"Peter Divergilio" wrote in message
...
Drill bits?

D-bit drills are ground at an angle on the end, unless they're made to
follow a pre-drilled hole. D-bit reamers look almost the same but they're
usually pointed at the end, or tapered, like a clock reamer, or else they're
just left square on the end if they're just kissing the hole by a tenth or
two. The reamer design I've used a lot is ground to a long taper but all
from one side. They begin by cutting and finish by burnishing the hole.

They're interesting tools. You can even make milling cutters that way (the
old British hobby machining books covered them pretty thoroughly). I used to
make a lot of them out of broken and worn-out drill bits when I started
machining as a hobby, because my teacher started his machining in the 1920s
and thought everyone should know about D-bits first. I don't do much with
them anymore but they have saved me a lot of grief, not to mention money,
back when I was doing a lot of hobby work.

--
Ed Huntress