Spindle RPM, feed rate and cutting time for a turning pass — set material, workpiece diameter and feed per revolution.
Turning uses the same surface-speed formula as drilling and milling, based on the workpiece diameter rather than a tool diameter: RPM = (cutting speed × 1000) ÷ (π × workpiece diameter). Feed rate follows directly from RPM and the chosen feed per revolution: Feed rate (mm/min) = RPM × feed per rev, and cutting time for a single pass is simply the length of cut divided by that feed rate.
Because RPM depends on workpiece diameter, a constant RPM through a facing cut (working from the outside in towards centre) means surface speed keeps changing — many CNC lathes offer a constant surface speed (CSS) mode that automatically adjusts RPM as diameter changes to keep cutting conditions consistent. For thread cutting or heavier interrupted cuts, reduce feed and speed from these general-purpose defaults.