Definitions
The workpiece rotates at a certain number of revolutions per miunte (rpm). This provides a specific cutting speed (or surface feed), vc measured in feet/minute at the cutting edge.
Normally, cutting speed is set as a constant value, which leads to variations in rpm as the machined diameter changes.
The tool movement in directions X and Z is called feed rate (fn), or fnx/fnz [inch/rev]. When feeding towards center (fnx), the rpm will increase until it reaches the rpm limit of the machine spindle. When this limitation is passed, the cutting speed vc will decrease until it reaches 0 ft/min at the component
center.
The feed has a great influence on chip formation, chip breaking, and thickness, and also influences how chips form in the insert geometry. In sideways turning or profiling (fnz), the depth of the cut (ap) will also influence chip formation.
Feed (fn) and depth of cut (ap) have the largest effect on productivity.