When I started grinding razors my friends grinder ran at 1750 rpm and drove a 10" drive wheel. That computes to

10" x 3.146 (Pi) = 31.46 inches circumference of the drive wheel

31.46 x 1750 rpm = 55055 inches per minute

55055" / 12 " = 4587 surface feet per minute!

This was far to fast to do any hollow grinding.

So, now I have a different grinder that runs at 1750 rpm and drives a 4" drive wheel.

4 x 3.146 = 12.58" circumference

12.58 x 1750 rpm = 22022 inches per minute

22022" / 12" = 1835 surface feet per minute

This speed allows me to grind the hollows much better but I will be slowing it down even further as I get closer to the desired thickness.

Hope this helps,