On 26 Feb 2012 05:06:28 GMT, "DoN. Nichols"
wrote:

On 2012-02-25, Ed Huntress wrote:
On 25 Feb 2012 05:55:43 GMT, "DoN. Nichols"
wrote:

On 2012-02-24, Paul Drahn wrote:
On 2/23/2012 8:18 PM, Richard wrote:
On 2/23/2012 9:54 PM, Karl Townsend wrote:
I need to make a pin .25" long by .096" diameter with a 0.109 by 0.117
head. It needs to be hard so I'll make it out of a 7/64 drill bit, the
size of the head.

Note that most drill bits have a soft shank and a HSS blade, so
the shank won't do much for you. I don't think that it has enough
carbon to harden well at all. (If you only need the surface hardened,
you can get some Kasenite or other case hardening pack material for heat
treating it.

Don't case-harden HSS. The shank has plenty of carbon -- and chromium,
and probably molybdenum, to harden it up to over Rc 60.

Are you saying that the shank of a typical drill bit is also
HSS?

Yes.

I've always understood them to be mild steel welded to the HSS
which implements the flutes and other cutting surfaces.

I've never heard that. As far as I know, they just partially anneal
the shank, or maybe they don't quench the shank in the initial
heat-and-quench.


I was assuming that if he used the shank, and had to harden it,
it would be mild steel, not HSS, so I was not advising case-hardening
HSS.

However, it's not a good idea to do so. There are too many other
things going on with HSS alloys; you risk winding up with a weak part
unless you have good temperature control.

And it is likely that *if* the shank is really HSS, you won't be
able to machine it anyway, unless with a toolpost grinder. :-)

You can mill and turn annealed HSS. I've done it in my SB lathe, with
HSS lathe bits.

That is, assuming the shanks of HSS drill bits are HSS. g I'm pretty
sure they are, Don. I've never heard of them being welded. I would
think that would be an expensive way to make a dtill bit.

Before we leave this, we should point out that most grades of HSS have
*very* high carbon content -- 0.80% to 1.1%. That's up there in the
range of music wire and antique straight razors. You won't increase
hardenability by treating them with Kasenit. They already have all the
carbon they can use for hardening.

The problem with heat-treating HSS is that the alloy constituents that
form carbides (there are several) have to be heated just right or you
get variable results when they either 1) got back into solution or 2)
form free carbides. Without excellent temperature control and timing,
including temperature ramping and soaking, you get unknowable results,
with a strong possibility you will make the material brittle and weak.

So it's not a material to heat-and-quench with a torch, unless you're
willing to experiment.

--
Ed Huntress


Note that a heat-and-quench hardening will harden HSS, but it won't
make it "high-speed." HSS requires a two-stage heat treatment in order
to develop red hardness, and the second stage is a
solution/precipitation hardening that is a real challenge in a home
shop. It can be done, but you have to know what alloy you're dealing
with and you have to know just what you're doing. You also need *very*
good temperature control.

Not at all what I was advising.

Music wire or oil-hardening drill rod would be much preferred. They
can be easily and reliably hardened and tempered.

Agreed. Much better choices than old drill bit shanks.

Enjoy,
DoN.