On Wednesday, November 23, 2016 at 6:03:56 PM UTC-5, Bob La Londe wrote:
I have a box of rust covered bits of square bar I got along with a small
lathe I bought a few years ago. There were some carbide tipped junk junk
bits in the box, but it mostly looked like keystock. I was poking thru the
box the other day looking for one of those pieces of carbide when I noticed
what looked like an actual HSS lathe bit (unground). It had the undercut on
each end that comes on a lot of lathe bits, so I walked it over to the belt
sander and knocked the rust off. A name appeared on the side of it. I
can't recognize the name, but a name appeared none the less. I went ahead
and ground one end to a nice conservative right hand tool and put it in the
HSS bits drawer for my big lathe. Worse comes to worse I'll smear the end
off, but it took some work to grind so I don't think so.

Anyway, after finding that piece I went thru the box again one peice at a
time looking to see if there were any more. Except for the carbide tipped
mystery metal there were no more obvious lathe bits. The rest all looked to
me like precut keystock to me. Slightly rounded edges and a squared off end
with slightly rounded edges. Out of curiosity I grabbed my spring punch and
hit several peices of it with the punch, and then I went and got that lathe
bit and hit it with the spring punch. They all got a very tiny divot or
punch mark, but the mark seemed to be the same size on all of it. So... is
is all this square stock just a different shape of blank HSS bit or is it
the keystock it looks like to me? If it is just keystock can it be ground
and used for lathe bits in a pinch or would it be not quite hard enough?

I am just curious. I've got a decent selection of insert tooling and a few
pieces of known good HSS ground for stuff I don't have inserts for.

Keystock usually is just plain carbon steel -- not very hard. Try it and see how it performs.

High speed steel is not only hard (typically 62 - 66 Rc), but it has a tempering temperature of around 1,000 deg. F. Sometimes a little more (M4, M42 and above). You can use it right up to the tempering temperature without permanently softening it. That's why it's called "high-speed." You can run the cutting speed up until it just barely glows red -- in a fairly dark room, at least.

If you have some hard steel that's not HSS, you can do some cutting with it at low speeds. If it's plain carbon, it ought to take 450 deg. F. That's what was used before we had HSS. My old friend at American Machinist used music wire for cutting tools on his Unimat. That's pretty hard, but it's plain carbon steel.

--
Ed Huntress