Harold and Susan Vordos wrote:
"Glenn" wrote in message
...
snnip------

If I had to make a twist drill into a piloted counter bore that is
how I would do it (and have done it).

Don't get me wrong. I've done it that way, too. Are there options?
You have a cutter grinder, a cylindrical grinder, or you use a tool
post grinder. Problem isn't in how the tool is generated, it's the
tool. There are better ways to deal with the issue-----which was my
point. If one is truly counterboring, not spot facing, the pilot is
trouble. Always has been, and likely to be in the future.

Counterbores tend to have short flutes that are restrictive in the
way of disposing of chips. They work fairly well for a spot face,
or a shallow counterbore, but when you start pecking, the fun begins.
Think of drilling with a 4 flute end mill and you come pretty close
to how a counterbore behaves, only you have to toss in the pilot/bore
problems.

Robin suggested that as long as long stringy chips are developed, you
have reasonable success. True, but when you interrupt the cut and
pull out, seems there's always that little chip that wants to find
its way to the bore and hang over the edge, assuring it gets bound up
with the pilot. When you're lucky, and maybe use an air hose
between cuts, you can eliminate most of the trouble, but it's faster
to change drills and use a tool that evacuates chips well and cuts
faster instead. I'll stick to my hand ground flat bottomed drills,
thanks.

Harold

T have never tried this (I will in the near future) but how about grinding a
flat (slightly less than the dfiameter - sort of like a 'D' bit) on the
pilot?
This should eliminate the 'chip' problem.

Ken.

--
Volunteer your idle computer time for cancer research
http//www.grid.org/download/gold/download.htm
Return address courtesy of Spammotel http://www.spammotel.com/