Cutting Power and Spindle Torque
Cutting horsepower, motor horsepower after drive efficiency.
Example
You enter
- Material removal rate (in3/min) 3
- Unit power (hp per in3/min) 1
- Spindle drive efficiency (%) 80
- Spindle speed (rpm) 800
You get
- Cutting horsepower 3 hp
- Motor horsepower needed 3.75 hp
- Spindle torque 19.7 lb-ft
Checked against published worked examples from: East Tennessee State University (G. Stanton and B. Hemphill), ENTC 3710.
Details, formula, and sources
ScopeCutting horsepower, motor horsepower after drive efficiency, and spindle torque from the material removal rate and the specific cutting energy (unit power: about 1.0 carbon steel, 0.33 aluminum, 1.5 stainless/titanium) -- the stall / motor-size check before a heavy cut. The tool and machine govern the real draw.
Formula or tableCutting horsepower = MRR (in3/min) x unit power (hp per in3/min); motor horsepower = cutting hp / (efficiency / 100); spindle torque (lb-ft) = 5252 x cutting hp / rpm.
Source and editionCutting power and spindle torque - first-principles specific-cutting-energy relation with Machinery's Handbook (Industrial Press) unit-power values, by name; the 5252 torque constant is universal.
Free accessThe specific-cutting-energy arithmetic is public; the material removal rate, unit power, efficiency, and rpm are user-supplied.
What governsEstimate. AHJ and licensed professional govern.
API field namesmrr_in3_min, unit_power_hp, efficiency_pct, rpm, cutting_hp, motor_hp, spindle_torque_lbft
- Unit power specific cutting energy, hp per in3/min: ~1.0 carbon steel, ~0.33 aluminum, ~1.5 stainless/titanium; default 1.0Machinery's Handbook
- Drive efficiency spindle drive efficiency; default 80%machine data