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First coaxial piston gun

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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First coaxial piston gun

Unread postAuthor: cornflake_81 » Wed Apr 16, 2008 2:51 am

I've been fighting wi-, er, um.. working on this one for a couple of weeks now. The previous iterations of this gun featured non-serviceable pistons, which ultimately were a bad idea. I'm building this as a learning tool, so to speak...to better understand the ins and outs of a piston valve. So, a serviceable piston was a must. I've gotta say, apparently the third time's a charm, 'cause this one actually works quite well. On to the specifics...

The chamber is 2" sch 40 and the barrel is .75" sch 40. The business end is just a 2"x.75" reducer bushing with the flange dremel'd out of it and the barrel (sloppily) welded flush.

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To keep the barrel centered, I again dremeld the flange out of a 1.5"x.75" reducer bushing and cut small wedges out of it. A little epoxy to hold them in place and it works nicely.

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The piston (which I had previously described <a href="http://www.spudfiles.com/forums/sanding-drum-piston-t14066.html">here</a>) is the rubber cylinder from a 2" sanding drum and a handful of nuts, bolts and washers. I scrapped the inner tube sealing face in favor of a 2" neoprene washer, which works much better.

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Finally, a couple thread adapters (I didn't know they made those nsf-pw...pleasant surpise, indeed), .75" sprinkler valve/blowgun, schrader valve and a guage. (please forgive my messy workbench)

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Despite a little sloppy primer work, I'm pleased. All I wanted was a simple little plinker to fool around with. Just with the few low pressure shots I've made while testing the piston, I've been surprised by the "thump" this thing produces. I'll put it through its paces tomorrow. I have to admit, however, this is one of the smaller guns I've built and I'm a little dubious as to what kind of pressure it will take.

Either way, lemme know what you think. I know there must be some obvious short-comings, and I wanna know what they are so the next one will be better. I'll try and get some video up tomorrow, as well.
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Unread postAuthor: psycix » Wed Apr 16, 2008 4:17 am

Whoa that looks very very much like my pneumatic!
Even the barrel spacers are the same lol :D
I like it!
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Unread postAuthor: jrrdw » Wed Apr 16, 2008 6:48 am

Nice build cornflake_81. This is also (in my opinion) a good basic "how to". Newbies wanting to build piston valve's should take a good look at this.
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Unread postAuthor: Tom » Wed Apr 16, 2008 8:20 am

I like it to, very clean.
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Unread postAuthor: XxtriviumxX » Wed Apr 16, 2008 8:32 am

Nice, that is very clean, Im hoping to make a Coaxial some time soon :)
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Unread postAuthor: bigbob12345 » Wed Apr 16, 2008 8:40 am

Nice job
How heavy is that piston and how much would a 2in sanding wheel cost?

and i think it needs a paint job
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Unread postAuthor: biggsauce » Wed Apr 16, 2008 8:46 am

Alright, I like it! Clean clean clean, brother. I bet the power of that thing will suprise you.

Do you have to use any sort of lubrication on the piston? Seems like the rubber might keep it form actuating as fast...

As far as pressure, it sounds like everything is pressure rated, so you should be safe taking up to what your vavle is rated to. Probably 120?

Anyway, nice cannon, try shooting some full 12g co2 cartriges at something solid. Say cinder block? :P
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Unread postAuthor: starman » Wed Apr 16, 2008 10:25 am

Man you put that sanding drum to work fast didn't you. The piston looks like the perfect fit in there and the adjustable nature of it makes it almost ideal.

If you've got the barrel sealed well and piston optimized, this thing will carry more punch than you might think. Nice job!
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Unread postAuthor: cornflake_81 » Wed Apr 16, 2008 11:00 am

psycix wrote:Whoa that looks very very much like my pneumatic!
Even the barrel spacers are the same lol :D
I like it!


Thanks. I researched several guns on this site and took pointers from all of them, so this should look familiar to a few people.

jrrdw wrote:Nice build cornflake_81. This is also (in my opinion) a good basic "how to". Newbies wanting to build piston valve's should take a good look at this.


Thanks, jrrdw. I took a lot of pictures and explained it in a lot of detail so it might help someone else. I know I initially had a hard time wrapping my brain around how exactly a piston valve works.

bigbob12345 wrote:Nice job
How heavy is that piston and how much would a 2in sanding wheel cost?

and i think it needs a paint job


The piston wights 5.75 oz. with all the hardware attached. I actually got it in a set of four sanding drums at Harbor Freight (God bless Harbor Freight) for $7.99. Not a bad price, plus I still get to use the other 3. :D Still have a few modifications to make and then I'll paint it.

biggsauce wrote:Alright, I like it! Clean clean clean, brother. I bet the power of that thing will suprise you.

Do you have to use any sort of lubrication on the piston? Seems like the rubber might keep it form actuating as fast...

As far as pressure, it sounds like everything is pressure rated, so you should be safe taking up to what your vavle is rated to. Probably 120?

Anyway, nice cannon, try shooting some full 12g co2 cartriges at something solid. Say cinder block? :P


Thanks, man. I tried white lithium grease at first which didn't seem to work too well. I wiped it down and gave it a few spritzes of silicone spray and it slides as smooth as you could ever want it to. I may have to pick up a pack of co2 cartridges tonite... :idea:

starman wrote:Man you put that sanding drum to work fast didn't you. The piston looks like the perfect fit in there and the adjustable nature of it makes it almost ideal.

If you've got the barrel sealed well and piston optimized, this thing will carry more punch than you might think. Nice job!


Yeah, I try not to let a good idea go to waste. Thanks.
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Unread postAuthor: sniper hero » Wed Apr 16, 2008 11:22 am

cool gun it's .. it's it's so clean :D
I really like the piston
I would love to have a piece of rubber like that

and it would be handy if you make a list of specs like this

chamber volume:
barrel lenght:
speed of projectile:
etc.
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Unread postAuthor: cornflake_81 » Wed Apr 16, 2008 2:57 pm

sniper hero wrote:cool gun it's .. it's it's so clean :D
I really like the piston
I would love to have a piece of rubber like that

and it would be handy if you make a list of specs like this

chamber volume:
barrel lenght:
speed of projectile:
etc.


Thanks. Honestly, I threw this thing together from a few spare pieces of PVC and didn't pay much attention to volume's, rations, etc. I'll try to figure them out though. I did finally get a chance to fire it today and, I gotta say, its got some oomph.
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Unread postAuthor: taytayswims » Sun May 04, 2008 10:54 pm

what is the size of the nipple you used for the bow gun?
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Re: First coaxial piston gun

Unread postAuthor: watto » Wed May 07, 2008 10:33 pm

I notice your work bench is a bit messy...clean it or I wont forgive you :lol:

















cornflake_81 wrote:please forgive my messy workbench
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