"Jim Wilkins" wrote in message ...

"Ed Huntress" wrote in message
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"Jim Wilkins" wrote in message ...

In my limited experience D bits are tricky to sharpen ...

-jsw

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[Ed]

There are several configurations of drill bits and reamers that are called
"D-bits." It sounds like you're making the kind with a center point.
They're a b**ch to make, as you suggest. I've had much better luck with
the simpler kind that's flat on the end.

I learned to make these from the old English MAP hobbyist books, which
describe several types. This article from a 1967 issue of Popular Science
describes D-bits pretty well:

http://tinyurl.com/qdcnuoa

--
Ed Huntress

That version is easier to make than the ones in Lindsay's "Deep Hole
Drilling". I stop at the step where the lathe tailstock needs to be
aligned, since trade school apes misused the original spindle on my
lathe as an anvil horn. The dealer swapped it but the replacement is
loose, drill bits visibly jump up to the center of rotation when they
bite into the work.

Centering with one of these center drill collets instead of a drill
chuck helps a lot:
http://www.collistoolholder.com/cgi-..._9_TYP_Q_GRP_1

-jsw

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[Ed]

Yeah, that looks good. I have some similar tailstock collets that I
inherited in the pile of tooling junk that my uncle passed along. I've never
used them, though.

--
Ed Huntress