In article ,
Tim Killian wrote:

Not normally -- and even less if you have a set of split-point
drill bits. The primary purpose of the pilot drill is to eliminate
having to force the chisel tip of the drill bit (the blunt line at the
center) into the workpiece. When running a 1" drill bit into a
workpiece on a lathe or drill press, that chisel tip takes a lot of
force (and thus is more likely to bow the drill sideways and enlarge the
hole). If you make a pilot hole with a much smaller bit (just a little
smaller than the length of the chisel tip) the force needed goes way
down, and the job gets easier.

Of course, the same could be said for any size drill bit, but it
gets rather insane to pilot drill for a 0.100" diameter drill bit. :-)



Not insane at all. Pilot drills are usually fat and stubby so the point
won't wander. I've used a carbide pilot drill with a 1/8 shank and 1/32
tip to set up a close tolerance pattern of 3/32 holes.

We seem to have a confusion of terminology here. What you
appear to be talking about is the combined drill and countersink
intended to be used for making center holes for lathe turning between
centers. (And it is normally double-ended as well.)

If we drilled the
holes directly with a 3/32 bit (even a split point), there would be
differences of several thousandths when compared to the same pattern
that was pilot drilled first.

Hmm ... I would consider that application a "spotting" drill,
not a pilot drill. And there are spotting drills purpose made, which
have a center-cutting single-flute design with nothing much beyond the
single flute -- sort of like a single-flute countersink.

A pilot drill -- as I was using the term --and as I think the
original poster was using the term -- is a smaller drill bit used to
drill full depth clearance for the web to reduce the forces needed for
pushing the chisel point of the larger drill through the workpiece.

Enjoy,
DoN.
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