ONMY CNC Machining Tools
Turning Speed, Feed & Machining Time Calculator
Calculate cutting speed (vc), feed per revolution (fn), and cutting time (Tc) for CNC turning. Choose metric or imperial units, enter the values you know, and get results instantly.
Machining Parameters
Each result uses only its required inputs. You can calculate cutting speed, feed per revolution, or machining time independently.
Enter positive values or load an example.
Calculation Results
Theoretical constant-RPM cutting time only. Tool changes, rapid moves, machine acceleration, handling, and other non-cutting time are not included. For facing or constant-surface-speed turning, the changing cutting diameter/RPM must be considered separately.
Turning Speed and Feed Formulas
The formulas below apply to a steady spindle speed and a specified machined diameter. RPM remains the same in either unit system, while diameter, cutting speed, and feed units change.
| Parameter | Metric formula | Imperial formula |
|---|---|---|
| Cutting speed, vc | π × D(mm) × n / 1000 m/min | π × D(in) × n / 12 ft/min (SFM) |
| Feed per revolution, fn | vf / n mm/rev | vf / n in/rev (IPR) |
| Cutting time, Tc | L / vf minutes | L / vf minutes |
Here D = machined diameter, n = spindle speed (RPM), vf = linear feed rate, and L = machining travel length. Feed per revolution is also commonly called fn.
Worked Turning Calculation Example
Metric: D = 50 mm, n = 955 RPM, vf = 286.5 mm/min, L = 200 mm.
- Cutting speed: π × 50 × 955 / 1000 = 150.01 m/min.
- Feed per revolution: 286.5 / 955 = 0.3000 mm/rev.
- Cutting time: 200 / 286.5 = 0.698 min (about 41.9 seconds).
Imperial: D = 2 in, n = 940 RPM, vf = 11.27 in/min, L = 7.87 in.
- Cutting speed: π × 2 × 940 / 12 = 492.18 ft/min (SFM).
- Feed per revolution: 11.27 / 940 = 0.01199 in/rev.
- Cutting time: 7.87 / 11.27 = 0.698 min (about 41.9 seconds).
Frequently Asked Questions
What is the difference between cutting speed and spindle speed?
Cutting speed is the surface speed at the cutting diameter, expressed in m/min or ft/min (SFM). Spindle speed is the number of revolutions per minute (RPM). They are related by the machined diameter.
How do I calculate feed per revolution in turning?
Divide the linear feed rate by the spindle speed: fn = vf / n. For example, 286.5 mm/min divided by 955 RPM gives 0.3000 mm/rev.
Does this cutting time include tool changes and rapid moves?
No. The result represents theoretical cutting time for one constant-feed pass. It excludes setup, indexing, tool changes, non-cutting travel and other cycle-time allowances.
Can I use these formulas for CNC facing or G96 constant surface speed?
The simple time formula assumes constant feed per minute. During facing or G96 constant surface speed operation, the active cutting diameter and spindle RPM may change, so a more specific calculation is needed.
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Technical reference: Sandvik Coromant — Turning formulas and definitions. Example values illustrate calculations; they are not material-specific tooling recommendations.
