The speed of your machine will depend on the size of your disk. Remember that diamonds like to run fast and, although you can run them slower, their efficiency will be greatly compromised by slower speeds.

Our recommendations for shaft speed are these:
If you are only grinding with your machine, stick to the high end of the scale, if you'll be grinding and polishing with your machine, go for the lower end. You won't see a lot of difference in the grinding efficiency, but you'll really need that lower speed when you go to use your polishing pad with your cerium.

The best of both worlds would be a variable speed machine that will accomodate both faster grinding and slower polishing.