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Best Plastic to use for piston?

Post about things you have launched or thought about launching. Also post about various materials used for building cannons. No posts about explosive projectiles!
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Best Plastic to use for piston?

Unread postAuthor: SubsonicSpud » Mon Feb 09, 2009 6:06 pm

G'day guys.

I am about to machine a 20mm barrel seal piston for a mini cannon, and I am just looking for suggestions for the best plastic to use for it. I am stuck between a choice of Nylon, Acetal, PTFE!

Any suggestions on the best one to use?

Cheers
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Unread postAuthor: daberno123 » Mon Feb 09, 2009 8:11 pm

I don't really have any experience with any of them. But I hear Delrin (Acetal) is quite easy to machine.

hoarp001 used it in his monster tennis ball gun

Click on the links at the bottom to see the pictures of the piston being machined.
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Unread postAuthor: jonnyboy » Mon Feb 09, 2009 8:17 pm

I have no experience in any of those materials but I've heard of people using nylon in high pressure guns.
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Unread postAuthor: SubsonicSpud » Mon Feb 09, 2009 8:56 pm

I am tending to lean towards Nylon because i think it is less brittle than acetal, but i dont think it machines that well.
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Unread postAuthor: Gippeto » Mon Feb 09, 2009 9:49 pm

I used nylon pistons with great success in both my copper gun and my "bb" gun.(Both run at 400psi.)

The bb gun uses a teflon sealing face, which is set into the nylon piston, and (now) secured with a small screw.

Great stuff for pistons IMHO. :)
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Unread postAuthor: Biopyro » Tue Feb 10, 2009 2:14 pm

I am currently in the same situation, and from my research so far I think I'm going to go for nylon 6 (not 66). It is lighter (~1.1g/cm) than acetal (1.6g/cm), and has slightly better impact resistance. It's easy to get it pre-lubricated with mos2 (making it black), and is much cheaper than PTFE.
I know acetal is very easy to machine, but I don't think nylon is hard as such.
Edit: Just looking at HDPE rod - it is about 1/3 cheaper, and has a lower coefficient of friction - good if you're not using O-rings. Nothing on it's impact resistance though.
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Unread postAuthor: SubsonicSpud » Tue Feb 10, 2009 2:58 pm

Well i have ended up buying Acetal for the piston, the guy from the place I bought it from suggested it over Nylon due to its machinability. I made the piston last night an am verry happy with the results, definatly machined a lot better than any other plastic i have tried.

Cheers
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