Actually, the horizontal mill on which this attachment mounts has a 13-speed gear transmission which is fairly compact for the range it covers- it drives the table, but I'll never see another- the mill is near a century old and there aren't many others like it out there. What I intend to use is opposing cones with an idler wheel between them; it's a design that was used on some drillpresses long ago. Since the motor will be turning full speed all the time and won't run under load for long periods, I'd think it'll run cool enough. When I used it before the controller quit, it never seemed to get even warm. Usually, it's not loaded up all that much, but occasionally I need it to work pretty hard. Picture the head of a Bridgeport mill scaled down and you can envision what I'm doing. In fact, Bridgeport started in business making vertical attachments like this.
Rick A