⚙️ Machining
CNC Feed & Speed Calculator
Calculate feed rate, chipload and surface speed for a milling cut. Enter the spindle speed, cutter and tooth load, then press Calculate.
About the CNC Feed & Speed Calculator
Feed rate is how fast the cutter moves through the material, usually in mm/min. It is built from three numbers: spindle RPM, the number of cutting edges (flutes) and the chip load per tooth. Feed rate = RPM × flutes × chip load. If any one changes, the feed must change with it.
Surface speed (cutting speed) is the speed of the cutter's edge past the material, in metres per minute. It depends on diameter and RPM: SFM = π × diameter × RPM ÷ 1,000. Harder materials need lower surface speed; small cutters need higher RPM to reach the same surface speed.
How the calculation works
- Feed rate (mm/min) = RPM × flutes × chip load (mm/tooth).
- Surface speed (m/min) = π × diameter (mm) × RPM ÷ 1,000.
- Chip load = feed rate ÷ (RPM × flutes).
- Feed per revolution = feed rate ÷ RPM.
Reference values
| Material | Surface speed (m/min) | Chip load guide (mm) |
|---|---|---|
| Aluminium | 300–500 | 0.05–0.15 |
| Brass | 200–350 | 0.05–0.12 |
| Mild steel | 100–180 | 0.03–0.08 |
| Stainless steel | 60–120 | 0.02–0.05 |
| Hardwood | 300–600 | 0.10–0.25 |
| MDF / plywood | 400–700 | 0.10–0.30 |
Worked example: a 6 mm two-flute cutter
A 6 mm two-flute cutter at 18,000 RPM with a 0.05 mm chip load feeds at 18,000 × 2 × 0.05 = 1,800 mm/min. Surface speed is π × 6 × 18,000 ÷ 1,000 = 339 m/min, which is in the aluminium range. At 24,000 RPM the same chip load gives 2,400 mm/min.
If the feed is too slow, the cutter rubs instead of cutting, which generates heat and dulls the edge quickly. If it is too fast, the tool deflects and the finish suffers. Start conservatively, listen to the cut, and increase the feed until the chips look right for the material.