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Peanut Butter Piston Questions

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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Peanut Butter Piston Questions

Unread postAuthor: kablooie » Fri Jan 25, 2008 8:15 pm

I am currently working on a 3" piston cannon, and found out that a skippy peanut butter jar fits quite nicely into 3" pipe, with only about 1/16 of an inch between it and the pipe. The jar is plastic, so I decided to reinforce it with hot glue. My initial plan was to completely fill it, but I only had nine sticks, so I instead just covered the inside with about a quarter inch, with about a half inch on the bottom. What I really want to know is, will this be strong enough? I will have the opportunity to buy more glue tomorrow, so If necessary I could fill it up all the way, although I would have part of it hollow for weight reasons. If I can avoid this though, that would be awesome.

Pics:[/b]
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Attachments
Piston Inside.jpg
Inside of piston,
Piston Sealing Face.jpg
Top of Piston (I have not bought the neoprene yet)
Piston Side.jpg
I will try to fill in the holes when I get more
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Unread postAuthor: Novacastrian » Fri Jan 25, 2008 8:22 pm

It seems to me you could do with a can of expanding foam. Hot glue exhibits a tendency to malform, and under repeated firings could cause your piston to jam. A lot of stress will be placed on this one piece and as such you need to make it as stiff as possible. It looks like a nice effort though and if it is able to be serviced throughout the life of your launcher i would try it with just the hot glue.
Otherwise make the piston resemble a recently departed living organism (a stiff). :lol:
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Unread postAuthor: bigbob12345 » Fri Jan 25, 2008 8:29 pm

I agree with nova get some expanding foam and make the piston shorter it doesnt need to be that long other than that it looks pretty good so far.
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Unread postAuthor: kablooie » Fri Jan 25, 2008 8:29 pm

I believe I do have some expanding foam, Should I fill it with that (I think its "great stuff")? It will be servicable, so I could go either way. Also, what are your thoughts on partitioning off some of my most likely large pilot volume with the stuff?
Edit: I made it this large to cut down on the pilot volume, although if it ends up being too large I will just cut some off.
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Unread postAuthor: Novacastrian » Fri Jan 25, 2008 8:35 pm

I think you should fill it with the foam. As for the pilot volume we have all been privy to the many threads that exert a strong liking for a small pilot volume, as such i would recommend filling in all the dead space that you possibly can, just make sure that you still have enough flow for proper activation of the piston.
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Unread postAuthor: kablooie » Fri Jan 25, 2008 8:36 pm

Okay, thanks guys. Expanding foam it is! Now to figure out a bumper...
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