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piston fit/ OD tolerence

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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piston fit/ OD tolerence

Unread postAuthor: turner » Wed Apr 20, 2011 5:34 pm

do you think a delrin piston that is .75 would be a good enough fit for drawn aluminum tube at .759? this if for a coax rifle and i would like to use a small valve like a blowgun.

Or do you think i should go with the .120 wall thickness and turn the plastic down on the school wood lathe. floating o rings would be easy, but how close can you turn the OD to using a caliper?
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Unread postAuthor: Technician1002 » Wed Apr 20, 2011 6:03 pm

Is this Feet, Yards, Meters, Angstroms, mm, etc. Units of measure would be helpful.
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Unread postAuthor: metalmeltr » Wed Apr 20, 2011 6:07 pm

.009" isn't much. A sheet of computer paper is between .004" and .005". The paint on your car is about .003" thick. Long story short i think you will be fine.
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Unread postAuthor: turner » Wed Apr 20, 2011 6:12 pm

oh its in inches, i just want to make sure cause other parts i have measured made on lathes are like .002" do you have any idea on the tolerances i could make on a wood lathe with plastic? Ive never used it, but it seems like it wouldn't be that accurate.
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Unread postAuthor: metalmeltr » Wed Apr 20, 2011 6:28 pm

You would be lucky to get it within several thousandths.
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Unread postAuthor: Technician1002 » Wed Apr 20, 2011 6:29 pm

Taking lite passes and monitoring progress, reasonable tolerance can be done. I get very close using a drill press.

http://www.spudfiles.com/forums/tutorial-making-a-small-o-ringed-piston-on-a-drill-press-t21740.html

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Unread postAuthor: turner » Wed Apr 20, 2011 6:46 pm

Ive made smaller pistons on my drill press, but i never get the the arbor in strait and it seems like o ring groves would be a pain. maby i should just try it with a .009" gap
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Unread postAuthor: Technician1002 » Wed Apr 20, 2011 6:54 pm

Use the drill press vise to both drill the plastic for the arbor and then again to align and screw in the arbor. After drilling, leave the plastic on the drill press vise. Replace the bit with the arbor in the press and hand screw it in using the press for perfect alignment. You can open the top of the press, remove the belt, and hand turn it in.
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