The ideal Surface Feet Per Minute speed (SFPM) is between 3600 - 7500.
The formula for calculating SFPM is 0.25 x Diameter of Wheel x RPM.
So, a 4" wheel at 3000RPM gives a SFPM of 3000 (a little too slow)
A 6" wheel on the other hand gives a SFPM of 4500.
The higher the SFPM, the faster your polishing job will be done.
However, you have to remember that the larger and heavier the wheel is, the slower the drill will turn (reducing the RPM's).
If your drill has enough power to use 6" wheels without stopping the wheel if you apply moderate pressure, then by all means use the 6" wheels. Otherwise, step down to 4".
|