The method involves grinding more than one rotor arm at once with a specially formed grinding wheel.The surface at an angle of less than ninety degrees. The surface of the grinding wheel is an inversion of part of the rotor profile, preferably across its whole width (103). The grinding wheel itself is cut using a diamond cutting tool which has the same profile as the rotor over the width to be ground at once. Before grinding more than one rotor, the accuracy of the grinding wheel is checked by measuring a test rotor with a more than two points dimensional testing device.
