DP2 #7 Invoulte gear cutter

kirk05 · Aug 10, 2021

This is my first time cutting a gear of this size. First attempt didn't go so well. Cutting 4140HT, sent it out and had the hardness taken out of it. Got a new cutter (because the first attempt completely dulled it and left flat spots on the cutter) and was wondering what the appropriate spindle rpm would be best to use. I've tried all speeds from 40rpm to 100rpm at .002 for my chip load. Even then was getting a bunch of vibration and nothing I seemed to do was helping. The cutter I'm using is 5-7/8" outside diameter with 10 teeth, just HSS. Any info would be very helpful!

Thanks TJ

HuFlungDung · Aug 10, 2021

I would rough (carefully) the tooth space with a slitting saw or a series of narrow side mills to nearly full depth. This eliminates a whole lot of the banging that goes on getting the tool to start in the cut. When most of the cutting is on each side of the cutter and not on the tips, it is a LOT smoother cutting. Because it is HSS, I'd go slower, rather than faster. 40 rpm is ok, or even slower if available.

Use a tailstock to support the work. Maybe even use a jack underneath the blank. You'd still need a beefy machine to make a go of it.

Dan from Oakland · Aug 10, 2021

40 RPM comes out to 60 ft/min cutter speed which should be ok for a 28-32Rc material. You don't say what you are running for coolant but you certainly can't run it dry. Ideal would be with a steady flow of cutting oil. Running coolant, you would want the mix to be pretty high concentration. 2 DP is going to require a very rigid setup- what machine are you running this on?? I might suggest that you rough out the tooth space with a regular milling cutter or even slot the blank with an end mill depending on your situation. That's a lot of material to remove using an involute cutter. One more question- what is your depth of cut per pass? Hope this helps.

Phil in Montana · Aug 10, 2021

rough as close as possible before using the form cutter. I use a .25 wheel cutter and than a radius wheel cutter moving side to side. Just keep a little for the form cutter to remove...Phil

kirk05 · Aug 10, 2021

Yes I cut out close to the tooth profile with a roughing endmill before I even tried to use the gear cutter. One end is in the chuck jaws of the 4th axis and the tailstock is also in the other end with a plate welded to it, and bolted down to the table, lol. When that didn't work I got 2 of the starrett jacks to put underneath a tooth on both sides. This is why I'm confused on the vibration. I'm using an Atrump cnc mill with a 5hp motor.

kirk05 · Aug 10, 2021

Sorry Dan, yes I'm using flood coolant while I'm running the cutter. I'm using rustlick cutting oil and for the cnc mills I double the recommend oil to water ratio. I'm using an Atrump cnc mill with a 5hp motor. Yes I also roughed out close to the profile of the tooth with a roughing endmill. With the roughing endmill I went 1" deep and opened the sidewalls on a 12° angle both ways since each tooth is spaced 24° apart. When I put in the cutter I went 0.8500" deep on my first pass. Which it was only taking about 0.0500-0.0600" on the top and bottom side. The small radius tip of the cutter wasn't even cutting anything yet. It helps I'm making sure that it isn't just me screwing up completely, lol.

EmGo · Aug 10, 2021

kirk05 said:
It helps I'm making sure that it isn't just me screwing up completely, lol.

Not just you. We used a 50,000 lb gasher to do that. You could probably get away with something wimpier but this isn't a Bridgeport kinda job ...

HuFlungDung · Aug 11, 2021

I'm not sure how your tooling is set up in a cnc mill to do this, but if the cutter is running on a stub arbor without an end support, I don't think you'd get it solid enough.
Another option to try would be laying the gear on a rotary table, and feeding up in Z to make the cuts. But I would attempt this on a horizontal mill with an overarm and an overarm support with a tiebar to the knee.

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