Welding is an area where I know just enough to be dangerous! I do think unless you are starting with a wire feed an AC / DC machine would be much better than straight AC. If you do get an AC/DC I am thinking if you foresee some welding of much heavier steel such as building a car trailer or a log splitter, or anything involving the welding of thicker steel It might be a good idea to hang on to your AC/DC and later get a wire feed with perhaps a capacity of up to say 1/4" thick steel or thereabouts. This would mean you could buy a more modest priced wire feed machine that would cover your needs up to 1/4" thickness, but then for those times you would need the increased capacity you could fall back on your old AC/DC machine.
I think that is good logic, I have an old Lincoln Idealarc AC/DC 350 machine and I figured I could just buy a modest cost/sized machine that would cover 80% of anything I would ever need to do with the old Lincoln around for any really heavy needs.
So am I right here? If I want a wire feed that could weld a 1/2" or more it would cost considerably more to buy a machine that could handle the increased capacity wouldn't it?
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One way to look at the polarity issue is by the welding rods that are available to you. runs DC+ only. , which is similar to (forceful arc, deep penetration, light slag) runs best on AC, but runs all right DC+. runs best DC-, not good at all DC+. runs DC+ up to about 300 amps, better on AC above that. runs well either AC or DC+ for general welding, but was developed for high speed sheet metal work on DC-. And so forth.
The trouble with that approach is that it goes at the issue backward. What's important is matching the electrode (rod) to the job first, then running it on its best polarity after that. You would rarely match the polarity to the job first, and the rod to the polarity second---with two main exceptions: If you are having a problem with arc blow (the arc wanders off course because of the magnetic field caused by the location of the ground, or some other magnetic field disturbance) which you can't resolve by moving the ground clamp, you can turn to AC, which is not subject to arc blow. The other situation where polarity would be a primary consideration is when you know you need more of the heat in the work than in the rod. DC- provides 2/3 of the heat to the work, DC+ provides 2/3 of the heat to the electrode, and AC is 50/50. and electrodes were both originally developed for high speed sheet metal work on DC-, so that would be an example of a time to choose that polarity. I don't do much sheet metal work with stick, high speed or any other way, so I couldn't say. I do know that running DC- is unusually good at filling gaps in bad fitups, but is good for that too, and there's not as much slag to entrap with .
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DC is generally considered to strike an arc easier and stay lit better than AC, but if any electrode strikes easier or stays lit better than running AC (or DC, to be fair) I haven't run across it.
There are some real differences between the three polarities in stick welding, but they're not so profound that an inexperienced operator would even necessarily notice them. If your son gets to the point where he can tell just when to use one polarity rather than another, or even just how high to set the current, before he's burned ten thousand sticks, then he's got a real gift and maybe he should look into something that pays better.
All the best, Stan
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