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plywood piston

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: Velocity » Sat Oct 21, 2006 3:39 pm

djt wrote:i think hes trying to say 923 pounds of force because it would be 100 pounds PER square inch. but i doubt you would have 9 square inches


kinda random, but I believe you mean "she's"
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Unread postAuthor: POS » Sat Oct 21, 2006 4:08 pm

schmanman wrote:jrrdw did it without a problem.


Yeah, but at what pressure. I made a piston out of a bolt, rubber, a plastic tube and some tape to make the whole thick enough. It waighted about 20 grams. Behind the piston was a smaller tube and a spring as some sort of bumper. When I fired the gun several times at 9 bar, the piston didn't get back to sealingposition. The spring was broken. When I opened the gun, I saw that the spring was all smashed up by the piston, ans was pressed in the smaler tube. I mean IN the tube, not inside the tube. The tube was deformed completely. It was of copper though, but nevertheles. When the tube and the piston gets dammaged at 9 bar, I dont think a wooden piston would survive more that 5 bar (70 psi)
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Unread postAuthor: Infernal2 » Sat Oct 21, 2006 5:15 pm

Those small sheets of wood layered are exactly what I'm talking about.
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Unread postAuthor: Infernal2 » Sat Oct 21, 2006 7:32 pm

POS, my coaxial marble gun regularly exceeds 100 PSI (not past 110 PSI) and its solid oak. However, I'm using a rather strong spring as a bumper to prevent rear impact. Standard pressures are enacted on this piston though.

To be honest, I'd say my wooden piston is probably the least troublesome of the pistons I've built. It was simple to produce, easy to cut o-rings in, and VERY little work; it has outperformed my others.

You may have been talking about plywood though.
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Unread postAuthor: POS » Sun Oct 22, 2006 4:08 am

about any wood. Bot as you said, a very strong spring could salve much. But then you have to make the pilot volume larger to, don't ya ?
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Unread postAuthor: boilingleadbath » Sun Oct 22, 2006 7:50 pm

IIRC, the tensile strength of hardwoods can approch 3000 PSI in optimal conditions.

Now, it's a directional substance, plywood isn't hardwood, and that number varies with humidity... but I'd expect atleast 1,000 PSI out of plywood.

UHMWPE has a UTS of ~3000 PSI, and PVC comes in at ~7500 PSI, and neoprene [rubber] is about 1000 PSI.
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Unread postAuthor: POS » Mon Oct 23, 2006 6:13 am

yes, ok, pressure, and movement by pressure are two diferent things.

When the wood shoots back with a pressure of 1000 psi, en sudenly smash into something (stopper) it could break.
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Unread postAuthor: joannaardway » Mon Oct 23, 2006 6:39 am

i think hes trying to say 923 pounds of force because it would be 100 pounds PER square inch. but i doubt you would have 9 square inches

1) Rmich732 is correct - you hopefully meant to say "She's".
and
2) No, my figure was perfectly correct. 85 pounds of force (The resultant force from a piston inside 28mm copper pipe sealing against 22mm copper at 10 bar [a not uncommon pressure for copper]) split over an area of 0.09 square inches (the cross sectional area of the actual sealing face when you seal against 22mm copper pipe) is equivavlent to about 932 psi.

Do the numbers yourself.
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