 2007 11:51 pm

Well one thing is epoxy doesn't hold tightly configured shapes too great. The corners of the created grooves may get cracked under the intense loads of a piston valve actuating. PM jsr
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Unread postAuthor: Novacastrian » Sun Oct 28, 2007 12:09 am

Hi: A piston moulded as you mentioned will not be airtight. It will be DAMN close to being airtight.
Maybe one could use a slightly smaller size mould. This at the moment is just a theory as i have not made one yet :)

Gunnery: Yes i have thought of that, maybe this design could be limited to small guns? JSR will see this in due time :wink:

Edit: May be there are harder substances that could be used: JB Weld or similar.
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Last edited by Novacastrian on Sun Oct 28, 2007 12:11 am, edited 1 time in total.
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Unread postAuthor: spudgunnerwryyyyy » Sun Oct 28, 2007 12:11 am

Yeah, great to use in small guns where o-rings make the biggest difference and where o-ring grooves are the hardest to machine.
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Re: Cast Pistons with o'ring grooves

Unread postAuthor: jackssmirkingrevenge » Sun Oct 28, 2007 3:38 am

Novacastrian wrote:without the need for machining


This is I believe one of the shining virtues of epoxy casting, in that unlike a machined component, you need only basic hand tools to get a durable and precise result.

Your method sounds like it would work, however I would suggest a slight modification to the design that would reduce drag and remove the need for an equilisation hole.

It would basically function in the same way as the piston head in a bicycle or foot pump.
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Unread postAuthor: Marco321 » Sun Oct 28, 2007 4:24 am

Is there a way to do this but with epoxy putty?
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Re: Cast Pistons with o'ring grooves

Unread postAuthor: Novacastrian » Sun Oct 28, 2007 4:27 am

jackssmirkingrevenge wrote:
Novacastrian wrote:without the need for machining


This is I believe one of the shining virtues of epoxy casting, in that unlike a machined component, you need only basic hand tools to get a durable and precise result.

Your method sounds like it would work, however I would suggest a slight modification to the design that would reduce drag and remove the need for an equilisation hole.

It would basically function in the same way as the piston head in a bicycle or foot pump.


Thankyou for you input JSR I truly appriciate it. :wink:
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Unread postAuthor: jackssmirkingrevenge » Sun Oct 28, 2007 4:30 am

the problem is that epoxy putty doesn't flow so the idea of "casting" isn't really practical, unless you place small amounts into the mould and tamp them down with a suitably sized rod, but in that case don't use o-rings.

Another way to make epoxy pistons with a perfect seal is to use a syringe as your piston tube and use the syringe seal itself to substitucte both o-rings and sealing face, as suggested here

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Unread postAuthor: Marco321 » Sun Oct 28, 2007 4:36 am

Yeah, i previously used the putty to make pistons, it was good, no mess lol. What you could do, is get a washer, and put the o-ring around the washer, then have putty above and below the washer and the 2 layers will bond in the middle of the washer, or a screw all the way through could be used.
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