Work out turning time instantly with clear inputs, formula shown and shareable results.
On a lathe the carriage advances by the feed per revolution each turn, so feed rate is rpm times feed per revolution and time is length divided by that. Cutting speed is shown alongside because it falls as the diameter is reduced, so a constant rpm gives a slower cut on each successive pass.
Feed rate
IPM = rpm x feed per revolution
Turning time
T = length / IPM; SFM = pi x D x rpm / 12
IPM = rpm x feed per revolution. On a lathe the carriage advances by the feed per revolution each turn, so feed rate is rpm times feed per revolution and time is length divided by that.
The control raises rpm as the diameter shrinks to hold cutting speed constant, which keeps tool life and finish uniform from the outside of a facing cut to the centre.
This calculator takes 4 inputs: Length to turn, Workpiece diameter, Spindle speed, Feed per revolution. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.