Welding

[Eldarion]

I am starting work on my vacuum chamber and was just wondering, do you have to TiG weld everything, or will arc welding work too. I have an arc welder that I can use to construct every thing, but if TiG welding must be used, then I will find some one to do that for me instead.

[Carl Willis]

TIG welding is mandatory (at least according to the conventional wisdom) in high-vacuum construction. Generic arc welding with a handheld stick is great for making structural stuff, but the welds are porous, dirty, and completely unreliable in vacuum systems.

Off-topic now, let me make a suggestion: use your real name on these forums. It is just a suggestion, but most people do it because it makes their contributions look serious and credible.

-Carl

[Eldarion]

So what your saying is that the generic arc welding creates cracks an impurities so that a vacuum cannot be formed? If so then I will find someone qualified to do TiG welding and build the camber that way.

I also took your advice and changed my username.

[Doug Coulter]

I tig weld when it's the obvious thing to do -- some metals, including stainless steel, respond best to TIG, and have troubles with oxidation or other problems with any unshielded arc.

I have also found that in many cases a silver solder alloy will do pretty well, but it isn't as strong and you have to design the joint better. If you try this, make sure to get a solder alloy that contains nickel and no cadmium or other high vapor pressure components. There are special alloys designed for this, I get mine at McMaster-Carr.

The real troubles you get into welding on vacuum systems have to do with warping the work, which can ruin flanges to say the least, so TIG is still the king for most things, partly because it can be done very quickly without a lot of excess heat spreading. I always practice a little on a dummy piece so I have the motions smooth again before doing the real work on expensive parts, and everything adjusted perfectly.

[Eldarion]

Thanks for advice, is there anything else to keep in mind while building the vacuum chamber?

[Richard Hull]

Carl and Doug's admonitions are sage. In addition, design and layout are crucial as well as "measure twice, cut once". You can't undo welds! You can screw up in any number of ways, such that you build yourself into an unworkable situation with placement of components on the sphere or shell.

Make sure that the finished piece has no issues with hose or gauge fouling in the final mechanical installation and operation. I fashioned fake ports out of cardboard and taped them onto a sphere so that I could handle the piece and muse over altering their position to enhance access, mechanical mounting, servicabilty and pleasing visual presentation.

Good luck.

Richard Hull