Drill Speed, Feed, Power, and Torque

Drilling is fed in inches per REVOLUTION rather than per tooth, because a drill's two lips both cut on the same revolution and the feed per revolution is what sets the chip thickness on each -- which is the difference between this and a milling speeds-and-feeds calculation. The removal rate is the full hole cross-section times the feed rate, since a drill cuts the entire circle, and that is why a drill of a given diameter removes far more material per minute than an end mill of the same diameter. The torque line is the one that matters on a hand-fed machine or a mag drill. Power is modest and torque is not: a half-inch drill in mild steel at 80 surface feet per minute and 0.006 in per revolution turns 611 rpm, feeds 3.67 in/min, removes 0.72 cubic inches a minute, takes 0.72 hp at the cut and 0.90 at the motor, and produces 74 in-lb of spindle torque. Torque rises with the SQUARE of diameter at constant surface speed and feed per revolution, so a one-inch drill at the same settings takes four times the torque -- which is why a drill press that handles a half-inch bit throws the work out of the vise with a one-inch one, and why the workholding rather than the motor is usually the real limit. A shop estimate; the tool manufacturer's published speeds and feeds, the machine's rating, and the workholding govern.

rpm = 3.82 x sfm / diameter_in; feed_ipm = feed_ipr x rpm; removal_rate_cipm = pi (D/2)^2 x feed_ipm; power_at_cut_hp = removal_rate x unit_power; motor_power_hp = power_at_cut / spindle_efficiency; torque_in_lb = 63,025 x power_at_cut / rpm.

Drilling speed and feed from the standard shop relations, with power from the material's unit power and torque from 63,025 x hp / RPM, by name (the Machinery's Handbook method). Feed is per REVOLUTION, not per tooth. The tool manufacturer's published speeds and feeds, the machine's rating, and the workholding govern.

The speed, feed, and power relations are public shop arithmetic; the unit power for the material and the spindle efficiency are entered rather than bundled from any table.

Estimate. AHJ and licensed professional govern.

Field names used by the API: diameter_in, sfm, feed_ipr, unit_power, spindle_efficiency, rpm, feed_ipm, removal_rate_cipm, power_at_cut_hp, motor_power_hp, torque_in_lb

• Feed per revolution drilling is fed in IPR, not per tooth; both lips cut on the same revolutionshop machining practice
• Full-circle removal the removal rate is the whole hole area times the feed rateshop machining practice
• Torque goes as D squared at constant SFM and IPR, doubling the diameter quadruples the spindle torquethe speed and power relations combined