Thread: Forstner Bits

In a recent thread
(http://www.woodworkforums.ubeaut.com...d.php?t=41662),
TerryB described a hand injury sustained by a chap using a Forstner bit
in a air tool. Dr. B wasn't the attending physician at the ER, so he
didn't have all the details of the incident. I'd guess, though, that
both the tool and the workpiece were hand-held, as well as running the
tool at high speed; a triple taboo combination in my book. There are some
follow-on posts with additional insights.

Here's an article on use of Forstner bits:
http://www.woodcraft.com/articles.aspx?articleid=380
Covers speeds, care, and sharpening.

Here's my additional 1.5 cents' worth, absent from the article:
In spite of the speed chart in the article, I've had best performance
by using the lowest speed available for all sizes.

Some folks are troubled by the little divot left by the pilot point.
They eliminate the divot by filing off the pilot point. This solves the
immediate problem, but is best applied to an extra bit. (See the
following paragraph.) Curiously, Benjamin Forstner's original design
(US patent no. 155,148; Sept. 22, 1874) didn't have the pilot point. In
fact, Forstner's objective was precisely to eliminate the gimlet point
used in augers of the prior art, which he achieved by letting the rim
guide the bit.

Forstner bits perform best in side grain. In end grain, extra care is
needed. The bottom chippers are essentially rotary chisels. Try cutting
across end grain with a hand chisel, and you'll appreciate what the bit
has to contend with. In many woods, aggressive drilling with a large
bit can be well nigh impossible, assuming you don't set the workpiece
on fire. Is there any solution to this dilemma? Yes, but it takes extra
time. Key is to drill successive pilot holes by sort of an inside-out
process: Drill a shallow hole with the largest bit to be used, only
deep enough to establish the circumference. With the next smaller bit,
drill another shallow hole, using the previous bit's divot for
centering, again only deep enough to establish its circumference.
Repeat until you reach a smaller bit size capable of drilling the full
depth of the desired hole. Now, with the next larger bit, drill to full
depth; the bit is guided by the circumference established by its use on
the way in, but the cutting is done only with the saw-teeth on the rim,
and the chipper doesn't have to work across the grain. Repeat until you
reach the original large size bit. In many woods, you may be able to
skip a size step and put a small portion of the chipper to work. Quite
tedious, but may be more accurate than using a boring bar on your
lathe; and if you aren't using a lathe,

I'd suggest avoiding most uses of Forstner bits in a hand-held drill.
The article above cites difficulty with speed control. Another
difficulty is control of position and orientation. My only exceptions
would be with the added use of a guiding jig, such as used for round
hinge mortises ("European" hinges) or door locks.

Forstner bits can transmit enormous torque to the workpiece. Best to
use a drill press, and have it clamped to the table.

This is all I can think of at the moment. Please add your own insights,
recommendations, horror stories, etc. And (I guess) please try to keep
the drivel to less than about 50%.

Joe