Charles Vincent wrote in
t:



"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enough to remain intact when the bit was withdrawn.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."


Thanks, this is exactly what I discovered. It's good to know I'm going
down the correct path.


Couple of things I'm still uncertain of, though. The steel parts have
quite a tight fit on the bolts. Obviously any paint on the inside of
these holes is simply going to be forced out when I push a bolt through.
this is normal?
Also, there's a small ridge formed on the edge of each hole. I figure
it's OK to leave the excess material there for a couple of reasons, one,
it provides more material for the bolt to rest against, and two it
won'ts interfere with tightening the bolts down since there will only be
a washer up against the hole anyway.
If it is poor practice to leave the ridge on the edge, what's the best
method for getting rid of it? Aside from a special machien, I thought of
carefully cutting it down with a large dril bit, but I'd be afraid of
doing some damage to the part.
Any suggestions?