Check your bearings for play. If they are babbitt and in good condition, you should be OK at 30 RPMs. A friend had a similar setup w/24" wheel. After I re-poured the bearings it ran fine at 30-35 RPMs. It worked great for sharpening axes.
BOLT IT TO THE FLOOR. It doesn't seem like it, given the weight, but they can be a bit top-heavy.