How to turn down gear hubs?

[Gui Cavalcanti]

If I were going to take the hub off, I'd clamp it in a vise with aluminum inserts ("soft" jaws) so as to not damage the teeth. I'd think this would only work if you have an even number of teeth, though; I think it'd get shaky with an odd number (clamping down on 3 instead of 4 teeth).

If I was going to take the diameter of the hub down, I'd do one of two things. If I wanted to do it absolutely right, I'd do what someone else suggested and mount a keyed shaft in the lathe and mount the sprocket/gear. If I wanted it done faster and cleaner I'd mount the gear to a rotary table and take off the hub with a milling machine, or mount it to a CNC's vise and say "give me a small circle here"