"Pete & sheri" wrote in message
...
I am making a drilling/tapping block and I need to drill very straight
holes for 8 sizes of taps. I will be ok with the 1/4" and up, an maybe
even with the #10 tap. But I am looking for ideas on making the holes
for the #6 and #8 taps really straight. Any ideas? The holes will be
1" deep. I will make my prototype from mild steel, but later, I want to
make some from annealed 4140.
Actually, this tool will be used for both drilling and tapping, to
keep the tap drill straight and then to keep the tap straight. It
worked out quite well to just use the clearance drill of one size to be
the tap drill size of the next one, with a couple of minor adjustments.
So, I can cover both tap drills and clearance drills for 8 sizes (#6,
#8, #10, 1/4, 5/16. 3/8 and 1/2) with only 9 holes.

I would appreciate any ideas on making those small holes straight,
Pete Stanaitis


I have little to offer in the way of preventing drill drifting aside from
using a new undersized drill bit, followed by boring as far as possible,
then reaming to hopefully align the balance of the hole with the bored hole,
which should be dead straight. It's a tough call on small holes, though.

It's interesting to see your post, for there are those that seem to think
that twist drills automatically drill straight holes. I've had more than a
few people tell me they do, and more or less imply I'm crazy. One boldly
stated that he could drill through a foot of material and have his drill
come out on location. My experiences through the years prove I'm right,
though. Twist drills are very capable of drilling irregular and crooked
holes. You're wise to be concerned.

Harold