On Sat, 30 Aug 2003 08:30:30 +1200, Bruce Simpson
wrote:

I've found that, when drilling thin material such as 3mm, there's
little point (and sometimes a few problems) in drilling more than a
pilot (the size of the web in the final drill-bit) then the final
hole.

A lot depends on the hole size, and the rigidity of your drill press /
hand drill.

If you try to drill 13mm straight off with a hand drill, then there's
the potential for so a slight difference in cut depth from side to
side turning into a considerable off-axis force. The hole is likely to
wander like crazy, possibly with injury.

If you're drilling on a rigid drill press, then even then you can have
problems with thin sheet (and I mean 16 gauge) deforming beneath the
drill bit.

Personally I like to use a stepped drill or similar for this sort of
work (HVAC ?) You not only drill a pilot hole, you use it to guide
the next drill step.