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


Well, I'd go the one poster one better. Go buy some drilling fixture
bushings, they're pretty cheap and readily available, when worn, you
don't have to chuck your block, just get a new bushing. You could
also make your own, drill your hole in an oversized piece of stock,
chuck between centers, turn outside to a slip fit in your block hole.
If you were really serious about it, you'd drill undersize, rough turn
the outside, harden and temper, chuck between centers, grind the
outside, chuck in a 4-jaw and grind the inside to size. Much easier
to buy the things, unless you're dead and your time isn't worth
anything.
Brownells sells a pretty nifty tapping block with removable bushings,
I've got one from way back, they're asking a lot more money these
days, though. Works great for round or flat work.


Stan