A strange naive welding question: turning MIG into TIG

There are times when I'd love to be able to use the awesome power of this thing to just heat up some big chunk metal to cherry red for bending or pounding. The "proper" way, of course, is to heat with a torch.

I have tried heating large pieces with a torch to no avail. It seems that after a certain size, you just cannot get enough heat into the piece.

But when I weld a large piece at high current, it gets a large red area in a hurry.

So I was thinking- there ought to be a way to turn off the gas, pull the wire back so it doesn't feed, and replace the tip with some sort of carbon or tungsten electrode. Basically turning it into a Tig welder.

I know, I know, tig welders have different electrical characteristics than mig (constant current?), but I don't care- I just want to draw an arc for heating purposes.

Why is this not feasible? I KNOW that this idea will be shot down, I just don't know what the reasons will be ;)

It seems to me that I just need a way to connect a carbon rod to my Mig torch without screwing anything up. Looks like a little engineering is in order here...

And Mark, your calcs are based on a 50 amp supply- my Millermatic will do 250 continuous (I think), so multiply your numbers * 5. I have short tanks, and I'd go through gas in a hurry to get that kind of heat.

input: 44 Amps @ 230 Volts, or, 50 Amps @ 200 Volts
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right from the Miller website. Check out the Dialarc 250 AC/DC stick machine.

But, if you have a small AC machine, you can heat the heck out of something without a carbon arc torch. I mean if that's all you really want to do. Put one of the carbons in the electrode holder and crank up the amps. Long arc the carbon just enough to create a general heat and prevent a localized arc from overheating a smaller area. Keep it moving.

AC current will place half the heat in the carbon and half the heat in the metal. DC- would heat more metal and make the carbon last longer but carbons are dirt cheap. We sell them for about 25 cents each. That shouldn't break the bank.
Steve

As for your original problem, let's work out the math:

Your MIG welder is probably limited to about 50 amps input at 230 volts, or 11,500 watts. 1 watt equals 3.38 btu/hr, so 11,500 watts is 38,870 btu/hr. At best, you'll get 50% of this heat to your work part, so you end up with about 20,000 btu/hr. This is equivalent to a small rosebud torch tip. Go buy the biggest torch tip that you can get. Just remember to tell the salesman how big your acetylene tank is; the bigger the tank, the bigger the torch you can use. (You don't want to draw down more than 1/7 of the tank's capacity per hour, lest the acetylene become "unstable".)