Drill bit test results
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None of these four 3/8-in. bits dulled appreciably after drilling 160 holes
through oak, pine, MDF, aluminum and 3/16-in. mild steel. The primary difference
was in how true the holes were in the aluminum and how long each bit
lasted in the final torture test.
I headed into my highly sophisticated
drill analysis laboratory (my
garage) and scientifically tested four
types of 3/8-in. twist bits: a $2.75
high-speed steel bit, a $6 “black
oxide” bit, a $7 cobalt bit and a
$9.50 titanium bit. Using each bit
in a drill press, I drilled 75 holes in
pine, 40 holes in oak, 20 holes in
aluminum tubing, 20 holes in
medium-density fiberboard and
five holes in 3/16-in. mild steel.
All of them finished the test
without dulling appreciably.
The high-speed steel bit was a little
choppy on the last 20 holes in the
pine, and all the bits except the
titanium one tended to wander
and bore oversized holes in the
aluminum. But if you're a less-than-160-hole-drilling do-it-yourselfer,
working mainly in wood, you can
get by with any of them. As one
carpenter put it, “In my book it
doesn't really matter—I usually lose
them or snap them in two before
they have a chance to dull.”
To complete the test, I drilled
holes in the steel with each until
they dulled and became useless.
The score? The high-speed steel bit
was shot after 20 holes. The cobalt
and black oxide bits were still
boring after 25 additional holes, but
with substantial effort on my part.
The titanium bit just kept drilling
an endless line of perfect holes—my arm gave out before the bit did.
Note: A bit's composition isn't
the sole determinant in how well it
bores through metal. In general, bits
with “flatter” tips drill quicker, last
longer and have less “walk” than
those with “pointier” tips.