Speeds & Feeds.
CNC milling calculator. Compute spindle RPM, feed rate, chip load per tooth, material removal rate (MRR), and required spindle horsepower from cutting parameters.
Vf (mm/min) = n × Z × fz
MRR (cm³/min) = ap × ae × Vf / 1000
P (kW) = MRR × Kc / 60000
Typical surface speed reference (Vc, m/min)
| Material | HSS | Carbide | Coated carbide | Typical fz (mm) |
|---|---|---|---|---|
| Aluminium 6061 / 7075 | 120–180 | 400–700 | 500–1000 | 0.05–0.15 |
| Brass / bronze | 60–90 | 150–300 | 200–400 | 0.05–0.12 |
| Cast iron — gray | 20–35 | 80–150 | 120–200 | 0.10–0.20 |
| Mild steel (1018, EN8) | 25–35 | 100–180 | 150–280 | 0.05–0.15 |
| Alloy steel (4140, EN24) | 15–25 | 80–120 | 120–200 | 0.05–0.12 |
| Stainless 304 | 15–25 | 60–100 | 100–180 | 0.04–0.10 |
| Stainless 316 | 12–20 | 50–90 | 80–150 | 0.04–0.10 |
| Titanium Ti-6Al-4V | 8–15 | 30–60 | 50–100 | 0.03–0.08 |
Speeds and Feeds for CNC Machining
Speeds and feeds are the cutting parameters that govern tool life, surface finish, dimensional accuracy, and machining time. Get them right and parts come off the machine clean and to size; get them wrong and you scrap parts, break tools, and trash spindle bearings.
Core Formulas
RPM = (1000 × Vc) / (π × D)
Feed rate (mm/min) = RPM × Z × fz
MRR (cm³/min) = ap × ae × Feed / 1000
Cutting power (kW) = MRR × Kc / 60000
Where Vc = cutting speed (m/min), D = tool diameter (mm), Z = number of flutes, fz = feed per tooth (mm), ap = axial depth of cut, ae = radial depth of cut, Kc = specific cutting force (N/mm²).
Typical Cutting Speeds (Vc) by Material
- Aluminum 6061 — 300-600 m/min (carbide), 100-200 m/min (HSS)
- Mild steel C1018 — 100-180 m/min (carbide)
- Stainless 304 — 60-90 m/min (carbide)
- Titanium Ti-6Al-4V — 30-60 m/min (carbide, with coolant)
- Tool steel D2 hardened — 25-50 m/min (CBN preferred)
- Brass / Bronze — 200-400 m/min
Worked Example
10 mm 4-flute carbide endmill, mild steel, Vc = 150 m/min, fz = 0.04 mm/tooth, ap = 5 mm, ae = 3 mm.
- RPM = (1000 × 150) / (π × 10) = 4,775 RPM
- Feed = 4,775 × 4 × 0.04 = 764 mm/min
- MRR = 5 × 3 × 764 / 1000 = 11.5 cm³/min
- Power (with Kc ≈ 2400 N/mm² for mild steel) = 11.5 × 2400 / 60000 = 0.46 kW
Common Speed/Feed Mistakes
- Using HSS speeds for carbide — carbide runs 3-5× faster. Slow carbide rubs and dulls quickly.
- Ignoring chipload (fz) — too low causes tool rubbing and work-hardening; too high causes tool breakage.
- Forgetting coolant in difficult materials — titanium and stainless need flood coolant or MQL.
- Not adjusting for radial engagement — high-speed machining (HSM) uses light radial (~10% D) at higher feeds.
Related Tools
Combine speeds/feeds with Cycle Time Calculator for full part costing. Track production efficiency with OEE Calculator. For surface finish prediction, see Surface Finish. To estimate ROI on faster machining, see CadNexa ROI.