A method of determining a machining axis of a rotary work blank which includes workpiece areas to be machined by stock removal and areas to be left unmachined and whose nominal mass distribution is known, by means of a measurement device capable of measuring the spatial position of workpiece surface points, said method comprising the steps of: Receiving a reference workpiece (50, 60) in the seats of the measurement device; Measuring, by means of the measurement device, the position of a plurality of points of surface areas of the reference workpiece (50, 60) to be left unmachined relative to an imbalance reference axis determined in the measurement device; Storing, in a data memory of a computer, the measured position data of the plurality of points of surface areas of the reference workpiece (50, 60) to be left unmachined as reference partial surface; Removing the reference workpiece (50, 60) from the measurement device; Receiving a work blank in the seats of the measurement device; Measuring, by means of the measurement device, the position of a plurality of points of surface areas of the work blank to be left unmachined; Storing, in the data memory of the computer, the measured position data of the plurality of points of surface areas of the work blank to be left unmachined as blank partial surface; Computing, from the stored position data, an imbalance effect relative to the imbalance reference axis which results from the deviation between blank partial surface and reference partial surface; Expressing the imbalance effect by the position of the main inertia axis of an assumed workpiece having nominal mass distribution; and Computing of the machining axis by adding an offset to the position of the main inertia axis, which offset is determined empirically with reference to imbalances, measured relative to the machined workpiece axis, of a plurality of workpieces manufactured with a machining axis determined according to the method, and is stored it in the computer. Receiving a reference workpiece (50, 60) in the seats of the measurement device; Measuring, by means of the measurement device, the position of a plurality of points of surface areas of the reference workpiece (50, 60) to be left unmachined relative to an imbalance reference axis determined in the measurement device; Storing, in a data memory of a computer, the measured position data of the plurality of points of surface areas of the reference workpiece (50, 60) to be left unmachined as reference partial surface; Removing the reference workpiece (50, 60) from the measurement device; Receiving a work blank in the seats of the measurement device; Measuring, by means of the measurement device, the position of a plurality of points of surface areas of the work blank to be left unmachined; Storing, in the data memory of the computer, the measured position data of the plurality of points of surface areas of the work blank to be left unmachined as blank partial surface; Computing, from the stored position data, an imbalance effect relative to the imbalance reference axis which results from the deviation between blank partial surface and reference partial surface; Expressing the imbalance effect by the position of the main inertia axis of an assumed workpiece having nominal mass distribution; and Computing of the machining axis by adding an offset to the position of the main inertia axis, which offset is determined empirically with reference to imbalances, measured relative to the machined workpiece axis, of a plurality of workpieces manufactured with a machining axis determined according to the method, and is stored it in the computer.