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A question about making a mini coaxial

Discuss miniature cannons built from things such as pill bottles and pen caps.
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A question about making a mini coaxial

Unread postAuthor: Jose Arcadio Buendia » Sun Dec 22, 2013 8:14 pm

This is my first, but unfinished mini coaxial piston pneumatic:
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The chamber is made from 1/2 in. sch. 40 PVC pipe. The barrel is the body of a bic pen. I used the neck of a soda bottle on the end to have a good access to the piston. I hot glued to the barrel a peice of drinking straw to keep it centered. I attached to the soda bottle cap a brass fitting with 1/8 in. tube to connect it to a shrader valve from a tire tube, which I have to find because I misplaced it. I plan on using it at 80 PSI and after it works extending the barrel by adding two more pen bodies to the barrel. I plan on using for the piston a piece of a hot glue stick with tape around it for a tight fit with a piece of tire tube to seal the barrel. The question I have is: how much moving space should the piston have?

Edit: This is the piston:
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Re: A question about making a mini coaxial

Unread postAuthor: jackssmirkingrevenge » Tue Dec 24, 2013 10:41 am

Cruide but it might just about work :)

Jose Arcadio Buendia wrote:The question I have is: how much moving space should the piston have?


You don't need a lot for full flow, calculate around half your barrel diameter, about 1/8" should suffice in your case..
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Re: A question about making a mini coaxial

Unread postAuthor: sagthegreat » Tue Dec 24, 2013 11:06 am

is that piston made out of a watermelon? o.0 lol
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Re: A question about making a mini coaxial

Unread postAuthor: Jose Arcadio Buendia » Tue Dec 24, 2013 3:20 pm

I did some testing and finally got it to work. I couldn't go above 60 psi because above that the connection between the hose and the compressor can unexpectedly disconnect.
Heres a video:



I had to change the piston for a molded hot glue piston and add a spring.
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I put steel wires to keep the bottle neck in place and applied epoxy to the cap and barrel.
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Last edited by jrrdw on Wed Dec 25, 2013 8:09 am, edited 1 time in total.
Reason: Fixed video.
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Re: A question about making a mini coaxial

Unread postAuthor: PeteS » Wed Dec 25, 2013 9:26 am

Looks like a fun project.

Can you tell us a bit about that compressor. Is it cordless? 12v? How much pressure will it deliver?

Most of the little 12v compressors are complete junk, but I'd really like to have one that was decent. That or a cordless one. My wish list would be 150 psi and at least moderate volume. I have had some that claimed 250 psi and then delivered something like 30 psi. On one the gauge was so bad that it showed over 100 psi when it was actually at 30 psi!
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Re: A question about making a mini coaxial

Unread postAuthor: Jose Arcadio Buendia » Wed Dec 25, 2013 1:44 pm

PeteS wrote:Can you tell us a bit about that compressor. Is it cordless? 12v? How much pressure will it deliver?

It is cordless. It uses detachable 18v batteries(ryobi one+ system) that are interchangeable with other electric tools. It is supposed to go up to 150 psi, however I don't know how accurate the gauge is or if the max pressure is true. It is not a good compressor; the compressor's schrader valve connector is not well built since it doesn't connect well; this causes leaks or unexpected disconnections. Also, I left the compressor by a window with thin curtains, so it took like 2 hours of mild sun light; I went to use it and it marked error on the gauge, but after it cooled down the gauge worked normally.
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Re: A question about making a mini coaxial

Unread postAuthor: PeteS » Wed Dec 25, 2013 8:12 pm

Thanks. I won't bother looking at that one then.
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Re: A question about making a mini coaxial

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