I hear you on this; I'm in the situation where neither my small shop nor my garage has 220-240V available. Also, I don't know if my current service will allow for another such circuit - in any case, I'd have to likely add an auxiliary panel to accommodate the extra breaker(s) needed, as my main panel is full.

But I do have one possibility - and maybe you do, too?

From the door to my garage that leads into the house, the laundry room is just around the corner. In that room, I have both the dryer and water heater, on separate circuits. So in theory, I have the voltage needed.

Now, the water heater is hard-wired, so nothing I can really do there (well, I could - but I won't). The dryer, on the other hand, is plugged into a 220V outlet (as they usually are).

So - what I have considered doing is making an extension cord; one with a plug for the dryer, and on the other end a socket for the welder. In case you aren't aware, the plug on a welder for 220VAC is different than the plug on a dryer. And technically, you're not supposed to use a welder on such a socket (there's something in the code that forbids it).

But people have been making and using such extension cords for almost the entire time such welders have been available, and I have not heard of any reasons against them. You can even purchase such cords thru some places, so they're even legal to sell, purchase, and own. It may be something having to do with the strain a welder puts on the plug and extension; that the extra connection can heat up too much?

Anyhow, maybe you could do something like this; get an IR thermometer and monitor the temperature of parts as you weld and use the circuit; see if there is any issues in that regard.

Another thing I've thought about doing, since the wall where the socket for the dryer is shared with the garage, is mounting a junction box, bringing in the 220, then tapping off it inside the junction box to a new socket and the old dryer socket. Then I could plug right into the socket in the garage without needing a custom "extension cord", so long as I unplug the dryer (maybe add a cover to both as well that can be locked to prevent both being used at the same time).

Something tells me, though, that such a setup would not be up to code - but I don't know for certain.

If you’re using an adapter to plug a high-current device into a low-current socket, there is a risk of fire from putting too much current through the in-wall wiring. Tripping a circuit breaker is more likely, though.

See https://en.m.wikipedia.org/wiki/NEMA_connector for lots of detail.

You can get in trouble if the welder expects a safety ground or neutral intended to carry current that you don't have (neither is safe substitute for the other). You can get in trouble if you connect the welder to a circuit that can deliver more current than it's designed for and something fails (it was designed to fail safely assuming that the circuit is limited to X amps by a fuse or breaker).

If the dryer outlet has all the wires the welder wants (and some extra) and the same current rating, an adapter that connects the desired wires and ignore the rest should be safe as long as it's made from big enough wire.