SpudFiles

hi i would like to know how safe it is to solder a copper cannon and how much pressure normal copper can take.

solder is not gunna be strong enough to take any pressure, it is used strictly for electrical work and isnt strong at all.

i think for copper u use a tekneek called sweating, its on the wiki

copper can take a fair bit i think.

soz 4 the spelling i cnt b bopthered

Julz, sweating uses a special solder for pipe, normally tin/antimony, tin/silver, or tin/lead or something like that. The solder you're thinking of is wire solder, which doesnt require flux.

copper can hold a lot like 400 psi. but not many valves are rated to that. im not sure what the joints would hold to...... probably like 300.

drac: oh, ok then. i thought sweating was just heating up the copper so it expands into the othe part or copper and they somehow just stay like that...
thanks for the info

thnxs guys so sweating is soldering with a special type of solder can you get this a a hardware store or not

any store that sells plumbing supplies should have tin/antimony tin/lead solder

would using epoxy resin (which ive read on this site can take up to 2000 psi (wtf?)) be ok, as long as the joints are tight and strong?

i wouldnt, some epoxies dont bond well to metal, soldering is easy once you get the hang of it, maneuvering the propane torch is a bit difficult at first, make sure you have some heat resistant gloves (i use welders gloves) as a precaution, i've almost grabbed a hot piece of copper as it was falling, just a reflex.

A search indicates that the shear strength of tin-lead solder is about 5400 PSI. Although we don't know for certain, the shear strength of epoxy may well be less than the tensile strength, which is written on the package.
Thus, assuming that you are using an epoxy which makes good bonds to metals, epoxy should be fine for roughly 1/2 to 1/3 of the rating of a soldered joint. Going on memory, that's about 150-100 PSI... in which case you'd be better off using PVC.

tnxs i am going to use solder because i found out that my uncle welded his own plumbing at his house so he knows how to silver solder and he has a blow torch and all the solder that i need.

he welded his own plumbing? well that must have cost a fortune for all the steel pipe, or did you mean he soldered all the copper pipe in his house, we did that too, besides some liquid hot solder splashing on my leg, it went well.

yeah yeah he soldered all the copper for his plumbing
and how much damage did that solder do to your leg
ouch

soldering the pipes is your best bet. Its not all that hard to do either, i would suggest practicing a few times before you do it to your cannon.
Technically, its almost the same thing as cementing PVC together. You flux the copper pipe before you solder like you use PVC solvent before you use cement. The trick is gettting the solder to "suck in between" the fitting and pipe. a little trick i use is to add a little flux to the hot solder once you think that the weld is complete. The flux adds to the capilary action of the solder, possibly showing you a spot you could have missed.

As a precaution i would pressure test the copper pipe with air before using it for combustion.

Testing it with air wouldn't be any safer than just using it strait up... test it when it's filled with water. That way, if it fails, it'll only go "pop" and spill water every where - instead of going "BANG" and blowing a copper endcap through your window.