Dan Phillips: Creative houses from reclaimed stuff.
Workshop - How to Make Popular Instructables - Offset 126. Spot Welder from a microwave oven transformer and water tank. I have seen a few projects which use an old microwave oven transformer re-wound with a low voltage secondary to make a hobby spot welder, and I decided to have a go at making one.
I ended up designing my own using copper sheet to make the secondary, following an unsatisfactory experience attempting to use wire I made from about 100 strands of stripped down CAT5 cable, which at nearly 6mm diameter wasn't thick enough and melted its insulation, causing the winding to short circuit. The copper strips were cut from an old domestic hot water tank, of the sort usually equipped with an immersion heater, though this one had a heat exchanger (which looks like it really needs to be made into a tesla coil primary... hmmmm....). The steel parts came mostly from an old rotary washing line which had lost it's line, and the electrodes were made from a brass arm from an old ball cock (still trying to think of something to make from the ball).