After a few nervous tests with some wood, I've decided that this motor just isn't a good choice. As you pointed out in the comments, vacuum motors are designed for high speed and low torque, which is just the opposite of what I need. I thought I could get away with it if I made a nice controller, but I changed my mind and set out in search of a better motor.

I was fortunate enough to get my hands on this very clean washing machine motor and accompanying circuitry.

But with this new gem that is designed for low speed and high torque I will make another attempt at a wood lathe. Unfortunately, since this is an AC brushless motor, I will have to completely redesign my driver circuit. I am planning to use the triacs from the washing machine along with some MOC3043 chips to drive them. I'm still doing my homework to figure out a good design since I've never driven AC motors before.

In addition to that, I will have to redesign the whole interface between the motor and wood. I salvaged the other pulley and belt as well, so I will probably make use of them. I'll post again when I have a working design.