Joseph Gwinn fired this volley in news:joegwinn-
:


And, it does a bad job on the sheet metal. Solution is a Unibit.


Even a BFB of a drill bit will do a fine job if the spindle is rigid and
the work is rigidly mounted. It can't make anything but a round hole if
nothing moves.

Those epicyclic triangular holes you get are from relative motion between
the drill bit and the work.

LLoyd