SpudFiles

After seeing some of the mini coaxials posted lately, I decided to get off my ass and make one.

I originally intended this gun to be fired via a schrader valve, and when it refused to fire I assumed the piston was at fault. After going through several pistons, I decided to try a bigger pilot. I stole a T and schrader from my ball valve gun, and attached a pvc valve I had laying around and tried it . IT WORKED!!!! Because of the unplanned modification to the design, the piston has loads of travel because the rubber bulb of the schrader no longer takes up part of the chamber, and there is loads of dead space in the T, but I think the pilot makes up for it

The noise from the T venting through the pilot is louder than the actual gun firing

The gun is made of threaded poly pipe and has a 6mm pen tube epoxyed into the brass cap. The reason for the funny adapter is so I could use a cap with threads on the outside, letting me glue it without ruining the threads. The piston is made of a small plastic bottle I had, chopped in half and with a bit of bicycle inner tube epoxyed to it (is it epoxyed or epoxied? Epoxied makes more sence, but then you are changing the name of the glue, which makes it incorrect... hmm.... )

After a few test fires the sealing face came off, So I am currently gluing it back on. I might switch the fill valve and the ballvalve around, so that if I look along the barrel I don't get a facefull of air, and possibly a piston if it manages to slip through the lip that stops it (not too risky, seeing as I always wear safety glasses) The piston lacks a bumper but other than somtimes getting stuck it doesn't seem to be a problem. I think what I might do is get some 6mm brass tube, and make the piston travel smaller, the barrel and chamber longer, and keep my over-the-top pilot setup. I'm using it at around 150+ psi, I pump as high as I can with the bike pump.

I will post pictures in a moment. I tried to a few minutes ago but spudfiles gave me an error and I lost my post So I'll post this now and then add pics.

The gun:


Semi-expanded view, minus piston (is gluing)


The massive pilot valve


The piston. Very light.




Damage from a white k'nex bit at a wooden domino.


This is the gun in it's intended layout, which was a failure due to insufficient pilot.

hey mate

there is no point me posting mine now then (jj it will be up)

i made one just like it but with a 3/8" qev as pilot but went on holls so havnt finished lol

nice job though

Nice mate, Very nice

This thing is starting to annoy me.... I need a way to stop the piston flying back into the T, and I also need a way of making the piston longer... it has sooo much travel and I imagine a lot of power is lost moving the piston... I tried putting some plastic to stop the piston going into the t, and another piston behind the main one to reduce the travel, but the pistons smashed right through the plastic. I tried again with better plastic but now the double piston setup refuses to actuate. I think I will have to cut a bit of metal in the shape I need to stop the piston entering the T, and find a longer piston.

You could glue a washer on the insde of the tee connecting to the pipe. Or in the nipple connecting the pipe to the tee. That is assuming your using a nipple.

The pipe itself is threaded, but I've found a solution. One of the pistons fits so well it refuses to come out one end of the pipe because of a tiny tiny lip at that end... like, really tiny lip. To reduce the travel I have glued up another piston that I should be able to put infront of it, reducing travel (It will be dry in a few hours). This way the current piston will basically act like a bumper.