I have used a spotweld cutter before, but it dulled before I was half way done with a couple hundred spotwelds. I had an issue with getting the center to stay in the middle of the spotweld also.
I have been using a 3/16" drill bit since giving up on the spotweld cutter. The drill bit seemed to find the center of the spotwelds by itself. The 3/16" bit is plenty big to get all of the spotweld, and was just the right size to be able to get the bottom metal red hot for TIG welding the spotwelds back in. My old spotweld cutter made a huge hole, requiring too much welding, threatening warping of the panels.
