The lathe as we know, is different than a mill in the simple fact that with a lathe, our part is what rotates and our tool is what stays steady.
Because of that we need to calculate our speed and feeds based of the rotation of the part.
Cutting Speed (SFPM) = (Spindle RPM X Cut Diameter (in.)) / 4
Like a mill we could use a G97 and set a constant speed of 500 and make our cut. But, what if we are preforming a cut that reduces the Cut Diameter parameter from above. (Think basic facing operation)
So we know that if we Decrease our cut diameter, we should technically increase our spindle speed. That is when we use the awesome block of g-code - G96.
The G96 command directs the controller to increase or decrese the sindle RPM by increments of 1 rpm (standard).
Directs the MCU to adjust the spindle RPM so that a surface speed of 600 SFPM is held constant during machining.