Hardening a sprocket.


Active User
Feb 26, 2013
I need to make a sprocket. I have access to a Waterjet, mill, and lathe. I will cut it on the Waterjet. My problem is I need to harden it. I have mild steel, tool steel, hardox 450, stainless, and aluminum. Not sure how to treat it. We have a full weld shop for heating. Could open flame or we have the ceramic tempering machine for pipes. The sprocket is an obsolete sprocket for an old dirt bike.

Ulma Doctor

Infinitely Curious
H-M Supporter Gold Member
Feb 2, 2013
i can't wait to see how the Guru's are gonna answer this....:bitingnails:

what kinda bike we talking about??
if you say Bultaco i'm gonna loose it!!:lmao:

Ray C

Nov 16, 2012
If you specify the material and tell me what hardness level you want, I'll look-up the AISI specified recipe for heat treating and tempering it.

If I were making one myself, my standby material is 4140 or in general 41xx. Very nice stuff to work with, obtains a very nice level of hardness , hardens quite uniformly in the core and increases tensile strength as much a 2.5x as hardness goes up.

If it's going up against bicycle link chain, you'll probably want a hardness of around 55 or so.



Active User
May 4, 2013
Don't forget to taper the teeth of the sprocket before you harden it, or the taper will have to be ground. You can cut it on the lathe, or a grinder with a flap wheel while spinning, to avoid the interrupted cuts!

When I redneck harden something, the Weber grill comes out, and gets setup with an old hair dryer to burn hotter. I don't have a fancy oven like Ray, but I just eyeball it at a good orange color. Then a quick dunk in brine, or used motor oil, and rock on!

Be careful not to make the sprocket too hard, or the teeth will chip off! They tend to be harder than the rest of the sprocket, because they cool faster when quenched. You only need the sprocket to be slightly harder than the chain, which is generally not hardened.

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