How To: Drill a stack of metal sheets accurately

If you want accuracy, clamp 'em all on a mill bed, spot drill with a center drill, then follow through with first a 2mm drill, then the final size, using appropriate coolant. If you can tolerate a half millimeter of wander, you can do a 20mm stack in one go.

If you want convenience, dimple with a center punch and using that (by feel) locate the center spur of a (for instance) Whitney hand punch. Diameter with a punch is very repeatable, and the hole sides will be smooth and parallel.

Good advice, but I'll differ on one point. Use a spot drill to establish the hole start, then drill right to size in one shot. Me thinks this is more accurate. At least, that's the way I do it.

Karl

A drill bushing in a plate placed on top of the sheetmetal will give you the most accurate hole location. Also use a drill with short length flutes commonly used in aircraft sheetmetal work. You will be able to drill a number of sheets at once if you have a factory sharpened drill. You don't say how accurate you need the hole so you will just have to experiment on the number of sheets that will give you the accuracy you require.

John

Parabolic drill bits may give you better results.

jsw