For cylindrical tool post grinding, the usual work speed range is 50 to 90 SFM. Generally speaking, a work speed of about 50 RPM seems to work well for most grinding operations. However, this speed can be varied to meet many grinding conditions.
If the wheel glazes (the grains dull before the bond wears), this means the wheel is too "hard" for conditions. A reasonable variation in apparent wheel grade can be compensated by varying the work speed. By increasing the workpiece RPM, the wheel will provide a "softer" action because it must now remove more material per wheel revolution. This increases the cutting force per grain, so the grains are more readily broken off, thus exposing new sharp grains and keeping the wheel from glazing.
Conversely, a wheel that is loading (bond wears before grain dulls) is too "soft" for conditions. This can be remedied to some degree by decreasing the work speed, so the wheel cuts less material per wheel revolution. As a result, the grains are less readily lost, making the wheel appear harder.
External grinding is done with the work rotating in the same direction as the wheel. Internal grinding is done with the work rotating in the opposite direction. Both these conditions will result in the contact faces of the work and the wheel moving in opposite directions, thus maximizing cutting action.