On Mon, 06 May 2013 18:41:15 -0500, "Pete C."
wrote:


An upcoming project will have me making 8 different M1.25 spur gears to
replace missing change gears for a lathe that seem to be unavailable
from the manufacturer. I've got a set of gear cutters on the way from
China and I've been reading up on the machining process so I think I'm
good there. What I need to do is figure out the best steel to use so I
can order a chunk of bar from my steel supplier.

I don't have real heat treating capabilities yet, just your basic
Kasinit case hardening. The change gears in the lathe obviously don't
run 24x7 and don't carry huge loads generally so what steel would be
best and not overly difficult to machine? Is case hardening a good idea?
Presumably case hardening doesn't have as much warping potential as real
heat treating, and of course I don't have the capability of finish
grinding though I could perhaps rig up a fixture to run in the new gears
against each other with some lapping compound if that might help.

Thoughts? Suggestions?

There's more to it than this, but as a starting point, this is what I
was taught years ago by Gleason Works, who were world-class experts.

For quality machinery applications, the best gears are made from a
case-hardening grade and deep-case hardened. That's not Kasenit, but
an expert could do it with a compound like that. What Gleason was
talking about is case-hardening in a carbon-rich atmosphere, in a
furnace, for a long time: hours, usually, to produce a case that's
0.1" thick or more.

The next step down is flame-hardened gears. These are made from
high-carbon steel, or a quick-quenching high carbon alloy. This flame
hardening requires a fixture and a quenching system that surrounds the
gear all at once -- a spray-type or an agitated oil bath.

The next step down is through-hardened alloy gears.

The nest step is anything else. g There are lightly-loaded machinery
gears made of alloy or carbon steels that are half-hardened but still
machinable.

The idea is that you want the contact areas of the teeth to be very
hard for wear resistance, but the roots of the teeth have to tolerate
shocks in most applications.

Good luck! You'll probably get some grade-specific recommendations,
but this will give you an idea of where they fall.

--
Ed Huntress