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hot glue piston q's

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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Unread postAuthor: deusXmachina » Tue Apr 10, 2007 2:50 pm

Ick...I don't like the idea of that it would probably make the sides gnarly and not make it that much lighter. I'd just cut out hot glue where it isnt necessary.
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"On a scale from 1-10, I hope you fall in front of a bus."

:white stuff pours out of piston: "What is that? It looks like milk."
"....<i>Well...</i> it's not milk."

YAAAAAAAAYYYY WE'RE DOOMED!
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Unread postAuthor: rad14701 » Tue Apr 10, 2007 5:25 pm

The whole idea of making the piston fit too snug in the chamber, whether by using O-rings or not, is not going to improve performance... The piston seal does the sealing... The pressure difference causes piloting to take place... Any added friction caused by making the piston fit to snug will only reduce performance... Performance will be optimal only if the piston can move with a theoretical zero resistance... A piston with minimal tolerance and weight will achieve the most optimal performance, even with no equalization port... It's even been proven that something as simple as a rubber ball makes an almost ideal piston for a coaxial gun and a rubber ball has near theoretical zero resistance in comparison to its size...
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Unread postAuthor: AmYisroelChai » Fri Apr 13, 2007 8:34 am

rad 14701 says:
The whole idea of making the piston fit too snug in the chamber, whether by using O-rings or not, is not going to improve performance... The piston seal does the sealing... The pressure difference causes piloting to take place... Any added friction caused by making the piston fit to snug will only reduce performance... Performance will be optimal only if the piston can move with a theoretical zero resistance... A piston with minimal tolerance and weight will achieve the most optimal performance, even with no equalization port... It's even been proven that something as simple as a rubber ball makes an almost ideal piston for a coaxial gun and a rubber ball has near theoretical zero resistance in comparison to its size...


Thats some very logical but contradictaory information to what is beleived on this site. Can you back up that information? How much experience do you have? Have you charted the difference?

I and others are always looking to further our knowledge. But no one wants to waste their money on someones unoroven theories.

I am curious.
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Unread postAuthor: AmYisroelChai » Fri Apr 13, 2007 8:37 am

Ick...I don't like the idea of that it would probably make the sides gnarly and not make it that much lighter. I'd just cut out hot glue where it isnt necessary.


No really because if he added the glue to a 2" molding nothing would be gnarly you would just save money on glue. I thought of this yesterday but have not tested it yet. I was thinking to ise it with silicone. Shave out the insie of a 3" tee so the silicone psiton would be a few mm bigger and then squish it into a regular 3" tee for a perfectly fitting piston.
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Unread postAuthor: Scope » Fri Apr 13, 2007 2:08 pm

rad14701 wrote:The whole idea of making the piston fit too snug in the chamber, whether by using O-rings or not, is not going to improve performance... The piston seal does the sealing... The pressure difference causes piloting to take place... Any added friction caused by making the piston fit to snug will only reduce performance... Performance will be optimal only if the piston can move with a theoretical zero resistance... A piston with minimal tolerance and weight will achieve the most optimal performance, even with no equalization port... It's even been proven that something as simple as a rubber ball makes an almost ideal piston for a coaxial gun and a rubber ball has near theoretical zero resistance in comparison to its size...


You forgot one major thing though... The less tight the seal of the piston on the walls the more air is going to be required to push it back and close the pilot.. This will lead to preformance loss..

Just use pipe as a mold, add a sealing face, lube it up and you will be fine
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Unread postAuthor: rad14701 » Fri Apr 13, 2007 6:21 pm

AmYisroelChai wrote:Thats some very logical but contradictaory information to what is beleived on this site. Can you back up that information? How much experience do you have? Have you charted the difference?

I and others are always looking to further our knowledge. But no one wants to waste their money on someones unoroven theories.

I am curious.


Take my advice for what it is, factual information based on close to 40 years of hands on experience in workshops... I'm not some high school kid spouting his mouth here... I've built farm equipment, race cars, cannons, custom rifle parts and silencers, and a whole list of other things... You can toss building a house or two into the mix as well... I'm not concerned with what might be "believed here", I deal with real world logic and "Been there, Done that" real world hands-on experience...
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Unread postAuthor: homedepotpro » Fri Apr 13, 2007 6:31 pm

well i finished the gun

i used the lithium grease and it worked, i needed it because the piston was really tight in the chamber. i also used 2 long screws to attach the sealing face. to reduce the amount of hot glue i use a 1'' male thredded to 1.25 female smooth adapter inside the back of the pistonhttp://www.spudfiles.com/forums/viewtopic.php?p=75510&#75510
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