Cutting data calculator for CNC milling machines
Calculate speed and feed for your CNC milling machine based on material, tool diameter and number of teeth. The output values are professional reference values for programming.
Schnittdaten berechnen
Select material, enter tool diameter and number of teeth, you will immediately get reference values for speed and feed.
Consider your machine (optional)
Speed and feed are then additionally limited to the series data (conservative: smallest model variant) or to your spindle.
Note: All values are non-binding reference figures from machining practice and serve as a starting point. Die optimalen Schnittdaten hängen von Maschine, Spindel, Werkzeugqualität, Auskraglänge, Aufspannung und Material-Charge ab. Beginnen Sie konservativ und tasten Sie sich heran. Eine Haftung für Werkzeugbruch, Maschinenschäden oder Bearbeitungsergebnisse wird nicht übernommen.
What the Cutting Data Calculator Computes
The calculator determines the two most important machining parameters in CNC milling from just a few inputs: the spindle speed (n in rpm) and the feed rate (vf in mm/min). You enter the material, the tool diameter and the number of flutes on your cutter; the calculator suggests a suitable cutting speed and outputs the machine values. This allows you to set the spindle speed and feed rate for your NC program or for manual operation.
The Formulas in Detail
The calculation is based on two interrelated formulas. First, the spindle speed is determined from the cutting speed and the tool diameter:
n = (vc × 1000) / (π × d) [rpm]
The feed rate is then derived from the feed per tooth, the number of flutes and the previously calculated spindle speed:
vf = fz × z × n [mm/min]
| Quantity | Meaning | Unit |
|---|---|---|
| vc | Cutting speed | m/min |
| d | Tool diameter | mm |
| fz | Feed per tooth | mm |
| z | Number of flutes | – |
| n | Spindle speed | rpm |
| vf | Feed rate | mm/min |
Guideline Values for Cutting Speed (Solid Carbide)
For solid carbide (VHM) cutters, the following guideline ranges for vc apply depending on the workpiece material:
| Material | vc [m/min] |
|---|---|
| Softwood | 300–600 |
| Hardwood | 250–500 |
| Aluminium | 150–350 |
| Plastic | 200–500 |
| Brass | 100–250 |
| Steel | 60–120 |
Calculating Cutting Speed — The Rule of Thumb
Anyone wanting to estimate the cutting speed without a calculator can use the simplified rule of thumb:
n ≈ (vc × 320) / d
Here, π ≈ 3.14 is rounded and the factor 1000/π is simplified to around 320 — sufficient for a rough mental estimate. For precise programming, you should use the calculator above or the exact formula n = (vc × 1000) / (π × d) — the rule of thumb deviates by around 0.5%, which is usually negligible for mental arithmetic but unnecessary for final verification.
Spindle Speed Table: Guideline Values by Tool Diameter
The table shows the spindle speed ranges (rpm) calculated from the cutting speeds for common cutter diameters with two-flute solid carbide cutters. Intermediate sizes and the appropriate feed rate are provided by the calculator at the top of the page.
| Material | Ø 4 mm | Ø 6 mm | Ø 10 mm |
|---|---|---|---|
| Softwood | 24,000 | 16,000–24,000 | 9,500–19,000 |
| Hardwood | 20,000–24,000 | 13,500–24,000 | 8,000–16,000 |
| Plastic (PMMA, POM) | 16,000–24,000 | 10,500–24,000 | 6,500–16,000 |
| Aluminium | 12,000–24,000 | 8,000–18,500 | 5,000–11,000 |
| Brass | 8,000–20,000 | 5,500–13,500 | 3,000–8,000 |
| Structural steel S235 | 5,000–9,500 | 3,000–6,500 | 2,000–4,000 |
Calculated guideline values, limited to a realistic spindle upper limit of 24,000 rpm. The actually suitable spindle speed also depends on the machine, clamping and depth of cut — use the calculator above for your exact tool combination.
What You Should Look Out For
- All outputs are guideline values. The optimal parameters depend on tool quality, spindle power, clamping and depth of cut.
- Start conservatively within the ranges and adjust once running is stable.
- Adapt the feed per tooth fz to the diameter and cutting edge material.
Further calculators can be found in our overview of CNC calculators. Background information on tool selection can be found in the BZT Knowledge Centre.
Frequently Asked Questions
How do I calculate the spindle speed when milling?
The spindle speed is derived from n = (vc × 1000) / (π × d). Here, vc is the cutting speed in m/min and d is the tool diameter in mm. The result n is obtained in rpm.
How is the feed rate calculated?
The feed rate is calculated using vf = fz × z × n. fz is the feed per tooth in mm, z is the number of flutes and n is the previously determined spindle speed. The result vf is obtained in mm/min.
Which cutting speed applies to which material?
For solid carbide cutters, the guideline values are: softwood 300–600, hardwood 250–500, aluminium 150–350, plastic 200–500, brass 100–250 and steel 60–120 m/min.
Are the calculated values binding?
No, these are guideline values. The actually suitable parameters depend on the tool, machine, clamping and machining situation and should be tested on your setup.
What is the rule of thumb for cutting speed?
For a quick mental estimate, n ≈ (vc × 320) / d applies — a simplified version of the exact formula n = (vc × 1000) / (π × d), in which the factor 1000/π (≈ 318.3) is rounded to 320. The deviation is around 0.5%. For actual programming, the calculator above is nevertheless recommended.
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