Enter the surface speed and the diameter you are cutting. You get spindle RPM, feed rate per minute and cycle time for the pass.
Inch or metric, starting speeds for common materials. Free, no sign-up.
Load a DXF or STEP drawing, pick your tools and conditions, and get G-code with nose radius compensation built in, then watch the cut in a 3D simulation before the spindle turns. Runs in the browser.
Surface speed is how fast the material moves past the cutting edge. For the same surface speed, a small diameter has to spin faster than a large one, so the spindle speed depends on the diameter being cut.
Example: 180 m/min on a 50 mm diameter → N = 180 × 1000 ÷ (3.1416 × 50) ≈ 1146 RPM. At 0.2 mm/rev that is F ≈ 229 mm/min, so a 100 mm pass takes about 26 seconds.
Example: 600 SFM on a 2 in diameter → N = 600 × 12 ÷ (3.1416 × 2) ≈ 1146 RPM. At 0.008 IPR that is about 9.2 IPM, so a 4 in pass takes about 26 seconds.
The "check" box shows the surface speed you actually get once the RPM is rounded to a whole number, which is what you would type into the control. On a CNC lathe running constant surface speed (G96), the control does this math for you at every diameter, so remember to clamp the maximum RPM with G50 (or G92) before facing toward center.
| Material | Roughing | Finishing |
|---|---|---|
| Carbon steel (1045 and similar) | 120–180 m/min 400–600 SFM | 180–250 m/min 600–820 SFM |
| Stainless (304) | 80–120 m/min 260–400 SFM | 120–180 m/min 400–600 SFM |
| Aluminum alloys | 200–500 m/min 650–1600 SFM | 300–800 m/min 1000–2600 SFM |
| Gray cast iron | 100–150 m/min 330–500 SFM | 150–220 m/min 500–720 SFM |
RPM = SFM × 12 ÷ (π × D), with D in inches. The shop shortcut is RPM = 3.82 × SFM ÷ D. For example, 600 SFM on a 2 inch diameter is about 1146 RPM.
RPM = Vc × 1000 ÷ (π × D), with Vc in m/min and D in mm. For example, 180 m/min on a 50 mm diameter is about 1146 RPM.
Use the diameter being cut, because surface speed is measured at the cutting edge. When facing or turning down a large step, the speed changes as the diameter changes, which is why CNC lathes use constant surface speed (G96) with a spindle clamp (G50 or G92).
IPR (inches per revolution) is how far the tool moves each time the part turns once, and it is what lathes are normally programmed in (G99). IPM (inches per minute) is IPR × RPM, the actual travel speed of the tool, which you need for cycle time.
No. They are typical starting points for coated carbide inserts. Adjust them to the insert maker's recommendation, the rigidity of the machine and setup, and how the chips and finish look.