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Plans for Pengun

Discuss miniature cannons built from things such as pill bottles and pen caps.
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Plans for Pengun

Unread postAuthor: SpaceSpudOne » Sun Mar 30, 2014 3:00 pm

Hello, longtime lurker, first time poster here. On the inspiration of JSR, I've decided to build a pengun. I picked up a 6" long 3/4" Copper pipe, as the air chamber, (I know, not exactly "Pen" size), and a 1/4" OD 8" long copper pipe as the barrel. My piston is going to be a hot glue plug molded from the 3/4" pipe. Will I need to use anything on the sealing side of the piston, or will the glue seal it fine? And the packaging on the barrel says "Soft Copper". Is this ok, or will it flatten due to the pressure? Sorry for all the questions, I'm kind of new to these "Mini's".
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Re: Plans for Pengun

Unread postAuthor: jackssmirkingrevenge » Mon Mar 31, 2014 1:15 pm

SpaceSpudOne wrote:Hello, longtime lurker, first time poster here. On the inspiration of JSR, I've decided to build a pengun. I picked up a 6" long 3/4" Copper pipe, as the air chamber, (I know, not exactly "Pen" size), and a 1/4" OD 8" long copper pipe as the barrel. My piston is going to be a hot glue plug molded from the 3/4" pipe. Will I need to use anything on the sealing side of the piston, or will the glue seal it fine?


A rubber disk is always a good idea. Also, make sure the barrel pipe is not too thin or it will cut into the piston, remember that there is a net force pushing the piston against the barrel. In your case, for every 100 psi there is around 5 lbs for force.

And the packaging on the barrel says "Soft Copper". Is this ok, or will it flatten due to the pressure? Sorry for all the questions, I'm kind of new to these "Mini's".


Not unless you intend to operate at several thousand psi ;)
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Re: Plans for Pengun

Unread postAuthor: SpaceSpudOne » Mon Mar 31, 2014 3:57 pm

Ok, I just finished building it. Now comes the hard part- Waiting for the epoxy to dry :lol: I epoxied a piece of bicycle inner tube to the front of the piston, I think that should seal the barrel quite well. To stop it from digging into the piston, I fit the pipe inside a short bit of 6mm barrel from an old airsoft gun. Here's some pics I took, the blue tape is just there to hold the epoxy until it cures. (EDIT) I tried it today, and the piston wouldn't seal. So, I took it apart, and am going to try the rubber piston. How thick should the piston be?

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Re: Plans for Pengun

Unread postAuthor: jackssmirkingrevenge » Wed Apr 02, 2014 5:40 pm

SpaceSpudOne wrote:Ok, I just finished building it. Now comes the hard part- Waiting for the epoxy to dry :lol:


The curse of the latheless spudder ;)

I epoxied a piece of bicycle inner tube to the front of the piston, I think that should seal the barrel quite well. To stop it from digging into the piston, I fit the pipe inside a short bit of 6mm barrel from an old airsoft gun. Here's some pics I took, the blue tape is just there to hold the epoxy until it cures. (EDIT) I tried it today, and the piston wouldn't seal. So, I took it apart, and am going to try the rubber piston. How thick should the piston be?


half inch at least should be ok.

My advice is to cut it out with a piece of sharpened camber tubing, watch your fingers though ;)

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