CNC Feed Rate

Calculating feed rate

For milling, multiply feed per tooth by the number of effective teeth and spindle revolutions per minute. A feed of 0.1 mm per tooth with four effective teeth at 1000 rpm gives 400 mm per minute. Effective teeth are the edges contributing to the same cutting path in each revolution. This is different from the number of teeth touching the workpiece at one instant.

Turning and drilling

These operations use feed per revolution. At 600 rpm and 0.25 mm per revolution, feed rate is 150 mm per minute. Do not multiply by two again because a drill has two edges. The result assumes constant feed. Tool centre feed adjustments for tight arcs or circular interpolation require a separate calculation.

Match feed per tooth with feed per revolution

For example milling, use spindle speed 1500 revolutions per minute, feed per tooth 0.08 mm and 3 effective teeth. Feed per revolution is 0.08 × 3 = 0.24 mm and feed speed is 0.24 × 1500 = 360 mm/min. The other mode at the same speed and 0.24 mm/rev should give the same feed speed. This checks the interpretation of units. The numbers are not cutting condition recommendations.

Feed per tooth cannot be entered directly as feed per revolution. Multiplying tooth count twice needlessly increases feed speed. Check the machine setting to establish whether the programmed command uses feed per minute or per revolution. The calculated unit must match the command's expected unit.

The output is linear feed speed, not the peripheral cutting speed of an edge. If spindle speed changes while programmed feed per minute stays fixed, actual tooth load changes. Reassess feed after changing spindle speed. Acceleration, corner slowing and toolpath geometry affect actual instantaneous feed. This constant value does not guarantee machining time or tool life.

Frequently asked questions

How do you calculate feed rate for milling?

With an example spindle speed of 1000 rpm, feed per tooth 0.1 mm and 4 effective teeth, multiplying these values gives a milling feed rate of 400 mm/min. Effective teeth contribute to the same cutting path, and this preliminary calculation excludes circular tool centre feed correction and selection of suitable cutting conditions.

Calculate with these values