Milling speed and feed calculator
Pick the material and cutter and this returns spindle speed and feed rate. Treat the result as a starting point: rigidity, holder runout, coolant and how much the cutter is engaged all move the real numbers.
If the cut chatters, reduce depth of cut before reducing feed. Backing the feed off while keeping the speed up rubs rather than cuts, which work-hardens the material and destroys the edge.
- Spindle speed
- 3,056 rpm
- Feed rate
- 33.6 in/min
At 400 SFM. Cap this at whatever your spindle will actually hold.
Chipload 0.0027 in per tooth. A starting point, not a final number: adjust to the chip and the sound of the cut.
Cutting speeds by material
Surface speed, in feet per minute at the cutting edge, is a property of the material and the tool, not the machine. Carbide runs three to five times faster than high speed steel in the same material.
These are conservative starting figures for slotting and general milling with coolant. Light finishing passes can run higher.
| Material | HSS (SFM) | Carbide (SFM) |
|---|---|---|
| Aluminium 6061 | 250 to 350 | 600 to 1,200 |
| Brass | 200 to 300 | 500 to 900 |
| Mild steel 1018 | 80 to 110 | 300 to 500 |
| Alloy steel 4140 | 50 to 70 | 200 to 350 |
| Stainless 304 | 40 to 60 | 150 to 300 |
| Cast iron | 60 to 80 | 200 to 350 |
| Titanium | 25 to 40 | 100 to 200 |
| Hardened steel 45 HRC | Not suitable | 80 to 150 |
End mill chipload
Chipload is how thick a chip each tooth takes. Too small and the cutter rubs, generating heat and work-hardening the surface. Too large and the edge chips or the tool deflects.
Reduce chipload by about half when slotting at full width, and when cutting deeper than one diameter.
| Cutter dia | Aluminium | Mild steel | Stainless |
|---|---|---|---|
| 1/8 in | 0.0010 | 0.0005 | 0.0004 |
| 3/16 in | 0.0018 | 0.0009 | 0.0007 |
| 1/4 in | 0.0025 | 0.0012 | 0.0010 |
| 3/8 in | 0.0040 | 0.0020 | 0.0016 |
| 1/2 in | 0.0055 | 0.0030 | 0.0024 |
| 3/4 in | 0.0080 | 0.0045 | 0.0035 |
| 1 in | 0.0100 | 0.0060 | 0.0045 |
The formulas
Spindle speed in imperial: RPM = (SFM x 12) / (pi x D), which simplifies to RPM = SFM x 3.82 / D with D in inches.
Spindle speed in metric: RPM = (Vc x 1000) / (pi x D), with Vc in metres per minute and D in millimetres.
Feed rate: IPM = RPM x chipload x number of flutes. In metric, mm/min = RPM x chipload in mm x flutes.
To convert, 1 SFM is 0.3048 metres per minute.
