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Metal Piston-Valved Cannon

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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Unread postAuthor: Anon » Sat Oct 07, 2006 5:17 pm

He said on spudtech he used a end cap for a piston.
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Unread postAuthor: PVC Arsenal 17 » Tue Oct 10, 2006 3:34 pm

yes, what material?
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Unread postAuthor: Velocity » Tue Oct 10, 2006 4:31 pm

It is a pvc endcap, 3/4". Yeah, definitely not idea for winter shooting. But whatever; the worst thing that can happen is the cap cracking (I doubt it would do harm to the metal)

Anyways, sorry I forgot to upload pictures before:


<img src="http://www.spudfiles.com/uploader/uploadFiles/PICT0016.JPG">

<img src="http://www.spudfiles.com/uploader/uploadFiles/PICT0017.JPG">

The barrel is 3' long, made up of 3/4" copper piping. I redid the exhaust system, with a better QEV and a blowgun pilot.
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Unread postAuthor: PVC Arsenal 17 » Wed Oct 11, 2006 2:41 pm

sweet no doubt I'll make one...... that is as soon as I find some cash....
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Unread postAuthor: killagorrila99 » Fri Oct 13, 2006 10:49 pm

Reminds me of my hunting gun. Nice job, have fun and whats the sch of your piston? And what pressure are you using?
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Unread postAuthor: ProfessorAmadeus » Fri Oct 13, 2006 11:09 pm

Is the inside of the pipe smooth. The black iron at home depot or lowes has burs on the inside of it so it couldnt be used for a piston. This reminds me of my gun.
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Last edited by ProfessorAmadeus on Sun Dec 24, 2006 9:33 pm, edited 1 time in total.
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Unread postAuthor: killagorrila99 » Fri Oct 13, 2006 11:14 pm

What? I used metal pipe on my hunting gun and it has burs on the inside but its fine for a pston gun.
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Unread postAuthor: ProfessorAmadeus » Fri Oct 13, 2006 11:19 pm

Really? i would think it would make it hard for the piston to move. Well i guess it works.
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Unread postAuthor: Can-O-Man » Sun Nov 26, 2006 4:40 pm

very nice gun. $20 is a good price. keep up the good work
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Unread postAuthor: frankrede » Sat Aug 25, 2007 6:42 pm

Rmich, what does your piston seal against?
and if you could do me a big favor, would it be possible to see the insides of the piston valve?
I am currently making a metal cannon and I am stumped when it comes to making a piston for a threaded metal T.
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Unread postAuthor: Velocity » Sat Aug 25, 2007 7:47 pm

Yeah, I definitely should post pictures of the internals of this gun. I have had over ten people ask me (by PM) how this thing actually works.

I don't have a picture of the piston (it was just two 3/4" endcaps solvent welded together with a piece of neoprene at the end), but I do have the body of the cannon. The piston seat was welded black iron, so yes, there was a welding seam (a big one too). I wrapped a layer of duct tape on the inside of the piston seat, and a layer of duct tape around the piston. I then put some grease between them, and it worked pretty well.

I'll try to post pictures soon (within the week), but I gotta find the camera, memory, and cannon first.
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Unread postAuthor: Velocity » Sat Aug 25, 2007 8:05 pm

Alright... finished a little earlier than I thought, so here are some pictures

<a href="http://i94.photobucket.com/albums/l112/rmich732/WholeCannon.jpg">The whole cannon</a>... it really is a shame that it was only fired about five times in total, considering that it has gotten me more questions than any of my other projects.

<a href="http://i94.photobucket.com/albums/l112/rmich732/ReverseBushing.jpg">Here</a> is the front side of the 1.25" x 3/4" bushing. If you look into the 3/4" hole, you can see a metal tube at the very bottom which extends out of the 3/4" hole. That tube is actually a 3/4" iron pipe nipple. I simply threaded it into the wrong side of the bushing, and then added epoxy for extra strength. It only had about two complete turns, but with the forces acting on it, combined with the addition of epoxy, I was really never worried about it. Besides, I had a PVC piston, which would undoubtedly break before the metal parts did.

<a href="http://i94.photobucket.com/albums/l112/rmich732/Bushing.jpg">Here</a> is the backside of the bushing. You should notice the PVC. I cut a 3/4" PVC coupler in half. I then added epoxy to the inside of the 3/4" PVC coupler and to the outside of the exposed 3/4" threaded iron pipe nipple (the exposed portion of the nipple was 80% of it, because only a small portion of the nipple was screwed into the wrong side of the bushing). I then pushed them together, with great aid from a rubber mallet. Finally, I put some contact cement on the face of the 3/4" coupler (which had the 3/4" nipple in it), and put a rubber sealing ring on. Easy. The reason I added the coupler was to provide a greater area for the rubber sealing ring to stick to.

There you go guys... the "secret" is out. It was a very simple process, and I only did it because it was easy. I soon made a copper piston rifle, and I never went back. Sure, this method is easier and cheaper than making a copper piston rifle, but let me tell you, a copper rifle looks better, performs better, is lighter in weight, holds more pressure (no threads) and is more ergonomic as well. Spend the extra dollars and get yourself some copper. It is a much better option.
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Unread postAuthor: noob of noobs » Sat Aug 25, 2007 9:57 pm

Huh... Thanks. I myself am also building a metal piston valve, (well, actualy, it uses a lot of PVC parts) but I might try something like your's for an upcoming gun. It's kind of an artillary cannon, and will probably need 2 valves. About how much would a 2" copper piston valve cost do you think?
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Unread postAuthor: frankrede » Sun Aug 26, 2007 12:12 am

a 2" copper fitting would cost maybe 15$?
They are not cheap:(
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Unread postAuthor: Velocity » Sun Aug 26, 2007 1:16 am

Copper is really only a good option for 1" and below; after that, it gets really expensive. Frankrede, did this explanation answer your questions?
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