CNC machining
Milling, turning, 3- to 5-axis machining centres
Free calculator
Spindle speed and feed rate calculation
Milling or turning: enter the cutting speed Vc and the diameter to get the spindle speed N, then the feed rate Vf. A reverse mode works out Vc from N.
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- Formulas and tables shown
Spindle speed and feed rate calculator
Spindle speed N
2,653 rpm
Feed rate Vf
397.9 mm/min
N = 1 000 × Vc / (π × D)= 1 000 × 100 / (π × 12) = 2,653 rpm
Vf = fz × Z × N= 0.05 × 3 × 2,653 = 397.9 mm/min
Cutting speeds should be taken from the tool manufacturer’s data. Calculated with no intermediate rounding.
The calculation is done in your browser: the values you enter are neither sent nor saved.
Formulas and units
The calculator’s four formulas and the meaning of each symbol.
Spindle speed
N = 1 000 × Vc / (π × D)
Milling and turning
Feed in milling
Vf = fz × Z × N
Feed per tooth, number of teeth
Feed in turning
Vf = f × N
Feed per revolution
Reverse calculation
Vc = π × D × N / 1 000
Resulting cutting speed
| Symbol | Meaning | Unit |
|---|---|---|
| Vc | Cutting speed (at the tool edge) | m/min |
| N | Spindle speed | rpm |
| D | Diameter of the tool (milling) or of the workpiece (turning) | mm |
| fz | Feed per tooth (milling) | mm/tooth |
| Z | Number of teeth on the tool | no unit |
| f | Feed per revolution (turning) | mm/rev |
| Vf | Feed rate (tool travel per minute) | mm/min |
Cutting speeds should be taken from the tool manufacturer’s data: this page offers no table of Vc by material.
How to read the result
The cutting speed Vc, in metres per minute, is the speed at which the tool edge moves relative to the material. A machine, however, is not set in m/min but in spindle speed N, in revolutions per minute. The calculator does the conversion: N = 1,000 × Vc / (π × D). In milling, D is the tool diameter; in turning, it is the diameter of the workpiece at the point where the tool cuts.
Once N is known, the feed rate Vf (in mm/min) gives the tool travel per minute. In milling, Vf = fz × Z, where fz is the feed per tooth and Z the number of teeth, multiplied by N. In turning, Vf = f × N, where f is the feed per revolution. With the example values in the form, Vc = 100 m/min and a 12 mm cutter give N ≈ 2,653 rpm; with 3 teeth at 0.05 mm per tooth, Vf ≈ 398 mm/min.
The “Vc calculation” mode works the other way round: from N and D, it gives Vc = π × D × N / 1,000. It is used to check the cutting speed actually achieved on a machine with a limited spindle, or to compare a manually set spindle speed with the value recommended by the tool manufacturer.
Where to find Vc, fz and f
Cutting speeds should be taken from the tool manufacturer’s data: catalogue, product sheet for the cutter or insert, the manufacturer’s online calculation app. They depend on the material and its grade, its condition (annealed, hardened), the tool geometry and coating, the coolant, the rigidity of the machine and the tool life you are aiming for.
This tool deliberately offers no table of cutting speeds by material: a generic value would be too approximate to be useful, and could damage the tool as well as the part. The values pre-filled in the form are only worked examples.
Pitfalls to avoid
- The right diameter. In milling, this is the diameter of the tool at the point of cut. For a ball-nose cutter, a tapered cutter or a shallow depth of cut, the effective diameter is smaller than the nominal diameter: use the one given by the manufacturer.
- The diameter that changes in turning. In facing, the diameter decreases towards the centre: at constant spindle speed, Vc falls towards zero. CNC controls offer a constant cutting speed mode (G96) and a constant spindle speed mode (G97).
- The spindle limit. If N exceeds the machine’s maximum speed, cap N: the actual cutting speed is then lower (“Vc calculation” mode) and the feed rate must be recalculated.
- fz and f are not interchangeable. fz is a feed per tooth (milling), f a feed per revolution (turning). In milling, the feed per revolution equals fz × Z. Only count in Z the teeth that actually cut.
- Manufacturer’s corrections. With a small radial engagement, the chip becomes thinner and manufacturers advise increasing fz. These corrections are not included here.
- Units. m/min for Vc, mm/min for Vf. In documentation using imperial units, Vc is expressed in surface feet per minute (SFM): 1 m/min ≈ 3.28 SFM.
In a drawing and in a request for quote
Cutting conditions do not appear on a drawing and are not the customer’s concern: they are part of the machining routing that the workshop builds around its machines and tools. Knowing them nonetheless helps you understand what drives the price of a part. The machining time of a pass follows from the feed rate: 200 mm travelled at 400 mm/min represents 30 seconds of cutting. Added to the other passes, tool changes and set-up, it makes up the cycle time, and therefore a large part of the price.
To get a good quote, do not try to impose cutting conditions: give the workshop what determines them, namely the material (grade and condition), tolerances, surface finish, quantity and the complete drawing. The guide on CNC machining prices details the items in a quote, and the roughness converter links the requested surface finish to finishing processes.
Frequently asked questions
A question not answered here? Visit the help centre or write to us.
How do I calculate the spindle speed for a milling cutter?
N (rpm) = 1,000 × Vc (m/min) / (π × D in mm). With Vc = 100 m/min and a 12 mm cutter, N ≈ 2,653 rpm. The cutting speed Vc should be taken from the tool manufacturer’s data.
How do I calculate the feed rate?
In milling, Vf = fz × Z × N; in turning, Vf = f × N. With N = 2,653 rpm, fz = 0.05 mm/tooth and Z = 3 teeth, Vf ≈ 398 mm/min. The feed per tooth or per revolution should also be read from the tool manufacturer’s data.
What cutting speed for aluminium, steel or stainless steel?
It depends on the tool, the grade, the condition of the material and the cutting conditions: there is no universal value. Consult the tool manufacturer’s catalogue or online app. This tool deliberately gives no values by material.
What is the difference between fz and f?
fz is the feed per tooth, used in milling, in mm/tooth. f is the feed per revolution, used in turning, in mm/rev. In milling, the feed per revolution equals fz × Z, where Z is the number of teeth that cut.
What if N exceeds my spindle’s maximum speed?
Limit N to the machine’s maximum speed: the actual cutting speed will be lower. You can calculate it with the “Vc calculation” mode (Vc = π × D × N / 1,000), then recalculate the feed rate with the new spindle speed.
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