[EricH]

Depending on the lathe, I think you could weld with one. Of course, that would be totally abusing it... And the weld wouldn't hold real well unless you ramped up the force a lathe can exert--and I mean REALLY ramped it up--but in the land of theory, it might be possible.

Now, arc welding, yeah, I can agree with you on. (Friction Stir welding is the type a lathe might possibly be capable of.)