BTW -- Don't use a twist drill when putting holes in sheet metal. Get yourself a couple of step drills... they're for sheet metal work.
Do you have a spot weld cutter? There are some real crappy versions out there -- and some good ones. Trust me -- the good ones are worth their weight in gold. Drilling out spot welds sucks. I use the Hougens roto broaches - they make a killer spot weld cutter. I center punch each weld real well - and then use my cutter... a good center punch keeps it from crawling offcenter.
http://www.hougen.com/cutters/sheetm...potweld_lg.jpg