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A few copper questions

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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A few copper questions

Unread postAuthor: iisthemuffin » Fri Jun 13, 2008 10:59 am

Im thinking of building a copper piston cannon when i get my job. So first of i was wondering how much psi would one of the already made copper tanks hold? (pictured here on this gun)

Also he speaks of it shooting well for having a small chamber volume. Will someone please explain this concept to me? i think i understand the basics of it but i just want to be sure. Would this be a good decision for a chamber on a copper gun?

I read alot aoubt soldering copper. Is that just like regular solder? Because what i have is a soldering gun that you heat the pieces with and then lay solder? My gun is about the size of a screwdriver. I have only used solder for copper wire, so i was wondering if this would be enough to hold pressure?
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Unread postAuthor: LikimysCrotchus5 » Fri Jun 13, 2008 11:10 am

There are three types of copper, type L, M, and K.

M is the thinnest, K is the thickest, and L is medium.

It can hold a good deal of psi. Its use pressure is like 300-450 i think but its burst pressure is 1.7kpsi for type M IIRC. Obviously type L and K have a higher pressure use and burst pressure.

Whats good about copper is that you can put alot of pressure in it, which means more air which means more power that is available.

iisthemuffin wrote:I read alot aoubt soldering copper. Is that just like regular solder? Because what i have is a soldering gun that you heat the pieces with and then lay solder? My gun is about the size of a screwdriver. I have only used solder for copper wire, so i was wondering if this would be enough to hold pressure?


I find that being contradictory. If you read alot about soldering copper pipe, you would know that you dont use a solder gun like for electronics, but use a propane torch and flux.

You may have to do a little more reading.
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Unread postAuthor: iisthemuffin » Fri Jun 13, 2008 11:15 am

I did not mean i read alot on how to do it. I meant i had seen alot of posts about about people using solder. Im sorry for the missunderstanding. I probably should have been more clear
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Unread postAuthor: LikimysCrotchus5 » Fri Jun 13, 2008 11:18 am

Its ok, so now you know :)

I am making a copper gun as well, sometime soon :roll:

I do have the copper parts, but i have never soldered although i have read about it and i also need to find a piston.

Its not a big deal though, just making sure you know whats correct.
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Unread postAuthor: iisthemuffin » Fri Jun 13, 2008 11:21 am

Thank you for telling me. Once again i apologize for the poor explanation on my part. I have never built a piston cannon before and know little about piloting and flow restriction. What would you recomend using as a pilot valve? Im most likely going to be using the canister i spoke of in my first post for a chamber and it will be used for marbles. I have a diagram atached of the design i am thinking of. And please dont mistake this as me asking you to help me design my cannon. I am simple just asking your advice in a pilot valve.

EDIT - im drawing th diagram right now so it will be a sec
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Unread postAuthor: sniper hero » Fri Jun 13, 2008 11:25 am

the copper won't break fast but the solder 50/50 lead/tin holds 200psi when proper soldered
soldering isn't very diffecult but look up how to do it exact
the copper tanks just have a quite good flow that's why they are effective although I recomend to go bigger
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Unread postAuthor: LikimysCrotchus5 » Fri Jun 13, 2008 11:27 am

Well i am not sure what the chamber is on that gun you mentioned but if its copper i guess you can solder it.

The pilot really depends on how light your piston is and how much volume there is. What you want is small volume and a light piston. If you have done this well enough, then you can pilot it via schrader. But what i would probably recommend is a 1/4inch ball valve. Although most people pilot copper with a small QEV, its not really needed, its just a nice touch.

But i dont know what gun size you are going with. So it would help.
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Unread postAuthor: iisthemuffin » Fri Jun 13, 2008 11:30 am

I was thinking either a half inch or inch but im not really sure
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Unread postAuthor: Gippeto » Fri Jun 13, 2008 1:46 pm

Most everything you will need to know about working with copper can be found here;

http://www.copper.org/publications/pub_ ... ndbook.pdf
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Unread postAuthor: iisthemuffin » Fri Jun 13, 2008 2:19 pm

Thank you Gipetto. Ive downloaded and am reading now
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Unread postAuthor: Biopyro » Fri Jun 13, 2008 4:25 pm

Properly soldered copper will hold WELL over 200psi! I've taken mine to 300, and I reckon you'd be fine up to 1.5k.
I wouldn't be suprised if the pipe went before the soldered joints!
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Unread postAuthor: iisthemuffin » Fri Jun 13, 2008 4:31 pm

Wow thats actually quite surprising to me. Only problem i have now is not having the proper things to solder. Is it possible to build the cannon out of all threaded fittings? Is it possible to find the correct fittings to do this?


I read about someone using epoxy to connect copper in a piston cannon. They spoke of taking the cannon to 300psi. I dont think i trust this. But i have epoxy putty and it hardens very well. Feels like a solid rock when its done. It has steel in it. Would that be safe? Or will it just blow apart like im thinking it will?
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Unread postAuthor: DYI » Fri Jun 13, 2008 8:32 pm

Firstly, using epoxy would be more expensive, and weaker than proper solder (although still capable of holding well over a thousand psi if done properly).

Secondly, the solder you want is 95/5 tin antimony, NOT 50/50 lead/tin. If you use the proper solder, the joint's rating will be even higher than the rating of the tube.

Copper tube is made to a higher standard than pipes are, and has a higher safety factor included in its rating - almost 8 in some cases. It also has much better physical properties than almost any other material used in spudding; large temperature range, great ductility and shock resistance, and very favourable failure characteristics as a result.

Judging by the knowledge you've displayed here, I have a very good guess at why all of your piston cannons have failed. You need to get more familiar with the construction, materials, and design techniques before you'll have a design that works.
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Unread postAuthor: iisthemuffin » Fri Jun 13, 2008 10:07 pm

DYI, while you have given great advice and provided me with very good information i would just like to inform you that i have never built a piston cannon. Which means i have never built anything to fail in the first place. Im not trying to be rude. Its just a simple misunderstanding. I do tihnk i will be able to build a piston that operates correctly. Right now im just inquiring about connecting the copper.

Now that ive cleared that up. Your saying that the soldering equipment will be cheaper than epoxy? I mean this with no disrespect to you or your knowledge on the subject but i disagree. I can get a tube of epoxy putty that is about 8 inches long for 4 dollars. I think 2 of this tubes would be plenty for a 1/2 inch cannon. I could very well be wrong though. And i see you said if epoxied properly it will hold. Will you please clear up what you mean by properly? And just to put it out there, i wont be taking the cannon anywhere near 1000 psi. The compressor i have will only go to 300 so that will be my max for the moment.
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Unread postAuthor: kablooie » Sat Jun 14, 2008 1:31 am

I think DYI means in the long run, because while epoxy is cheap, you have to buy it every time you want to make a gun (unless you buy a huge amount, and that is not always practical, and will be very expensive). A propane torch, flux, and solder will last much longer, and will produce (IMO) better quality work. Also propane torches are really cool (yet quite hot at the same time).
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