Homemade Spot Welder. I had three MOTs (Microwave Oven Transformers) collecting dust in a box with a bunch of adapters and transformers.
The one was exceptional for the fact that the primary and secondary were separated by a shunt. Placed on it's base the secondary was on top and the primary on the bottom (pictured). I used a pipe cutting blade (hacksaw blade) on a reciprocating saw to cut the secondary off the transformer core. Near the end of the cut I had to use extreme caution as I did not want to damage the primary coil.