1. Tig welder
2. Shielding gas
3. Rod
4. Tungsten
Welder
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If your only going to weld stainless, a tig welder with DC will do.
But if your planning on welding aluminum, you need one that also does AC.
Try to get one that has a high frequency (HF) feature. It'll help with starting the arc, otherwise you have to stratch start it. You need high freq. to weld aluminum.
Some tig welders come with a air cooled tig torch and some are water cooled. The more expensive tig welders have a water cooling option.
Shielding gas
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Use argon as a shielding gas for tig welding.
Rod
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For welding stainless you want to use a rod thats eqivilant or stronger then whatever your welding.
Example: For 304SS use 308SS rod. For 321SS use 347SS rod.
Theres other rods for mild steel, aluminum, chromoly, etc...
Tungsten
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Use 2% thoriated tungsten. You can tell by the red marking on the tungsten.
Mig welding stainless
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Its possible to weld stainless using a mig welder, but you need a high powered mig welder (runs off 220V).
A 110V unit will do it, but you need to run a small wire (.023).
Use tri-mix (helium, argon, and co2) as a shielding gas.
Info about tig welding:
http://www.millerwelds.com/education/TIGhandbook
Tig welders:
http://www.millerwelds.com/products/tig
www.mylincolnelectric.com/Catalog/equipmentseries.asp?browse=101|207|
If your going to be tig welding pipe, look into this:
http://www.solarflux.com