On Dec 24, 9:08*am, Doug White wrote:
I need to drill a clearance hole for a #8 bolt (0.165" dia) through ~ 1
1/4" of 6061-T6 aluminum. *The first half is well inside the material,
but the last 3/4" needs to be close to one outside wall of the material.

I know that if I go too close to the wall, the material can give a
little, and the drill bit will drift towards the outside wall.
....
Another thought was to drill a smaller pilot hole that would be better
supported by the material, and then finish with the final clearance drill
which should follow the pilot hole.

The issue is deformation of the work when the (large) drill-tip
forces get near the sidewall. The 'pilot drill' technique seems
unlikely to work out well, unless you use a stepped drill (i.e.
a drill with a pilot section) to do the finish cut; after the
first hole is in, presumably straight (because it isn't close
to the wall), your second drill is ONLY guided by the sidewall
forces.

I'd try a short drill (for stiffness) from the thin side, and use
suitable lubricant. TiN bits in aluminum are somewhat self-
lubricating,
but you can't grind a standard one into a shortie. Finish with
a full-size twist drill, it clears chips better.