SpudFiles

Eh today my first coaxial mini is curing it's in the oven right now, speeding up the process.

EDIT: Jack, do I need to add a bumper onto small coaxials like this???
Right now I have 3 pistons in mind, one that is made out of plastic, very light but might crack after long periods of use, casting one out of hot glue, or casting one out of epoxy. I just want something that will last me a while.

Insomniac wrote:I tried it a moment ago... it maintains structural integrity all the way up to 160psi, and I got about three or four successful pilots from it.. but now the piston ain't sealing right. I used a solid bit of rubber from an eraser, which I think is too soft.

Possibly. Also note how I usually add reinforcement to the breech end of the barrel in order to better support the piston and reduce wear, an important consideration when it is impossible to replace it.

Oh well... I'll stick the arse end of it in hot water to soften the glue and try again!

That's one benefit over epoxy I suppose

Eh today my first coaxial mini is curing it's in the oven right now, speeding up the process.

Mom must be delighted

do I need to add a bumper onto small coaxials like this???
Right now I have 3 pistons in mind, one that is made out of plastic, very light but might crack after long periods of use, casting one out of hot glue, or casting one out of epoxy. I just want something that will last me a while.

Depends on the piston. A solid rubber piston is its own sealing face and bumper so no worries there. If your piston has the potential to damage itself, a simple o-ring the same diameter as the inside of your chamber should suffice.

Well, turns out I was right. My barrel sliced right into my piston. I just tried again with a harder rubber (hot glue is amazing for prototypes!), and it lasted longer but the same thing happens. Interestingly, it maintained functionality all the way up to failure... the only clue that it was cutting through was the increasing delays between piloting and firing. Eventually as I pumped it up it just spat out a barrel-sized cutout of my piston from the barrel. Oh well.

My problem is that I'm using a bit of a teloscoping antenna from an RC transmitter as the barrel... that stuff is THIN, and I didn't add any kind of support around it. Oh well, once I get some more tubing I'll try again.

Insomniac wrote:My problem is that I'm using a bit of a teloscoping antenna from an RC transmitter as the barrel... that stuff is THIN, and I didn't add any kind of support around it. Oh well, once I get some more tubing I'll try again.

There's your problem! Well, either reinforce the breech, or put the seal on the breech itself and you can even use a solid piston.

I think I'll wait till I buy some proper tubing and try again

You use 6mm tube for your penguns don't you? Do you do anything to the schrader to make it fit more snugly first, or do you just use plenty of epoxy to seal the gap?

Insomniac wrote:Do you do anything to the schrader to make it fit more snugly first, or do you just use plenty of epoxy to seal the gap?

Plenty of epoxy though I do sometimes wrap the end with some tape strips to stop epoxy entering the chamber.

Well... I just finished V3 (using the same parts as V1 and V2... the wonders of hot glue!).

I've added considerable support around the barrel for the piston to rest on, and even added heat shrink on the outside to cover the unsightly hot glue which is slowly covering the entire thing. I expect this one to work, and last for at least a little while.

My only worry is that when I shrunk the heat shrink, it melted the glue for long enough for it to drip into the internals. Time will tell!

Here's the latest in the series which I made as a prize for the Fall 2010 best shot contest, still have to make a cap as a firing mechanism, will make some videos then.

thats fantastivly cool

Make a decent video and it could be yours

Here it is in action at 350 psi:

[youtube][/youtube]

Ya know, it would be fun/dangerous to just leave one of those laying around in an office - loaded.


...how do I click this pen...?

Fnord wrote:Ya know, it would be fun/dangerous to just leave one of those laying around in an office - loaded.

Since when was it either/or

Fnord wrote:Ya know, it would be fun/dangerous to just leave one of those laying around in an office - loaded.


...how do I click this pen...?

[youtube][/youtube]



If it wasn't for the fact someone would probably lose an eye, it would be hilarious to try this. Oh well.

Update on the contest pengun, added a cap for firing

looks good, really should make another one of these there quite fun to make