Banebot 56mm gearbox - double D related

[eugenebrooks]

Kevin is right about this. We have a heat treating furnace in our
shop that we have used to heat treat axles and shafts for several
seasons now. You soak the metal at a temperature above the transition
temperature to non-magnetic long enough for complete transformation
and then you quench, once, in oil or water as required by the material.
If you are not getting the metal above the temperature that ceases
to stick to a magnet, you are not doing much useful. We in fact use
a magnet on a soaked sample in the furnace to check that our
temperature meter is not off, we crank it up 25 degrees at a time
until the sample goes non-magnetic, and then give it another 50 degrees
for margin.

The shaft in the 56 mm transmission is already hardened. A high
speed steel cutter makes absolutely no progress on it. We learned
this when we attemped to turn a shaft into a square hole to mate to
a 4130 carrier plate that we made for a test of hardended material.
We ended up having to make a new shaft from 4130, and we will
heat treat the material tomorrow. If you heat the shaft from the
transmission you are likely to only temper it to a softer state.

Contrary to prior posts, water quench cools more quickly than oil
quench. Oil quench is dicated for some materials because water
cools too quickly and causes distortion. I would use oil for machined
parts that you do not want to risk distortion during quench. This part
is very thin. There is absolutely no need to water quench it. Oil will
cool it off quickly enough.

After a proper heat soak, and getting the part into the quench
before exposure to air cools the metal below the transition temperature
is really important, you have to temper. A temper at 800 degrees
is what we use on our axles. We do this in the furnace to get a
precise temperature, but they come out a dark blue and this is one
way you can tell what temper you have.

I don't know what the carrier plate in the bane bots tranny is made
of, so I don't know if it can be hardened. We made a carrier plate
and axle of 4130, with a square hole, and we will see what a proper
heat treatment of these parts gets us.

Eugene

Originally Posted by Kevin Sevcik

About hardening, I don't think the 3 times repeating will get you a lot of extra depth, but I'm going off my one class a couple years ago, same as Dr. Joe. If you're not heating it high enough to transform the metal and break your previous hardening, then your hardening isn't going to work. If you are heating it hot enough, then you're breaking down the previous hardening. I suspect what you might be doing is a poor man's version of carburizing, building up a layer of carbon from the volatilized motor oil, then letting it soak in by heating up the part again.

At any rate, some brief googling gives me a little better info for those trying the homebrew hardening. The austenizing point is apparently slightly past where the metal stops being magnetic. So heat a bit past where a magnet won't stick to it anymore. I'm also curious if the carrier can withstand a water quench if anyone has a carrier they wouldn't mind possibly warping or cracking.