As shown in the formula below, feed is ℓ (cutting length per minute) ÷n (main axis spindle speed). (Cutting length per minute) ÷ (RPM) is the movement of the cutting edge during one work rotation.

Feedrate formula

When machining a 10 mm diameter shaft, lets says a 100 mm length is machined in 1 minute, at 1,000 RPM. This means that the cutting length per minute is 100 mm/min.

Cutting speed (when turning) is the peripheral speed of the work and the amount of insert movement in metres per minute. (π x Dm) of the formula below is the periphery of the work. The periphery x n (RPM) is millimeters the cutting edge moves on the periphery of the work in a minute. It is usually expressed in m/min. Divide by 1,000 to change to m from mm.