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.
Calculate cutting data
Select the material and enter tool diameter and number of flutes to get reference values for speed and feed straight away.
Consider your machine (optional)
Speed and feed are then additionally limited to the series data (conservative: smallest model variant) or to your spindle.
Reference values
Milling tools in the shop90 items
Note: All values are non-binding reference figures from machining practice and serve as a starting point. The optimum cutting data depend on machine, spindle, tool quality, overhang, clamping and material batch. Start conservatively. No liability is accepted for tool breakage, machine damage or machining results.
What the Cutting Data Calculator Calculates
From a few inputs, the calculator determines the two most important machining parameters in CNC milling: 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 of your milling cutter; the calculator suggests a suitable cutting speed and outputs the machine values. This lets you 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 related formulas. First, the spindle speed is determined from the cutting speed and the tool diameter:
n = (vc × 1000) / (π × d) [rpm]
The feed rate then results from the feed per tooth, the number of flutes and the spindle speed calculated beforehand:
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 milling cutters, the following guideline ranges apply to vc, 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 who wants to estimate the cutting speed without a calculator can use the simplified rule of thumb:
n ≈ (vc × 320) / d
Here π is rounded to 3.14 and the factor 1000/π is simplified to around 320. That is enough for a rough estimate in your head. 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 the final check.
Spindle Speed Table: Guideline Values by Tool Diameter
The table shows the spindle speed ranges (rpm) calculated from the cutting speeds for common milling cutter diameters, based on two-flute solid carbide milling cutters. Intermediate sizes and the matching 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 speed that is actually sensible 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 rather conservatively within the ranges and adjust once the machine is running stably.
- Adjust the feed per tooth fz to the diameter and the cutting material.
You will find further calculators in our overview of CNC calculators. Read background information on tool selection in the BZT Knowledge Centre.
Frequently Asked Questions
How do I calculate the spindle speed when milling?
The spindle speed results from n = (vc × 1000) / (π × d). Here, vc is the cutting speed in m/min and d is the tool diameter in mm. You obtain the result n in rpm.
How is the feed rate calculated?
The feed rate is calculated with vf = fz × z × n. fz is the feed per tooth in mm, z is the number of flutes and n is the spindle speed determined beforehand. The result vf is given in mm/min.
Which cutting speed applies to which material?
For solid carbide milling 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, they are guideline values. The parameters that are actually suitable depend on the tool, machine, clamping and machining situation, and should be tested on your own setup.
What is the rule of thumb for cutting speed?
For a quick estimate in your head, n ≈ (vc × 320) / d applies. This is 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 still recommended.
More CNC calculators
Looking for the right CNC gantry milling machine for your application? We are happy to advise you.