Bob Engelhardt writes:

After trying a couple of piece=of-cake welds, I thought I'd push the
envelope and tried it on 2 pieces of 1/8" mild steel. It had to let
it cook a while, but it was a perfect weld, as far as I can tell (peel
test). I don't think that I need to try for anything thicker 8-)

http://home.comcast.net/~bobengelhardt/weld.jpg

Neat! I'd be curious to see the plans.