Speed, speed, speed!!! 600, 1500, 3000, 5000, or even 10000 RPMs? How many RPMs do we need to use? RPM stands for Revolutions Per Minute. Did you know that the optics industry uses FPM? This stands for Feet Per Minute. If you took a point on the outer edge of a rotating disk how many feet would it travel? If your disk was six inches and it was spinning at 1000 RPMs, that point would be traveling at 1571 FPM. What if your disk were 3 inches in diameter and also traveling at 1000 RPMs? Then a point at the outer edge would be traveling at 785 FPM. Half as fast! What if you were polishing glass with a half inch Dremel bob moving at 10000 RPMs? That would be 2618 FPM. This is ten times the RPMs of the six inch disk, but only 1047 FPM more. I think you get my point. FPM is a more accurate definition of the "speed" of a polishing disk. This is also the reason why I have chosen to use a ring/pad to polish glass. There is a much less variance of speed between the outer and inner edge of a pad that is only one inch or less wide. In fact there is less of a variance the larger the pad/ring. There is also less of a variance the thinner the ring. So a one half inch wide ring would have less of a variance of the FPM of the outer edge and inner edge, then the variance of the outer and inner edge of a one inch wide ring. This is important if the precise "speed" of the ring is critical to the performance of the polishing system. Most of the time it does.
Written by Henry Grover Jr.
henrygroverjr@gmail.com
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