[swong46]

Hi all,

I have been doing light CNC and lots of manual machining work; mostly with HSS and some cobalt cutters. This is the first time I am machining hardened gears to reduce mass. I would like to do the gears on the CNC and purchased some solid carbide cutters. My plan is to mill a groove as wide as the tool about 0.3125" deep total, flip the gear and do the groove again, then do a circular bolt pattern through the web I created.

Question is what rpm and feed rate should I be going at for the milling and the plunging process? Or should I use my cobalt end mills instead? I have rough and finishing end mills.

Thanks!

[keebler303]

You will need to use carbide. Hopefully your machine is pretty beefy because you will need a lot of torque at very low speeds. Search for "machining hardened steel" for some example parameters. I don't have much experience with it myself.

Matt

[txcncman]

How hard? 36 Rockwell C?

[awerby]

to anneal the gears, machine them in their softened condition, then send them out for heat-treating after you're done to restore the hardness.

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[swong46]

Not sure what the hardness is but a fine file seems to just scratch the surface finish if that tells you anything.

I can have it tested on the Rockwell Tester next week.

[swong46]

After some researching, looks like they have a surface hardness of 58-60 HRC. That hardness is about 0.020-0.030" deep and below that would be 30-40 HRC.

My plan now is to get an indexable face grooving tool with carbide then do the bolt circle on the CNC

Now question is what speed on the lathe? I don't normally use carbide but understand I need a nice chip flow.

[txcncman]

Don't rule out grinding as a possible way to remove material.

[underthetire]

For stuff that hard, and if you have a rigid enough machine, I would look at ceramic compound tooling. I used to turn transmission input shafts that were not quite that hard, and they ate carbide up pretty fast.

[swong46]

Hmm ok, I'll check those out.
However let's say I try carbide, which do you think sounds more favorable for the carbide? Doing the BCD with c-drill and drill first and have interrupted turning or do the BCD after and have the carbide exposed to more hardened material?

[keebler303]

Uninterrupted is always better. Interrupted cuts beat the cutting edge repeatedly.

Matt