Posted: 05/02/2006 15:44 PM Post subject: Micro Pneumatic Coaxial
WITTY PHRASE
Joined: 27 Mar 2006 Posts: 1235 752.27 Spud Bux
It's finally done! Here is my micro pnematic cannon. It's only a foot long but pretty powerful. The main chamber is 2 3/4 inch cleanouts and a 3/4 inch coupling. A length of 3/4 pipe runs inside from end to end. The front end is made of copper and brass fittings with a brass barrel. There is a Presta valve threaded into a cap and JB Welded. The Presta is great because it's really small and doubles as the trigger. You just push the knob on the back to fire. The diaphragm was punched out of a rubber sink stopper using a sharpened 3/4 copper sleeve. My primary ammo is bb's but k'nex rods make for some devastating little spears. Hope you guys like it!
The diaphragm must seal against the barrel. That is very important. It does not have to seal against the chamber walls and it should actually be a little smaller than the walls in diameter so it has room to flex in and out. In must also seal against the fitting screwed in behind it, in this case a 3/4 inch nipple. If it doesn't seal well against it, the air in the main chamber can leak out the back when fired, causing less air to go out the barrel where it is supposed to. I covered my diaphragm in a little dap of hand soap so it seals better.
This actually isn't my smallest micro pneumatic, I made some with an orange pill can and a pen tube for a barrel. The diaphragm was piece of inner tube and it rested against a bottle cap that was glued in with a big hole drilled through it. The can's cap was also glued and had a tire valve in it. It actually worked until the glue stopped holding. Here is a simple little diagram I made of it a while ago.
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