Milling an induction hardened steel gear

[Skowinski]

I have a friend who has a simple project, taking about 100 thousandths off the thickness of a gear. But, it's listed as "induction hardened" with no Rockwell hardness value. I don't have any carbide insert tooling for my mill yet, and wondering if TiN coated end mills will likely work. If that's most likely a dead end we can go ahead and buy an insert end mill, but would like to use what I have if possible. Thanks for any advice.

 

[Lo-Fi]

The induction hardening is going to be for the teeth only, with the hardness fading as you get further into the center. You might have a chance with HSS if you go from the center out, removing the soft material under the hard stuff, but carbide is a better option regardless. Doesn't need to be insert, a carbide end mill mill will do.

Why mill rather than turn, though?

 

[benmychree]

Sounds like a job for a surface grinder; no other tooling is going to like the interrupted cut, and may cause chipping on the gear teeth.

 

[Skowinski]

Thanks, sounds like we should spring for a carbide end mill. I have a lathe, but not a lot of tooling and not sure how I would mount a gear to turn or get it square in the chuck. Just sounded easier to go at it with the milling machine? If we went with light passes would any potential chipping on the teeth be avoided?

 

[MrWhoopee]

Check the teeth with a file. Induction hardened gears are usually (though not always) made from a medium carbon steel (eg. 1045, 4140) that will only reach Rc 40-48 max. If the file cuts easily, that's what you have. If it slides right off, the teeth are in the Rc 60 range. If the file won't touch it, a HSS endmill is not recommended.