Milling Feed, Chip Load & Material Removal Rate Calculator

How it works

n = Vc × 1,000 ÷ (π D) (ball nose: D_eff = 2√(ap(D − ap)) when ap < D/2); chip thinning: end mill 1 ÷ √(1 − (1 − 2ae/D)²) for ae < D/2, ball nose D ÷ D_eff, face mill 1 ÷ sin κr; vf = n × z × fz; hm = fz × (2ae/D) ÷ φ (φ = arccos(1 − 2ae/D), radians); MRR = ae × ap × vf ÷ 1,000 cm³/min; P (kW) = MRR × kc ÷ 60 ÷ efficiency; torque = P × 9,549 ÷ n

Milling parameters chain together from two numbers the tool maker gives you: the surface speed the carbide can stand in that material, which with the cutter diameter fixes the rpm, and the chip load each tooth should take, which with the flute count and rpm fixes the table feed. Depth and width of cut then set the material removal rate — the productivity number — and multiplying it by the material’s specific cutting energy gives the power, torque and cutting force, which you can check against the spindle. Geometry often thins the chip below the programmed feed per tooth: at light radial engagement with an end mill, with a ball nose cutting below its full diameter, and with a face mill whose inserts sit at a lead angle. The calculator raises the feed to keep the true chip at your target (you can switch that off) and reports the maximum and average chip thickness. A ball nose cutting shallow also runs on a smaller effective diameter, so the rpm is based on that. The stepover table shows how feed, removal rate and power change as the radial engagement grows, which is the trade-off behind high-efficiency and trochoidal milling. If the machine cannot reach the ideal rpm, the surface speed simply falls and the feed is recomputed at the available speed.

Worked example

A 12 mm four-flute carbide end mill in 6061 aluminium at 300 m/min wants 7,958 rpm. At 0.05 mm chip load with a 6 mm (50%) stepover there is no thinning, so the feed is 7,958 × 4 × 0.05 = 1,592 mm/min. An 8 mm depth gives 6 × 8 × 1,592 ÷ 1,000 = 76.4 cm³/min — about 0.89 kW at the cutter, 1.11 kW at the motor — and 1.07 N·m of torque. Drop the stepover to 1.2 mm (10%) and the chip thins, so the feed rises ×1.67 to 2,653 mm/min. In inch terms, Machining Doctor’s example of a ½ in 4-flute at 300 SFM, 0.004 in per tooth, 0.25 × 0.5 in cut gives 2,292 rpm, 36.7 in/min and 4.6 in³/min.

Sources: Sandvik Coromant — Milling formulas and definitions · Machining Doctor — Metal removal rate calculator · Harvey Performance — Chip thinning

Frequently asked questions