Lathe machining time
How long a pass, a part and the whole batch take — from the length of cut, feed, RPM and number of passes, plus part handling time.
Quick answer
Pass time t = (L + approach) / F, feed per minute F = f × RPM. Example: 4″ cut + 0.1″ approach at 0.008 IPR and 1000 RPM → F = 8 IPM, t = 4.1 / 8 ≈ 0.51 min ≈ 31 s per pass. Metric: 102 mm at 0.2 mm/rev, 1000 RPM — the same 31 s.
Result
- Time per pass
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- Passes
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- Cutting time per part
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- Part including handling
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- Whole batch
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Only feed moves are counted. Rapids, tool changes and spindle ramp-up add another 10–30 % — time the first part for an accurate figure. Facing with G96 (constant surface speed) is faster than at constant RPM.
Who needs it and why
- Quoting — job cost is based on machine time: how many hours the batch takes.
- Lead time — when the order will be ready and how many shifts the machine is busy.
- Choosing cutting data — what a higher feed or depth of cut buys you: how much faster the batch goes.
- Comparing stock — bar closer to the finished size means fewer passes and less time.
The formula
t = (L + approach) / (f × n) × passes, where f is feed per revolution and n is RPM. For facing L is half the diameter difference. Passes from stock are stock per side divided by depth of cut, rounded up.
RPM and feed per minute from cutting speed are in the RPM calculator.