On 2009-10-03, wrote:
On Oct 3, 2:17*am, "Michael Koblic" wrote:
What is the expected tolerance of drill bits? I have a set of fractional,
letter and number drills. No.12 to 15 (including 3/16") seem to produce the
same size hole.

Have you measured the diameter of the drill bits? I could not find
tolerances on drill sizes, but drill blanks are the nominal size plus
nothing minus .0003 inches for blanks up to half inch. I would
expect drills to have about the same tolerances.

Note that it matters where you measure, too. Drill bits taper
very slightly from the cutting end to the shank (to avoid binding in the
hole, I guess). Certainly don't trust a measurement of the shank to
give the size of the hole it will produce.

As has already been mentioned -- it all depends on how well it
has been sharpened. If the angles or lengths of the flutes are
different, the drill will run off-center, and cut with only one flute,
while pivoting on the "center" as defined by the sharpening, not the
center-line of the bit itself.

Enjoy,
DoN.

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