Lathe Turning Calculator
Enter the material, the diameter and the cut to get spindle speed, feed rate, removal rate, cutting time, power and the finish the nose radius will leave.
Spindle speed for this cutting speed at other diameters (constant surface speed)
| Diameter (mm) | Spindle speed (rpm) |
|---|
How it works
The spindle speed is n = 1 000 × Vc ÷ (π × D), the feed rate Vf = n × f, the removal rate MRR = Vc × f × ap in cm³/min, the cutting power P = ap × f × Vc × kc ÷ 60 000 in kW, the cutting time for one pass L ÷ Vf, and the theoretical roughness Ra = f² ÷ (32 × r). If the spindle speed limit is lower than the speed the formula asks for, the calculator uses the limit and shows the lower cutting speed. The ideas are explained on the Turning: Lathes and Operations page.
Worked example
A 40 mm aluminum bar cut at 250 m/min with 0.2 mm/rev and 2 mm depth: n = 1 989 rpm, feed rate 398 mm/min, removal rate 100 cm³/min and a cutting power of 1.17 kW. The same cut in mild steel at 120 m/min: n = 955 rpm, 191 mm/min, 48 cm³/min and 1.44 kW. With a 0.8 mm nose radius and a feed of 0.1 mm/rev, the theoretical roughness is 0.39 µm.
Things to know
These are starting values for a rigid lathe and a sharp carbide insert. A small hobby lathe cannot supply the power in the example: reduce the depth of cut and the feed until the power fits, and check against the motor rating.
The specific cutting force kc changes with the chip thickness (it rises as the chip gets thinner); the values here are typical round numbers.
The finish is the theoretical value from the tool geometry. The real roughness is usually rougher, because of vibration, tool wear, built-up edge and material.
On a lathe with constant surface speed, the spindle speed rises as the diameter falls: the table shows the speeds at smaller diameters. Always set a spindle speed limit.
Common questions
What cutting speed should I use?
Use the tool maker’s value for the insert grade and material. The presets are typical carbide values; HSS tools run at about a third of these speeds.
What feed per revolution should I use?
0.15–0.4 mm/rev for roughing and 0.05–0.15 mm/rev for finishing, and no more than about half the nose radius.
Why does the spindle speed limit change the result?
A lathe cannot turn faster than its limit. The calculator then uses the limit, which gives a lower cutting speed than you asked for.
Is the power result what my motor must supply?
It is the power at the cutting edge. The motor and drive must supply more, to cover losses; the calculator shows about 1.25 times the cutting power.
Sources
- Oberg, E. et al., Machinery’s Handbook, 31st ed., Industrial Press: turning speeds, feeds and power.
- Sandvik Coromant, Turning Handbook and Formulas and Definitions.
Last reviewed: October 22, 2026