Spindle RPM, feed rate and material removal rate for CNC milling and routing. Pick a material for a sane starting point, then dial it to your machine.
Feeds and speeds depend heavily on your machine's rigidity and power, tool coating, depth of cut, and coolant. Start conservative, listen to the cut, and adjust. These presets assume carbide tooling.
The calculator above uses the standard milling formulas. You can also work them by hand.
RPM = SFM × 3.82 ÷ D, where SFM is surface feet per minute and D is the tool diameter in inches. (3.82 is 12 ÷ π, rounded.)IPM = RPM × chip load × flutes, where chip load is inches per tooth (IPT).SFM = RPM × D ÷ 3.82.RPM = Vc × 1000 ÷ (π × D), where Vc is the cutting speed in metres per minute and D is the tool diameter in mm.Vf (mm/min) = RPM × fz × z, where fz is the feed per tooth in mm and z is the number of flutes.Worked example: a 1/4 in, 2-flute carbide end mill at 600 SFM gives 600 × 3.82 ÷ 0.25 ≈ 9,170 RPM. At a chip load of 0.002 in, the feed is 9,170 × 0.002 × 2 ≈ 37 IPM. If your spindle cannot reach the calculated RPM, run at its maximum and scale the feed down with it so the chip load stays the same.
Typical conservative surface speeds for milling, as commonly published for general-purpose end mills. Use them as starting points, then adjust for your machine, tool coating, depth of cut and coolant. Tool makers' own data for a specific cutter takes priority.
| Material | Carbide SFM | Carbide m/min | HSS SFM | HSS m/min |
|---|---|---|---|---|
| Aluminium alloys (6061, 5052) | 600–1,000 | 185–305 | 250–500 | 75–150 |
| Brass | 400–800 | 120–245 | 150–300 | 45–90 |
| Copper | 300–600 | 90–185 | 100–200 | 30–60 |
| Mild / low-carbon steel | 250–450 | 75–135 | 70–100 | 20–30 |
| Alloy and tool steel (pre-hardened) | 150–300 | 45–90 | 40–70 | 10–20 |
| Stainless steel (304, 316) | 150–300 | 45–90 | 40–80 | 10–25 |
| Titanium alloys | 100–200 | 30–60 | 30–50 | 10–15 |
| Grey cast iron | 250–450 | 75–135 | 50–100 | 15–30 |
| Acrylic and rigid plastics | 500–1,000 | 150–305 | 300–500 | 90–150 |
| Hardwood, plywood and MDF (router) | 1,000–2,000 | 305–610 | 500–1,000 | 150–305 |
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