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Epoxying a copper gun.

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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Epoxying a copper gun.

Unread postAuthor: Mitchza89 » Wed Jan 02, 2008 9:28 pm

I'm looking to make a gun similar to Galfisks piston gun. Through my mate, I'm able to get $145 of materials for 40 due to his staff discount. The only problem is I can't sweat pipe. I don't have the gear to do so. I thought of using some ultra high bond epoxy paste or the normal goop type epoxy. The only thing I'm worried about is when it's epoxied, it's set. no breaking it apart. Hmm...

What does everyone reckon?
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Unread postAuthor: carter » Wed Jan 02, 2008 9:40 pm

gluing together a copper gun. think you shouldn't. might work but it would be better just to buy a propane torch and a few brazing rods and flux. plus if you braze it you can break it down using heat
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Unread postAuthor: Killjoy » Wed Jan 02, 2008 9:40 pm

Actually you can usually break pipes that have been epoxied together by twisted them, Thats how I fixed a couple mistakes I made when I was glueing copper together. But if you do go this route I would recomend trying to find the epoxy designed for copper just to be on the safe side. You shoudl be able to find it in a hardware store.
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Unread postAuthor: Mitchza89 » Wed Jan 02, 2008 9:40 pm

Yeah if not, use compression fittings. Hmm...
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Unread postAuthor: carter » Wed Jan 02, 2008 9:45 pm

i'd go with braze welding. look better. will most likely be stronger. and if you can twist it free i wouldn't like to see what happens when you inject pressure.
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Unread postAuthor: Killjoy » Wed Jan 02, 2008 9:47 pm

I've teasted the epoxy stuff to 150 psi with no failures, but for a sure bet I'd spend the cash and buy a torch and a some flux and solder, the you'll be able to solder the joints and have less worries.
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Unread postAuthor: tylerthetatertosser » Wed Jan 02, 2008 10:34 pm

i epoxy all my copper cannons with crappy dollar store epoxy and i bring them to 200+ psi regularly
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Unread postAuthor: Hotwired » Thu Jan 03, 2008 7:34 am

Eh... you must have a really crappy epoxy if it gives way when the pipes are twisted. Either that or you had a ton of torque on them.

The whole chamber end of my cannon has four pressurised joins using specialised copper/brass epoxy and it's used at 240psi. With proper copper fittings the joins are rated to 500psi.

The only time I could break the joins is in the first few seconds of contact. After about a minute it's cured enough to be immovable by hand.
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Unread postAuthor: Mitchza89 » Thu Jan 03, 2008 7:41 am

Thanks alot the heads up guys. I really appreciate it but eh, I've made up my mind, comp fittings it is!
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Unread postAuthor: DYI » Thu Jan 03, 2008 10:11 am

You do hopefully realize that copper compression fittings aren't available over 3/4", which limits your pipe size to the relatively rare 5/8" copper tubing (since the OD of a standard copper tube is always Nominal Diameter + 1/8").

Just For Copper adhesive produces joints rated for 500 psi (higher than most brass compression fittings), and is extremely simple to use.

On the other hand, a tube of JFC costs $20+, whereas you could buy a torch kit and some solder and flux for about the same price, and get even more use out of it while creating stronger joints.

Unless you plan on using steam as a propellant gas, soldering or JFC is the way to go. Steam use is the only area I know of where compression fittings achieve higher ratings than other methods of joining copper tubes.
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Unread postAuthor: Hotwired » Thu Jan 03, 2008 10:22 am

Actually DYI, specialist places do over 3/4" sizes, B.E.S. in the UK does up to 54mm compression in all standard fittings.

However a 54mm compression coupling will set you back around £20 alone :o

A capillary fitting (soldering) at 54mm costs around £2.50.
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Unread postAuthor: DYI » Thu Jan 03, 2008 2:05 pm

Wow... I've never seen copper comp. fittings over 3/4" anywhere. Not even McMaster :shock:

Of course, McMaster doesn't even carry copper tube or fittings of any sort over 3", so I guess that is understandable. I do, however, have a feeling the Mitchza won't be able do get a hold of comp fittings over 3/4", if he lives in the states.

Soldered or JFCed fittings are a lot cheaper to use than comp fittings in most cases.
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