I needed something to weld thin stainless steel together for my jet engine project, so came up with the following:
It uses a Larger than normal microwave oven transformer (courtesy of my late uncle who donated the defunct microwave to me when I was in my teens and it’s been in my it’ll-come-in-handy pile ever since) with the secondary removed and rewound with 2 1/2 turns of 70mm2 copper wire.
(More recent MOT in foreground for scale – still in my it’ll-come-in-handy pile. )
It seems very effective
That is two pieces of 0.5mm thick 304 stainless sheet – The numbers correspond to the timer settings on the knob (0 = 40mS, 1 = 50mS, 2 = 75mS 3 = 140mS )
Everything 1 and above tore a hole in the sheet when they were peeled apart (which is the test for a good spot weld).