Here's a nifty tool designed to remove spot welds without destroying the panel you want to keep. I like to call it a Spot Weld Mill, because the cutter bit looks more like a flat nose milling cutter with a tiny center pilot tip. Position this tool over a spot welded flange, align the cutter with the weld spot, and pull the trigger. As it starts to turn the cutter moves forward trapping the flange between cutter and anvil with some force so you do not have to push hard to drill. The two-finger cutter guard and the C-frame anvil can be adjusted to control the depth of cut so it will cut through one layer of metal and stop without cutting the second layer.