Chuck:
Sorry if I skipped a few definitions. TIG is Tungston Inert Gas more commonly known as Heliarc (TM) . It is not wire feed, and uses a "Torch" that has an electrode in the center of the tip, surrouded by a ceramic cup. A shielding gas, most commonly Argon or a CO2/Argon mix flows from the cup and shields the arc from the tip of the electrode to prevent rapid oxidation and contamination of the weld. You typically use uncoated welding rod with it and it's a lot like welding with an O/A (oxygen/acetylene)torch. It is not as forgiving of poor fit of the pieces to be welded, is slower and takes more time for setup. It also makes the prettiest welds with little or no cleanup. It is also what ya need if you are going to weld non-ferrous metals like aluminum.
MIG is actually known as GMAW (Gas Metal Arc Welding) and is what you know as wire feed. It's the "glue gun" of welding. Fast setup, fairly decent looking welds (depends on adjustments of the welder and how steady your hand is) and can be more forgiving of poor fit of parts. There are two basic types of MIG setups, one uses shielding gas, like TIG and the other uses a flux core wire, without the gas. The flux is a lot like the coating on the stick welding electrodes you used in High School and it required more cleanup - it tends to spatter quite a bit. The gas type requires a tank (like a welding tank), and a regulator/flow control. There are choices of gas, including straight CO2 (cheap, but leaves a dirtier weld and spatters more), but more often a 75%/25% Argon/CO2 mix, which leaves a clean weld, with good penetration.
There are a lot of good references on the net - Google "AWS" or just check this page out :
http://www.weldingengineer.com/
I don't do much of anything thicker than 1/4 inch plate for most of the stuff I fab - like motor mounts or some add on for the Cub or my Skag ZTR. I have recently been woking on some 3/8 plate for the "universal mounting bracket" I'm building for the back of the 129 and that took all 250 amps on my Linde TIG setup (very old equipment - early 70's, but still works good). Most everything I do now, I use my MIG, just because it's faster, but because I bought a smaller unit, 1/4 inch plate is pushing the limits . The hardest setup on the MIG welder is changing wire size for heavier or lighter projects and that only takes a few minutes to strip the old wire out,put the new wire and change the tip. Geez I rattle on - let me know if this helps.
KGI
(Message edited by kide on December 30, 2005)