Find spindle speed from cutting speed and diameter, then the feed rate for milling, drilling and turning.

The right Vc and fz depend on the work material, the tool's material and coating, and how rigid the setup is. Always start from the tool maker's catalogue values.

How it is calculated

The cutting speed is how fast the surface of the tool (milling and drilling) or of the work (turning) moves past the cutting edge. The spindle speed that gives the wanted cutting speed is

n = \frac{1000\,V_c}{\pi D}

The 1000 converts metres to millimetres. The feed rate per minute is

v_f = f_z \cdot z \cdot n \quad \text{(milling / drilling)} \qquad v_f = f \cdot n \quad \text{(turning)}

where

$n$ is the spindle speed (rpm)
$V_c$ is the cutting speed (m/min)
$D$ is the tool diameter (milling / drilling) or the work diameter at the cut (turning) (mm)
$v_f$ is the feed rate (mm/min)
$f_z$ is the feed per tooth (mm/tooth)
$z$ is the number of teeth on the tool
$f$ is the feed per revolution (mm/rev)

If the calculated speed is over the machine's maximum, the result uses the maximum instead and shows the actual cutting speed, which is lower than the one set. Turning at constant surface speed (G96) must always limit the maximum speed with G50.

Spindle speed and feed rate

How it is calculated