On Jun 17, 4:15*am, "DoN. Nichols" wrote:

* * * * He would have the habit of quenching because he *started*
machining back when high carbon steel was the common tool bit material
-- and quenching was *necessary* for those, or the tool would get hot
enough to anneal.

* * * * HSS changed things a lot -- but not for everyone. *And the
habits of quenching lasted a long time as people learned from other
older machinists.

* * * * Enjoy,
* * * * * * * * DoN.

When I grind tool bits, I will probably cool the HSS periodically.
Not because the HSS needs it, but because if I do not cool it, it
burns my hands. This may theoretically lead to microcracks. But
since I usually do some light grinding on the fine wheel after all the
heavy grinding, I figure the layer with any microcracks is ground off.
Sometimes I even polish the HSS using some fine sandpaper. At any
rate I have never observed any problems from keeping the HSS cool
enough to hold.

But do not accept or reject what I say without having tried it.
Theory is nice, but sometimes it just does not make a difference.
That is what I have found about polishing HSS tool bits. I read it is
suppose to provide longer tool life. But I am not convinced.
Certainly there is no dramatic difference in tool life that is
obvious.

Dan