The first job,
then, is to limit the speed of the drill you're using, whether
a hand drill or a drill press. If you're using a trigger controlled
hand drill, set it on the lowest possible speed range, and
then pay strong attention to the actual speed of the drill
Hand drills can't
be as tightly speed regulated as can drill presses, so constant
attention to their speed is essential: in fact, though, it's
really best not to run Forstner bits in handheld drills, because
of the lack of speed control (and accuracy--Forstner bits
are made for clean, neat, accurate holes, which is seldom
what a handheld drill produces, regardless of bit type). The
list below shows the safe running speeds of different sized
Forstner bits, with the smaller sizes able to run at pretty
much the same speeds as twist drills, while the larger sizes--at
the top of the lists--must move more slowly.
An important step
in the interest of keeping your Forstner bits sharp and in
good shape is cleaning the hole bore often. Forstner bits
do not have flutes that can pass chips up and out to the surface
of the piece being drilled, so it's necessary to lift the
bit out of the bore, or almost out of the bore, every 15 to
Forstner bits with dull chippers (see fig. 1) feed poorly
and chips easily jam them up. When you get your Forstner bit,
it is almost ready to use. Honing the chipper faces will improve
their action immensely. You can use a straight or shaped stone,
Arkansas, Japanese or diamond, to get them perfectly smooth.
Hone only on the flat: you do not want to affect the edge
bevel at all.
When the rim (see
fig. 1) of your bit gets dull, sharpen it by using a 1000
grit stone, in a half-round or a slip stone style. Finish
by honing with a fine stone like a hard Arkansas or a 4000
grit water slip stone. When you are sharpening the inside
of the rim of a Forstner bit, never take off any more material
than necessary. Coarse scrape it until there's a clean edge.
Finish with your 4000 grit slipstone. When the chippers on
your Forstner bit get dull, sharpen them by stoning the face
of the throat and the bevel. Always stone exactly parallel
to the throat, to keep original angles. This means that you
must stone exactly parallel to the throat. Any sharpening
on a Forstner bit should be done in a way that maintains the
When your Forstner
bit comes from the factory, the chippers are about 0.005"
below the rim. Keep chippers slightly lower than the rim so
that the rim is severing the tips of any fibers before they
are removed by the chippers.
Use care to keep
original bevel angles all the way through any sharpening job.