Constant surface speed control is an NC function that keeps the cutting speed (surface speed) constant even as the machined diameter changes.
It is standard on modern machines and helps stabilize surface quality and shorten machining time.
A Closer Look
Because cutting speed is given by π × diameter × rpm ÷ 1000, at a fixed spindle speed the cutting speed falls as the diameter gets smaller.
In facing especially, the diameter approaches zero as the tool moves from the outside toward the center, the cutting speed drops sharply, and the finish near the center deteriorates.
Constant surface speed control automatically varies the spindle speed with the changing diameter so that the cutting speed stays constant.
This yields a uniform finish regardless of where on the part is being cut, and stabilizes tool life.
Note that in facing, the spindle speed would climb excessively as the diameter nears zero, so a maximum spindle speed limit must be set.