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Hi CMac, When looking at buying a Tig unit you want the lowest possible amperage, usually 30amps is adaquote, as that allows for welding thinn metals. If your typical welding projects is welding 30ga or lighter then you would want a machine that would go 5amps. You can cheat here and use my homemade dropper resistor as explained below: To use that machine effectively then you need to use a dropper resistor made from a piece of 3/32" or 1/8" filler rod, depending on the amount of amps you want to drop. Attach the 1/8" filler rod to the welding bench with a vise-grip and let it hang vertical then attach the ground clamp to the other end of the filler rod. As the arc is established the filler rod (dropper resistor) will begin to heat thus lowering out-put amps at the torch. CAUTION as the filler rod can become cherry red dpending on the amount of amps being dropped. To adjust for the correct amount of amps required of the weldment, one could trim the filler rod to different lengths or change the diameter although I've never found this to be necessary. So with this little trick on a typical homeshop/industrail welding machine, 30amps would be adaquote for the low side. A fine infinite amperage control adjustment is a huge plus on a machine. On the high side you want about 120amps @ 60% to 100% duty cycle with most dry torchs as you can not stand the heat of the torch above 120amps for very long on your hand. Most dry torchs are rated too 150amps but at 150a or exceeding 150a will melt the torch in a very short time. If welding continously at high amps then you might want to consider a wet torch or water cooled. I've used a 500amp wet torch at 360amps welding a CU brew kettle and it was not fun even with multiple layered gloves and extra heat shields on my hood. On any welding process you can always make a multiple pass weld on thicker material so you want a machine that can do 150amps @ 60% duty cycle. This applies to most all welding applications. If the welding process is automated or in a production enviroment only then you would want a machine with a higher amperage and duty cycle rating. What welding process to use is determine by several considerations. I'll give a few examples: I spec'd a 6ft diameter valve to be welded at a Nuke plant with Tig (GTAW). What I was after is the most pure weldment possible with the least amount of possible mistakes, inclusions with-in the weldment. On a 4" steam pipe I would spec the root pass as Tig with the rest being SMAW (stick) welded. On 2" or less it would be Tig all the way. The root pass of any weldment is the most critical and any flaw here would most likely follow thru to the cover pass. I would spec Tig on a SS sink and counter top weld as I want the least amount of heat distrotion, be easy to finish the weld, obtain 100% penetration on a single pass weld. Stick/Mig welding here would surely distort the SS into a mess that was not usable. I would spec SMAW or GMAW (Mig) on a 3/16" plate where I want 100% root penetration in one pass with some inclusions with-in the weldment aceptable. Here joint type would be critical as were using 3/16" plate and have some concern about weld distortion in a single pass. Change that 3/8" plate and our concerns are much less as we could use a multiple pass weld, letting the plate cool between each pass. This should give you a good idea of why we spec different weld processes. I've only scratched the surface of this topic as it can get very in depth on all the considerations required. T_Bone
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