In article t,
"Mike Rapoport" wrote:

When I dimple holes in thin sheet they get larger to the point where the
clecos won't hold. Should I drill holes that are to be dimpled for 1/8
rivets a little smaller (like #31 or #32)? What are others doing?

Mike
Murphy Moose.

Assuming you aren't overdimpling, which isn't a given, I'd check the
pre-dimpled hole size. I mean really check it, with a comparator if
possible, or a set of gauge pins at least. You're never going to get a
round hole with a drill bit, and it's common to get them oversized, as
well.

If dimpling adds to the hole diameter, you obviously don't want to start
with a hole that's already too big.

A drill chuck that runs out, a bent drill, or holding the drill at some
angle other than perpendicular to the workpiece will make an oversize
hole.

The closest approximation to a round, correctly sized hole, I believe,
is to punch it and then ream it. For newer Van's customers, the punching
is done. Throw out those silly drill bits and get a couple of reamers.