Hi Tim,
Thanks. No, didn't use a punch, just used 25mm and 12mm twist drills for my 2mm sheet
More to the story of course. I drilled a 25mm hole and a 12mm hole in a piece of 8mm thick mild steel bar and then I clamped the 8mm bar, the 2mm alum. alloy sheet and a short length of hardwood decking (around 70mm x 12mm section) down onto the table of my pedestal drill. The holes in the steel bar served as the guide for the drill bits and the hardwood supplied something solid enough so that the drill wouldn't grab as it slowly drilled through the alloy sheet. I had also marked up the hole positions and drilled 6mm pilot holes, but even still, as it's just an ordinary drill press, each hole position required checking and rechecking a number of times to get it right.
Turned out quite well.
Cheers,
Glen