Thanks for the info, Bruce. I've got a couple more questions below if
you don't mind.

Bruce L. Bergman wrote:

You can use that 3-wire circuit, since there is no neutral load
(120V devices) in any welders I've seen. The neutral wire is bonded
to ground at the main panel, so for all practical purposes they're the
same thing - but they don't want you connecting any load returns (like
the dryer drum light or the oven light) to the safety ground.

That's what I thought; I just wanted to make sure I wasn't overlooking
some nuance of the neutral line concept that would end up wreaking
havoc on my welder (or me!).

Of
course, I'll need a plug adaptor -- I thought I'd use a 3-wire dryer
cord and connect the pigtails to an outlet matching the welder plug.

Will work fine - but make sure the breaker is rated to protect the
wires, don't change it out for a larger one. And if you crank the
welder up all the way and start laying big beads, you might trip it
out.

The welder specs say that max output for TIG mode requires a 208V/32A
or 230V/29A input circuit; for max stick output, the required input is
208V/40A or 230V/38A. My dryer circuit is 30A and I measured the
voltage to be about 240V. So, I don't expect any problems for TIG; for
stick, I'll have to stay below max to keep from tripping the breaker,
but I expect I'll be using TIG mode 90 % of the time anyway.

If the main panel is convenient to the garage and has some capacity
left, you can add your own 50A welder receptacle - unless you have an
oddball main panel like a Zinsco or ITE Pushmatic, it can be done for
under $50 in parts. Just use a short piece of flex conduit and put a
surface mount plug below the panel - or if the panel is on the outside
of the garage wall, use a nipple out the back of the panel can, and
surface mount a 4S box right behind it in the garage.

Adding a welder receptacle in the garage is what I would like to do,
but I'm not sure that's an (economical) option. The main panel has
only one empty breaker slot, but I assume I would need two slots for a
new 240V circuit, correct? That means I would have to add another
panel (at a cost considerably higher than $50), right? Or are there
other options? Could I for instance connect both the welder outlet and
the range outlet to the same 50A breaker (and still meet code)?

Bert