Just out of interest does anyone else use a 3 phase motor and an inverter to drive their mills or rollers.
A 3 phase motor can be picked up on ebay, often new, often for less than a tenner. Likewise an inverter for 30 - 40 quid.
This combination allows you to infinitely variably control the speed of rotation by easily varying the frequency from 0 - 200 % of 50 Hertz, with I believe, minimal loss of power.
I know that when mine is set to 18 Hz, the rpm is 95, which according to the passfire calculator is optimum for my jars.
I've recently bought a ridiculously large hobart dough mixing bowl to build a star roller, but I'm having a seriousl re think since seeing the great little one at the agm.
As Digger says, a pleasant half day tinkering about building your own which will be 100 times stronger than a gem polisher, is time well spent