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This is my new copper gun (should this piston work?)

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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will this piston work

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This is my new copper gun (should this piston work?)

Unread postAuthor: ckman » Fri Oct 17, 2008 11:54 pm

alright here guys this is my nearly completed tee piston gun. Well I need to know if this piston should work

I will soon solder the rest of it together after I know the piston will work

ok well its a 3/4 tee piston

3/4 about three foot chamber

exhaust valve garden hose attachment

and 1/2 barrel
It should soon have a scope and bolt action and a bi pod with coverings on the gun to cover the piston and chamber oh and the sealing face is whoopy chusion rubber
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Unread postAuthor: FordGtMan » Sat Oct 18, 2008 1:07 am

The really only way is to find out. Looking good so far too. What pressures are you planning on using?

Edit: Hold on, are you filling the gun from the chamber or behind the piston because you will probably need a spring if it is filling from the chamber.
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Unread postAuthor: ALIHISGREAT » Sat Oct 18, 2008 1:41 am

yup you should fill from the pilot side to increase the performance because otherwise you will need a spring.
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Unread postAuthor: ckman » Sat Oct 18, 2008 1:41 am

k thanks ya I am filling it from the chamber and i am planning on going up to 100-150 PSI
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Unread postAuthor: starman » Sat Oct 18, 2008 2:00 am

The best thing to do is just try it and start tweaking it. Chances are it may not work optimally or not at all...not unusual for your first piston. Or it could work great. Don't give up on it. Your design looks reasonably solid from the pictures.
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Unread postAuthor: Gippeto » Sat Oct 18, 2008 11:16 am

Looks promising. :)

You may find that you have too much pilot volume. This won't necessarily stop it from working, but it will work better if you can reduce this somewhat.


Best of luck.
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Unread postAuthor: Sticky_Tape » Sat Oct 18, 2008 11:30 am

Looks good. Did you hear of the d/4 rule? BTW how old are you?
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Unread postAuthor: ckman » Sat Oct 18, 2008 12:04 pm

no I haven't heard of the d/4 rule, what is it? oh and I'm 12
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Unread postAuthor: jrrdw » Sat Oct 18, 2008 12:15 pm

The rule is the piston only has to move 1/4 of the barrel diameter.
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Unread postAuthor: Pilgrimman » Sat Oct 18, 2008 1:25 pm

You only need your piston to move back 1/8" when it opens. It's the distance that allows the highest flow, with the least amount of piston travel. You want to minimize piston travel because it requires the gasses to do work on the piston to push it back, when they could be doing work pushing the projectile forward :D

This seems like a really cool project, btw. Can't wait to see some pics :D
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Unread postAuthor: ckman » Sat Oct 18, 2008 2:42 pm

oh ok thx guys, If i put a spring in how strong does it have to be or how loose
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Unread postAuthor: jrrdw » Sat Oct 18, 2008 5:12 pm

The spring should push the piston to the sealing posision. Just to the point of sealing against the barrel.

What are you going to use for a sealing face and bumper?
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Unread postAuthor: ckman » Mon Oct 20, 2008 11:15 am

Wait what is the bumper is it the part that seals off the barrel? For the face i am going to switch to bike inner tube rubber in stead of whoopee cushion.

Oh and heres another question for You guys the dowel can fit perfectly into the 3/4 piping were it is supposed to seal but I think that will be a problem.

so what should I do and if i increase the dowel size the little blocks in the tee will stop it.
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Unread postAuthor: Gippeto » Mon Oct 20, 2008 11:22 am

Make your piston like this.

Click on the link.

http://www.spudfiles.com/forums/download,id,8951.html


The bumper is the rubber washer behind the piston.








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Unread postAuthor: ckman » Mon Oct 20, 2008 1:03 pm

wait so is the little nipple part supposed to seal the inside of the barrel
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