Spindle speed, table feed rate, material removal rate, cutting power and cycle time for CNC milling. Enter your own cutting speed or let the calculator pick a starting value from the workpiece and tool material.
Cutting speed is a property of the material pair, not of the machine. Everything else follows from it: spindle speed comes from the tool diameter, feed rate from the chip load and flute count, and power from how fast material is actually being removed.
Vc cutting speed (m/min) ·
D tool diameter (mm) ·
z number of flutes ·
fz chip load (mm/tooth) ·
ap axial depth (mm) ·
ae radial depth (mm) ·
kc specific cutting force (N/mm²)
A 10 mm four-flute carbide end mill slotting mild steel at 5 mm radial and 2 mm axial depth, 0.05 mm/tooth chip load.
At 0.32 kW this is a light cut for any industrial spindle. Running the same geometry in titanium is instructive: cutting speed drops from 200 to 50 m/min, so spindle speed falls to 1 592 rpm and feed to 318 mm/min. Material removal rate drops to 3.18 cm³/min — a quarter — while specific cutting force doubles to 3 000 N/mm². Net cutting power comes out at 0.159 kW, half that of mild steel. Titanium is not power-hungry per minute; it is slow. The cost is cycle time, not spindle load.
| Quantity | Symbol | Unit | Accepted range |
|---|---|---|---|
| Cutting speed | Vc | m/min or SFM | > 0 |
| Tool diameter | D | mm | > 0 |
| Number of flutes | z | — | ≥ 1 |
| Chip load | fz | mm/tooth | > 0 |
| Axial depth | ap | mm | > 0 |
| Radial depth | ae | mm | > 0 and ≤ D |
| Spindle speed | n | rpm | output, flagged above 30 000 |
| Feed rate | f | mm/min | output |
| Cutting power | Pc | kW | output |
Surface feet per minute is converted at 1 SFM = 0.3048 m/min. Radial depth above 75 % of tool diameter raises a high-engagement warning, and radial depth greater than the tool diameter is rejected.
| Workpiece | Vc carbide (m/min) | Vc HSS (m/min) | kc (N/mm²) |
|---|---|---|---|
| Aluminium | 600 | 150 | 700 |
| Copper | 300 | 75 | 900 |
| Mild steel | 200 | 50 | 1 500 |
| Cast iron | 180 | 45 | 1 100 |
| Alloy steel | 150 | 38 | 2 200 |
| Stainless steel | 120 | 30 | 2 500 |
| Titanium | 50 | 13 | 3 000 |
Spindle speed in rpm equals 1000 × cutting speed in m/min ÷ (π × tool diameter in mm). A 10 mm cutter running at 200 m/min needs 6 366 rpm. Cutting speed is a property of the workpiece and tool material combination, so the same cutter runs at very different speeds in aluminium and titanium.
Chip load is the thickness of material each cutting edge removes per revolution, written as fz in mm per tooth. Table feed rate is chip load × number of flutes × spindle speed. Running too light rubs rather than cuts and work-hardens the surface, especially in stainless steel, while running too heavy overloads the edge and chips it.
Material removal rate is the volume of material cut per minute, calculated as radial depth × axial depth × feed rate. It is the honest measure of productivity, because a high spindle speed with a light cut can remove less material than a slower, heavier one. It also drives spindle power demand, so it is the number to watch when deciding whether a cut is within a machine's capability.
Cutting power is the specific cutting force of the material multiplied by the material removal rate. Specific cutting force ranges from about 700 N/mm² for aluminium to 3 000 for titanium, which is why titanium demands far more power for the same volume removed. Compare the calculated figure against the spindle rating, allowing for drive efficiency, and leave headroom rather than running at the limit.
Cutting speed depends on the workpiece material and the tool material. For carbide tooling typical starting points are 600 m/min in aluminium, 200 in mild steel, 180 in cast iron, 150 in alloy steel, 120 in stainless and only 50 in titanium. High speed steel tooling runs at roughly a quarter of these figures. Always check the tooling manufacturer's data for the specific grade and coating.