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Guide

How to calculate spindle speed and feed rate

Spindle speed and feed rate decide how fast the tool cuts, how long it lasts and how good the surface is. Both follow from the cutting speed recommended for the material and the tool.

Start from cutting speed

Cutting speed (Vc) is how fast the cutting edge moves past the material, in metres per minute. Your tool supplier gives a recommended range for each material and tool coating. Use that, not a guess.

The spindle speed formula

Spindle speed n in revolutions per minute equals the cutting speed multiplied by 1000 and divided by pi times the diameter in millimetres. For milling and drilling the diameter is the tool diameter. For turning it is the workpiece diameter.

n = (Vc × 1000) / (π × D)

The feed rate formula

For milling, the table feed rate in millimetres per minute equals the feed per tooth multiplied by the number of teeth and by the spindle speed. Feed per tooth also comes from the tool supplier.

Vf = fz × z × n

Worked example

A 20 mm cutter with 4 teeth runs at 150 m/min with 0.1 mm per tooth. The spindle speed is about 2387 rpm and the feed rate is about 955 mm/min.

Check the limits

Limit the result to the maximum spindle speed of the machine and the rated speed of the tool and holder. Reduce the speed and feed if the machine is not rigid enough or the workpiece vibrates.

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