[rbourge]

I just got the Mill Arbor for a Sherline Mill and need the know the spindle speeds for a 16DP 55mm HSS involute gear cutter set. The big machines run these cutters slowly, around 100 RPM but I don't think the little Sherline motor can generate enough torque at that slow of a speed. I have tried light cuts and higher speeds seem to cut better but I am afraid to damage the cutter with a long series of cuts until I have more information. I am cutting Delrin, 6061 Al and Brass.

[Fastest1]

feed per tooth?

[rbourge]

An FpT of ten thousands should work for Alu and Brass and given that the cutter is 2.17 inches dia then rpm = 12 / 3.1416 x cutting speed/2.17 should give a usable spindle speed should it not? (assuming a cutting speed of 600 for Alu and 350 for Brass)

[skrubol]

Your speeds seem a bit aggressive, I think I'd halve them to start if you can. If you're losing torque going that low, those speeds should work, but on the brass you may see the tools wearing faster.
10 thou per tooth seems very aggressive for a little machine like that. I guess there is a lot of chip thinning and not a lot of material being cut, but I'd think 2-4 thou per tooth would be a lot safer.
Are you climbing or conventional?

[rbourge]

Your speeds seem a bit aggressive, I think I'd halve them to start if you can. If you're losing torque going that low, those speeds should work, but on the brass you may see the tools wearing faster.
10 thou per tooth seems very aggressive for a little machine like that. I guess there is a lot of chip thinning and not a lot of material being cut, but I'd think 2-4 thou per tooth would be a lot safer.
Are you climbing or conventional?

Yes after reflecting on what you said I am definitely running to aggressively to try to compensate for lack of torque. It seems to do just fine with lower speed and feed and the chips look better. I use conventional direction milling. There is definitely not enough torque for climb milling at this low speeds with that big involuted bit. Thanks for the input