wrote:
As a rule of thumb, when working wood, use tools made for
woodworking. Duh!
Yes, mostly I do, but in this case, I'll use what works best! I found
the woood bit went a bit eccentric as it went through giving a slightly
tapered bore as it went through.



It's interesting to hear of your results on hole quality. I have
also found that a good, sharp HS twist drill works great in metal or
wood. I think the place where the special wood bits like the Forstner
( a fancy hole saw) are used is in drilling large holes. For 1/2" dia
holes or so and smaller, the twist drill is the way to go. If you need
a 2" or 3" hole or so, well a twist drill that size is a huge chunk of
metal, hard to find locally and expensive to boot. Hole saws do OK in
wood ( and even metal if you are carefull) up to 6" dia or so and are
what I use for large holes.

Regards,
Bud


People will always believe what they want to, but our government
actually spent a lot of time and money finding the answer to this one.
The whole reason the study I mentioned earlier was done was because they
found significant variations in their testing of bolted connections in
wood for aircraft. They found the proportional limit for a poorly
drilled hole may be as low as one-third of the allowable limit load from
the old ANC design manuals. In the joint study done by FPL and ANC for
aircraft structures, they compared the Forstner, Twist drill and machine
bit(what they are calling a machine bit looks to be what we would now
call a brad point with a center spur). The twist drill made a better
hole. From the report:

"In drilling the experimental holes to establish drilling technique,
the 120° (probably actually 118 0 ) twist drill appeared to produce the
smoothest hole. The 60° twist drill was about equally effective, but
offered no apparent advantages over the more common 120° drill. A hole
drilled with a machine bit with a slow spiral did not appear to differ
materially from one drilled with a machine bit with a fast spiral, or
from one drilled with a Foerstner bit."

and

"The machine bit and the Forstner bit had a tendency to produce
large chips which sometimes wedged underneath the horizontal cutting
edge. Some of the chips were complete washers in form, the full diameter
of the drill in size, up to 1/32 inch thick, and strong enough to remain
intact when the bit was withdrawn. In a few cases a chip became wedged
between the side of the bit and the wall of the hole and scored the wall."

Charles