I'm making a couple of small gears in this horrible material and I can't seem to get it to behave.

I was able to get really tight, long pigtails when rough turning with the following:
Surface speed: 170 m/min
Depth: 0.5mm (radial)
Feed: 0.16mm/rev
Coated carbide insert (with a fancy chipbreaker) with 0.4mm corner radius

Couldn't get it to actually break the chips though.

Left .05mm for finish turning and that worked a treat with a ground and coated carbide insert; I forget the feed/speed, but I managed to get 0.37 um Ra surface finish which is fine.

Now I have to hob them and I'm stuck with HSS because we don't have a 2 Module carbide hob . Also, they specify N4 surface finish (0.2 um Ra) . The parts will be sent out for super-finishing to get there, but I still need to get it pretty good beforehand.

What I can find online is recommending about 7.5 m/min surface speed for milling, does that sound right? Because it puts me at 60 rpm on a 40mm hob, which seems awfully slow (the change gear chart also stops at 140rpm, so that's gonna be interesting... )

I suspect this is a prototyping/proof-of-concept exercise, so if it becomes an order for a few hundred we'd (better) get a carbide hob, but I still need to get these done and try to work out the best way to machine this stuff.

Anyone got ideas?


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