Cutting Power & Spindle Torque Calculator
Power from removal rate and specific cutting force, torque from power and RPM — then the check no generic calculator offers: which of our actual spindles can deliver it, from the 22 kW Puma turning centres down. Reverse mode: your machine’s power → the removal rate it can sustain.
Editable — your tooling supplier’s value beats this band.
From the feeds & speeds calculator.
Motor kW ratings are before drivetrain losses; ~80% is typical.
Cutting power: the arithmetic and the honest caveats
The estimate is one line: P (kW) = MRR × kc ÷ 60000, removal rate in cm³/min and specific cutting force in N/mm². Torque follows as T = 9550 × P ÷ RPM. A 19 cm³/min cut in steel at kc 2100 wants about 0.67 kW at the edge — trivial — but the same removal rate roughing a superalloy at kc 3200 and low RPM is a very different torque story, which is why power limits bite at low speed even when the kW figure looks comfortable.
kc is the soft number. It is not a material constant: it falls as chip thickness rises (thin chips waste energy ploughing), and it moves with rake angle, edge prep and wear. Aluminium sits somewhere near 700–900 N/mm², steels around 1800–2400, stainless higher, nickel alloys higher still — but a sharp positive-rake cutter at a healthy chip load can beat the band, and a worn insert at a timid feed can blow through it. Treat the band as a sanity envelope, and the number your insert supplier publishes as the answer.
The practical use of this tool is capacity planning against a real machine list. Our heaviest spindles are the 22 kW Puma turning centres; the DVF 5000 five-axis carries 17 kW. At 80% drivetrain efficiency and steel kc, that caps sustainable removal around 400 cm³/min on the lathes — and any cut whose calculated demand approaches the badge rating should be treated as a duty-cycle question, because continuous ratings sit below the 15-minute headline figure. If the reverse tab says your cut does not fit, the fix is depth or feed, not optimism.
Cutting power — FAQ
How do you calculate cutting power?
P (kW) = material removal rate (cm³/min) × specific cutting force kc (N/mm²) ÷ 60000, then divide by spindle efficiency (~0.8) for the motor power needed. 30 cm³/min in steel at kc 2100 needs about 1.05 kW at the edge, ~1.3 kW at the motor.
How do you calculate spindle torque from power?
T (Nm) = 9550 × P (kW) ÷ RPM. Ten kW at 500 RPM is 191 Nm; the same 10 kW at 10,000 RPM is under 10 Nm — which is why low-speed, large-diameter work is torque-limited rather than power-limited.
What is specific cutting force (kc)?
The energy needed to remove one cubic millimetre of material, in N/mm². It depends on the material AND the chip thickness, rake and edge condition (the Kienzle relationship) — typical bands: aluminium 700–900, steels 1800–2400, stainless 2200–2800, nickel superalloys 2800–3500.
How much material can a 15 kW spindle remove?
Max MRR ≈ kW × efficiency × 60000 ÷ kc. At 80% efficiency in steel (kc 2100): 15 × 0.8 × 60000 ÷ 2100 ≈ 343 cm³/min — less in practice once duty cycle and stability enter.
Why does my machine stall below its rated power?
Spindle ratings are duty-cycle rated (S6/15-min figures on the badge exceed continuous S1), and at low RPM the limit is torque, not power. Check the machine’s torque curve, not just the kW number.
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