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mini coaxial

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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mini coaxial

Unread postAuthor: hi » Tue Apr 03, 2007 10:44 pm

this is my mini coaxial. It has a 1'' chamber that is about 11 inches long. The barrel is 1/2 inch pvc and it about 8 -9 inches long. The piston is a dowel and has a piece of rubber bolted on the front. The fill valve/ exhaust valve is a 1/4'' ball valve with a quick release for a compressor. I need to make a new piston because sometimes this one seal and sometimes it doesn't. when it does it is fun to shoot marbles and AA batteries.



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Unread postAuthor: jackssmirkingrevenge » Tue Apr 03, 2007 10:48 pm

Why is the brass pipe at the pilot end so long? That's extra pilot volume which you could reduce and make it more efficient.
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Unread postAuthor: noname » Tue Apr 03, 2007 10:50 pm

Mini? Bah, that thing is enormous!
I'll show you mini....just give me a week or two. :D
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Unread postAuthor: hi » Tue Apr 03, 2007 10:52 pm

Thats what someone on spudtech said. it not a brass pipe, its a 3'' copper nipple.

Noname- good luck on making a working piston gun smaller than mine.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 03, 2007 10:53 pm

noname wrote:Mini? Bah, that thing is enormous!
I'll show you mini....just give me a week or two. :D


Now that's a mini-coaxial ;p
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Unread postAuthor: noname » Tue Apr 03, 2007 10:56 pm

It won't be a piston gun, I prefer diaphragms over pistons. I was actually planning on making identical guns, but one of them was to be a mini diaphragm gun, and the other is going to be a strafer. Both of them will be a 3/4" coupler with plug, a short piece of 3/4" PVC, a female coupler, and a threaded plug.
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Unread postAuthor: Hawkeye » Tue Apr 03, 2007 11:30 pm

Are a Piston and a Diaphragm really worth differentiating if they are both barrel sealers?
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Unread postAuthor: hi » Tue Apr 03, 2007 11:36 pm

yes they are worth differentiating because they are totally different.

they work on the same idea. A piston is a piston shape and a diaphragm is a piece of rubber that seals against the barrel. they are in the same spot, but they are different.

To explain a little better, a diaphragm is a piece of rubber that sits between a union and seals against the barrel, if that helps.

a sprinkler valve uses a diaphragm valve just so you know what it is.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 03, 2007 11:45 pm

I think he knows what it is, but was trying to point out that on such a small scale, performance between diaphragm and piston valves won't be that different.
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Unread postAuthor: A-98 » Wed Apr 04, 2007 12:10 am

jacks, is it me or is that epoxy? if it is, you extremely gifted with the stuff, cause it seems that all your ingenious little things are made out of the stuff.

besides, give me government funding and acces to caltech machine shop an i'll show you mini!

nice gun hi, i think i saw it on spudtech.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 04, 2007 1:23 am

A-98 wrote:jacks, is it me or is that epoxy? if it is, you extremely gifted with the stuff, cause it seems that all your ingenious little things are made out of the stuff.


Yes it is, extremely versatile material - can be frustrating to work with but it does offer a lot of possibilities that standard fittings don't. It's not cheap, 9 lbs of the stuff cost me around $100 but I bought it 3 years ago and still have half the containers left so the cost per project is minimal.
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Attachments
minipistondia.JPG
this is what the internals of the above coaxial look like
hvbb.JPG
my current mini coaxial design, without the completely airtight piston which removes the need for an equalisation tube and check valve.
hvbb.JPG (32.48 KiB) Viewed 872 times
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Unread postAuthor: noname » Wed Apr 04, 2007 6:08 pm

Diaphragms aren't always in a union, hi. I've made three diaphragm coaxials, and I've never even though of doing that.
Hawkeye, the difference is: diaphragms are extremely compact, and don't need travel space, but one of this size will still perform the same.
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Unread postAuthor: subterranean » Wed Apr 04, 2007 6:25 pm

wow "hi" im building something very similar and was just about to post it, but im having the same problem. Im using 1/4" brakeline(i cut the flaring off of the piston sealing end) in a 1/2"pvc chamber. I have made 4 different pistons all better but not with a good barrel seal.
1- rolled duct tape with bike tube rubber disk to seal it.
2- hot glue piston
3- rolled duct tape with a concave head filled with silicon.
4- dowl with electric tape to seal it(worked OK) but for a mini NO way.

Each design had a slight leak on the sides to fill the chamber.
Is there any good way to make a mini piston or should i call it quits!?
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Unread postAuthor: hi » Wed Apr 04, 2007 6:57 pm

Dont give up, its just that really small ones are hard to make work. The hot glue piston should work if it fits in the chamber well. do they have a rubber disk on them. if the disk is thin them put two on. Use a double thick inner tubes from a bike, thats what i used. Just make sure that it fits well in the chamber.

A really good way to make a piston fit well is wrap painters tape around it and put a little gun oil on it. Why painters tape? because it low friction and it works.
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Unread postAuthor: subterranean » Wed Apr 04, 2007 7:03 pm

Are you allowing a slight leak around the piston and the chamber to fill the rest of the chamber or do you have a different method?
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