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How Fast Should a Forstner Bit Spin?
Q:
I just bought a set of Forstner bits for my drill press.The first time I used one
I made more smoke than sawdust! How do I figure out the right spindle speed for
these bits?
A:
To find the fastest maximum speed for any size Forstner bit, do a little experimenting.
Start at a fairly slow speed (800 rpm for 1- to 1-3/8-in.bits, 600 rpm for larger
ones). If you make chips, fine. Bump up the speed one setting and try again. If you
make more sawdust than chips, you’re going too fast.
The right speed will vary with the density and moisture content of the wood.You
should be making long strings of chips rather than smoke or sawdust.Both smoke
and sawdust are warning signs that the bit is turning too fast or you’re pushing down
too hard.
So what’s wrong with a little smoke? If the bit turns too fast, it’ll overheat and turn
blue around the rim, indicating that it’s lost its temper (!). That’s not good. The bit
will dull much faster and won’t make a correctly sized hole.
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This story originally appeared in American Woodworker April 2002, issue #93.
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