On 4 Jan 2004 14:44:26 -0800, (Dan Caster) wrote:
My question was a lot more specific than how high is up. From the
various answers others have given it looks as if somewhere about .004
or .005 is reasonable for a drilled hole. Straighter than that and
one should plan on some other method of making the hole.

It appeared to me that most of the answers were really addressing
the question of how closely you could *locate* a twist drilled hole
rather than how straight a many drill diameter long bore would be.

The key factors for that are drill bit symmetry, material uniformity,
and whether you're recutting chips or not. Assuming a high quality
bit and a very uniform material with no inclusions or voids, the only
remaining issue is how to avoid recutting chips. For deep holes with
a twist drill, that requires a pecking technique, and the results of
that are highly variable from worker to worker.

I wouldn't be comfortable claiming a 0.004 to 0.005 variance for
*any* worker with *any* bit in *any* material, though a particular
worker might achieve it fairly routinely with a particular bit geometry
in a particular material.

There have been too many times when I've hit a hard spot in CRS,
or a void in cast iron, or a knot in a wooden plank, to issue a blanket
statement about how straight a deeply drilled hole will wind up being,
no matter how skilled the worker.

Gary