Turning (lathe) RPM calculator
On a lathe the workpiece spins, so the spindle speed follows from the workpiece diameter — enter it with the material and feed per revolution for speed and feed rate.
Why the workpiece diameter sets the speed
Cutting speed is how fast material passes the tool tip. On a lathe that's the workpiece surface, so n = (Vc × 1000) / (π × Øworkpiece). It also means the correct rpm changes as you cut: turn a 40 mm bar down to 20 mm and the right speed doubles. CNC lathes automate this as constant surface speed (G96); on a manual lathe you step the speed up as the diameter shrinks.
Which tooling do the default speeds assume?
Carbide inserts — the everyday choice on modern lathes. For HSS tooling, use roughly a third to half of the carbide value: just edit the Vc field.
What feed per revolution should I use?
Roughing: 0.2–0.4 mm/rev. Finishing: 0.05–0.15 mm/rev, where the feed together with the insert's nose radius determines the surface finish. The default 0.2 is a reasonable general-purpose start.
Are these values safe to use directly?
They are starting values for stable setups. Interrupted cuts, long slender parts and parting off warrant slower speeds. Respect your machine's limits and the insert manufacturer's data.
Is my data sent anywhere?
No — this runs entirely in your browser with plain JavaScript. Nothing is uploaded.
