On 2/22/2011 13:20, Tim Wescott wrote:
Make a D-bit reamer, it's easy enough.
Yeah, just set the compound to 0.5 degree and turn one from drill rod.
They'll cut a little while without being hardened.

Surely you mean set the tailstock over?

Setting the tailstock over the few thous has the advantage of
simplicity. Run between centers. I assume moving the tailstock toward me
will reduce the tailstock end. Set for zero off the tailstock end, then
move the tailstock to me by .005 (roughly).

Get 6" of A-2 (cheap), face and center drill both ends, set up with dead
center/dog at headstock, live center at tailstock. Indicate so its
roughly parallel (what's a few thou between friends?), turn about 1/2
inch at tailstock to 9/16 (@.5625 dia) so it will pass through the small
end of the reamed section, then set the tailstock to me roughly .007 or
so, turn the taper over 1.000", then measure.

Still ditzing with the base size, initial impression is an .875 OD x
..500 ID by 1.000 inch long chunk of aluminum tubing. Drill out to 15mm
(just over .610). Then things get fuzzy. Check chuck concentricity. Set
tailstock back to dead on. Chuck up base, ream with D bit.

Tubing wall thickness is important. Lyman 93 center of aperture is .550
above bottom of clamp. I can get mounting blocks in various heights, up
to .500 high. Sight has to be @1.1" above bore, so .550 (sight) + .375
(base)+ .310 (to bore center) + .125 (7/8 OD thickness) is 1.081. I
think that is close enough.

Snap, no stock downstairs with a diameter that will work in steel that
will hold up. 16mm will be .639+. Use D bit like a tap, base in chuck,
spring loaded center in tailstock, D bit in tap chuck, ream to depth.