AC Motor Speed Control

Hi everyone,

I just purchased a used Rong Fu RF-30. I am starting to collect
tooling but the thing I would really like to change is the control of
the spindle speed. Moving belt postions to change spindle speed is a
pain in the rear.


Questions:
What is the best way to control the motor speed electrically?

Is there an inexpensive AC motor controller that can be added to
control the spindle speed or do I have to change to a different motor
type?

I want to do something that would be the next step in making the mill
CNC compatible.

Thanks in advance.