Estimating Lathe Cycle Time
Facing, OD turning, and parting-off all boil down to the same arithmetic: how far the tool has to travel, divided by how fast it moves. Feed rate in inches per revolution times spindle RPM gives the tool's actual linear feed rate in inches per minute, and dividing the travel distance by that feed rate gives the time for one pass. Multiply by the number of passes to get full operation time.
Why Facing and Parting Use Radius, Not Diameter
A facing or parting tool travels from the outside of the stock to the center (or close to it), which is a distance equal to the radius, not the full diameter. Turning along the length of a part, by contrast, covers the full length of cut. Mixing these up is one of the most common cycle-time estimating mistakes for new programmers.
What This Estimate Leaves Out
This calculator times only the cutting pass itself. Real cycle time also includes rapid traverse between passes, tool changes, spindle start/stop, and part handling, all of which add up across a production run even though each one is individually small.