Re: drilling SST?


"Brent Muller" <bmuller@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote in message
news:pan.2006.04.30.05.46.15.207122@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Tue, 25 Apr 2006 17:02:57 -0700, Harold and Susan Vordos wrote:

Keep the tool sharp, don't let it idle---and don't run too fast.
Stainless work hardens quickly----and what you described is exactly
that---work hardened.
<snip>

Harold
This is good advice. Learn what work-hardening is - some machinists think
it has something to do with heat-it does not.

Correct! You want a good example? Buck a stainless rivet, even one made
from 303 S, for a prolonged period of time, then check the hardness of the
head with a file. Make the file an old, useless one, for the teeth will
be instantly dulled where they contact the rivet head. Heat plays no role
in work hardening----although heat may be generated in the process, and
probably is.

I would only add that I
think a drill with a fat chisel point is the worst for this type of
stainless because chisel points work-harden the material. Use or make one
with a split point. When tapping, a high pressure lube like Moly-dee is
beneficial, IMHO. Brent.

Yep, that's right, too. The chisel point of a drill is extreme negative
rake, so it doesn't cut, it displaces. Cold working stainless is a quick
recipe for work hardening, and that's what you're doing when you drill with
a conventionally sharpened drill. A thinned web, or a split point is often
the solution to the problem of work hardening, but the toughness of
stainless is correspondingly hard on split points, so one must achieve a
delicate balance of cutting edge design to achieve longevity of cutting
tools and cut without hardening. Needless to say, a one-off project
wouldn't be as critical as a production run.

Harold




.

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