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Proof of concept 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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Proof of concept piston

Unread postAuthor: Panzerfaust » Wed Apr 18, 2007 1:45 pm

Im new to this forum, but have done a fair amount of pvc construction and am looking to upgrade from my current modified sprinkler valve gun. After an 8 month long and bad experience with spudtech.com, ive decided to just get around to making my own piston gun. But before i get into the expense and size of 4" pipe fittings etc. i wanted to make a small proof-of-concept piston gun to make sure i know what i am doing. I plan to make a 3 or so foot long 2" chamber with a 1" barrel. i understand the concept that drives the co-axial piston design, in fact i almost built a 3" end cap piston gun out of dwv parts but decided to wait and make an nsf-pw one. The only thing holding me from making my small experimental gun and a later larger one, is the usual dilemma of what to make a piston out of. I have heard that 1 1/4 end caps fit well in 2inch pipe, and as i dont know of anywhere where i can buy rubber sheet i plan to use a rubber coupler for sealing. i just have a couple things that need to be cleared up before i build anything though. first, i have seen people go through the trouble of making an nsf-pw gun, and then having a cleanout for the back end with holes in it for filling/pilot. as my understanding goes, there is no such thing as a nsf-pw cleanout, so this doesent make sense to me. i would also worry about a piston being able to shatter the end of the gun when it actuates backwards. does this make a bumper absolutely nesecary? my second question is one of how to stabilize the barrel inside the chamber. i have seen cut down reducer bushings used, but i do not see how you would cut them down specifically. i also only have found one confirmed report of rubber couplings used as a sealer face. i had thought of this myself back when i almost mad an end cap piston, but wondered if anyone could confirm that it works. thanks for any and all help.

This is what i plan to build as a final gun. its simple and cheap. Not sure how he cut down that stabilizer with a dremmel though...
http://www.spudfiles.com/forums/basic-coxial-t7413.html
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Unread postAuthor: deusXmachina » Wed Apr 18, 2007 3:03 pm

You can find neoprene in the most random places. Mousepads and certain panholders work really well. And just about anything squishy: nerf balls, pool noodles, tennis balls, mattress foam, all work well as padding for the back of the valve, just make sure they don't get sucked into the pilot
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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: pyromaniac » Wed Apr 18, 2007 3:30 pm

Also as a bumper you can braid three strands of copper wire together then make a spring.
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Unread postAuthor: AmYisroelChai » Wed Apr 18, 2007 3:36 pm

I just read the other thread and asked a bunch of q's go back and see if anyone posts.

Otherwise, people dont use rubber couplings because they just make the piston witha rubber cap attached -cheaper, simpler, and possibly more reliable.

The bushing should fit right into the 4" pipe with no cutting.

OHHHHHHHHHHHHH Stupid me!

The outer lip of the bushing has a "lip" this prevents the bushing from sinking al the way through the pipe. Just cut away or grind down the outer lip.
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Unread postAuthor: Panzerfaust » Wed Apr 18, 2007 4:33 pm

Thanks, il pretty much sum up my long first post into the most important question. Do rubber couplers work as sealing faces? if they did then it seams absurd that people use all these elaborate home made pistons when you could use an end cap, some tape, and a rubber coupler. Also, can any1 confirm that 1.25" end caps make good 2" pistons? And thanks for the bumper material info, but i was more interested in weather they where neccesary or not.
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Unread postAuthor: rad14701 » Wed Apr 18, 2007 4:49 pm

The ingenuity that people have is part of what keeps inventing fun... If everyone built the same gun, the same size, using the same parts, life would get pretty boring pretty quick... Throughout the winter months, when in my area it's too cold and dreary for outdoor activities, I take weekend trips to hardware stores and discount stores looking for ideas... I generally see all kinds of items that, with some imagination and customizing, can be used for purposes other than their original design... Check out the new silicone kitchenware in discount stores... A sheet of silicone can be had for a dollar, for example, and it would yield several piston seals... Imagination is the mother of invention...
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Unread postAuthor: AmYisroelChai » Wed Apr 18, 2007 6:56 pm

Rad --thanx $1 stores -great idea. I forgot about those for silicone parts.
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Unread postAuthor: schmanman » Wed Apr 18, 2007 7:04 pm

I'm not sure If they make rubber couplers that small.

go to your local bell tire and ask for a pooed inner-tube, or buy a cheap one from wal-mart.

as long as you've got a bolt & washer on there, it'll work wonderfully.
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Unread postAuthor: Panzerfaust » Wed Apr 18, 2007 7:20 pm

Bolt and Washer? my main aim is to make a piston that is extremely simple. im going to use end caps. In case i change my mind however, where do you buy those long bolts and huge washers that are used for pistons, i havent seen them anywhere (not that ive looked) i get most of my supplies from lowes as they have the largest nsf-pw pipe section in any hardware store ive seen.

Okay no responses... il ask some other questions that have come up.
People use non pressure rated cleanouts with holes drilled in them for the back ends of coaxial piston guns. Is not it unsafe to bring such a gun to 100 PSI, is it not INSANE to have apiston slam back into at 100 PSI? is it not MORE INSANE to do this after comproising structural integrety by drilling holes in the cleanout?
secondly, in plans such as http://www.spudfiles.com/forums/coaxial-valve-t307.html
wouldent air be able to leak from the inside of the piston past the bolt that holds the sealing face and into the barrel?
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