TAHA Engineering Toolsby TAHA Knowledge Lab

Machining & Workshop

Lathe Turning Time Calculator

Machining time for a turning operation from length, feed and RPM or cutting speed.

Inputs

Calculate from
A bar held in a lathe chuck with a cutting tool feeding along the length of cut L.nfeed f per revL
The tool moves along the work by feed f each revolution, so it travels at f × n. Time per pass = L ÷ (f × n), where L includes approach and overrun. Diagram not to scale.

Length the tool travels while feeding, including approach and overrun (often a few mm extra).

Result

Total cutting time
0.75
Time per pass
0.75
Feed rate (tool travel speed)
160
Working
Feed rate = 0.2 mm/rev × 800 rpm = 160 mm/min Time per pass = 120 mm ÷ 160 mm/min = 0.75 min Total = 0.75 × 1 = 0.75 min

The tool feeds at 160 mm/min, so each pass takes 0.75 min and all passes take 0.75 min of cutting time.

Educational estimate — check the assumptions below.

About this calculator

Turning time is the time the tool is actually cutting while it feeds along the workpiece. It is the starting point for estimating cycle times, machine loading and the cost of a turned part. The tool moves along the work by one feed for every turn of the spindle, so the travel speed is feed × RPM, and the time is length ÷ travel speed. You can enter the spindle speed directly, or a cutting speed and diameter (the RPM is then calculated for you).

Formula

vf = f × n    t = (L ÷ vf) × i

n = 1000 × Vc ÷ (π × D)

f = feed per revolution (mm/rev), n = spindle speed (rpm), vf = feed rate (mm/min), L = length of cut including approach and overrun (mm), i = number of passes, t = cutting time (min), Vc = cutting speed (m/min), D = diameter (mm).

Worked example

A 120 mm long cut at 0.2 mm/rev and 800 rpm, in 3 passes:

  • Feed rate = 0.2 × 800 = 160 mm/min
  • Time per pass = 120 ÷ 160 = 0.75 min (45 s)
  • Total = 0.75 × 3 = 2.25 min

From cutting speed: 150 m/min on a 60 mm diameter gives n = 1000 × 150 ÷ (π × 60) = 795.8 rpm.

Assumptions and limitations

  • Cutting time only. Loading, tool changes, rapid moves, measuring and setting up are not included — add them for a full cycle time.
  • Constant spindle speed and feed. With constant surface speed (CSS) on a CNC lathe, or when facing towards the centre, the RPM changes along the cut and this simple formula does not apply directly.
  • The calculator does not recommend feeds or speeds; take them from your tooling supplier’s data.

References

  • Standard machining-time relation t = L ÷ (f × n) for turning.