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Building First Piston Gun. Pics included

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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Building First Piston Gun. Pics included

Unread postAuthor: glass_05 » Sun Apr 27, 2008 7:15 pm

I'm building my first piston gun. im going for a co-axial b/c i read those are easier. ill let the pics explain the rest..

here is the whole gun. with a 2inch barrel 4inch chamber
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the rear end. im especially happy with how the filling system works during my test fills. just hook the line up and turn the knob.
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next 2 pics are off the piston. the piston does slide up the chamber when i turn the air on so that is good. but im afraid if it will seal or not. the material i am using is softish and i have 4 layers. i found it in my garage.
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last is my future plan for the gun. once i get it all working ill cut off the 2inch barrel and turn it into an over-under gun with my 2.5inch barrel so i can shoot tennis balls.
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Last edited by glass_05 on Sun Apr 27, 2008 7:32 pm, edited 1 time in total.
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Unread postAuthor: biggsauce » Sun Apr 27, 2008 7:20 pm

Looks like a start, but what are the endcaps made of? They don't appear to be pressure rated in the pictures...

You're gonna catch crap for the DWV elbows...

Edit: and the bell reducer... no good borther. The endcap for the piston shouldnt be a problem, but I would change out that endcap, aspecially if you plan on holding this thing.

And did you get the chamber from a construction site??
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Last edited by biggsauce on Sun Apr 27, 2008 7:23 pm, edited 1 time in total.
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Unread postAuthor: glass_05 » Sun Apr 27, 2008 7:22 pm

the endcap is the only one the store had. i just figured it was pressure rated.

whats wrong with the elbows?

and the chamber came from my friends farm
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Unread postAuthor: biggsauce » Sun Apr 27, 2008 7:26 pm

The elbows also aren't pressure rated. Although they will be used in your futre barrel(?) I would steer clear of them.

Although I'm not 100% sure that the endcaps aren't pressure rated, they look like it.

Is there any lettering on the endcaps? If so, what does it say?

Edit: sorry to rain on the parade, but for a pneumatic cannon, these parts are unsafe. Trying to save you from the ER man
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Unread postAuthor: glass_05 » Sun Apr 27, 2008 7:30 pm

i figured the elbows would be okay since they are not holding any pressure, only when the gun is fired.

and its just encap, not caps. i will only be using one on my gun. and i just check and you cant see the wording because of the holes i drilled and the parts put on it
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Unread postAuthor: biggsauce » Sun Apr 27, 2008 7:37 pm

Do you have a Home Depot or a Lowes around where you live? They will hace pressure rated parts. The endcap, reducer, and elbows are DWV rated (drain, waste, vent) are designed for gravity flow pressure only.

The endcap you want to use should be rounded, not flat like yours is. Ever seen a compressor tank with a flat side?

Spend the extra money and keep yourself safe
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Last edited by biggsauce on Sun Apr 27, 2008 7:38 pm, edited 1 time in total.
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Unread postAuthor: MrCrowley » Sun Apr 27, 2008 7:38 pm

Woah, never ever think it's pressure rated because it's the only one they have. This hobby is very dangerous, and using DWV like you are, you could lose an eye.

Read this:
http://www.spudfiles.com/spud_wiki/inde ... _Rated_PVC

The larger elbows aren't pressure rated, same with the bell reducer and end cap. I'm not sure about the chamber, you'll have to read the above article I wrote and see if it has the correct markings.
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Unread postAuthor: glass_05 » Sun Apr 27, 2008 7:38 pm

ok. ill look into that. what do you think of my piston. is it going to seal?
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Unread postAuthor: biggsauce » Sun Apr 27, 2008 7:39 pm

Ah thanks MrCrowley, much better said

If the the edge of the barrel that your piston seals against is cut true and smooth, you shouldn't have trouble sealing
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Unread postAuthor: glass_05 » Sun Apr 27, 2008 7:43 pm

that article was of great help. and i know for a fact the chamber is pressure rated.
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Unread postAuthor: MrCrowley » Sun Apr 27, 2008 7:48 pm

As biggsauce said, as long as the piston is a good fit, IE you can push it with your finger, you should be fine. But it has to be a really good fit, like if you put it inside the pipe and looked inside, you shouldn't see much if any light coming from the edges of the piston.

Make sure to use some sort of lubrication as well, just ask for some plumbing lube at a hardware store.

Also do you have a bumper? By the looks of things, your piston is going to slam into those fittings in the end cap and eventually knock them out. Even if you do the same with the pressure rated end cap, it will fracture the pipe.

Make sure there is adequite protection so the piston doesn't slam into them and make sure you have a good bumper.
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Unread postAuthor: glass_05 » Sun Apr 27, 2008 7:50 pm

i was planning on getting a can of great stuff and spraying it in the back of the endcap and cutting it away leaving some to act as a bumper
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Unread postAuthor: biggsauce » Sun Apr 27, 2008 8:04 pm

That may work, even though it might have the tendency to crush and compact over time.

Try a pice of garden hose. Also if the Great Stuff doea begin to crush and break, pieces of the foam may end up in the diaphram of your sprinkler valve, which might affect its ability to seal
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Unread postAuthor: JDP12 » Sun Apr 27, 2008 8:11 pm

you can get pressure rated fittings on mcmaster- they're called NSF 61 however..
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