Pete & sheri wrote:

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.

Well, the obvious question is how straight do you need it? Are we talking
half a degree, an arc minute, an arc second? I would thing for tapping an
already existing hole in a part, that it makes no difference as long as the
tapping block is at least as straight as the drilled hole in the workpiece.
That is probably good to 10 arc minutes or so. If I needed to, I could
probably get it down to a few arc seconds, but most people don't have
the tools to measure angles to anywhere near that resolution.

Jon