Method for machining ribs on air or gas bearings of a compressor

A method for machining ribs or grooves on a workpiece intended to be rotated about a longitudinal axis of a centrifugal compressor, the workpiece being at least one of a front air or gas radial bearing mounted on a first end of the shaft and a rear air or gas radial bearing mounted on a second end of the shaft, the centrifugal compressor further comprising a shaft made of tungsten carbide or ceramic, on which a rotor structure with at least one permanent magnet of an electric motor is attached in order to drive the shaft such that the shaft rotates, a casing with a fluid inlet and a compressed fluid outlet, a first impeller and a second impeller mounted at two ends of the shaft in the casing, the machining method being carried out in a machining unit adapted to receive the workpiece and comprising a tool holder with a tool for machining the ribs or grooves on at least one portion of the workpiece,

• wherein all of the ribs or grooves formed on a workpiece portion of the air or gas axial bearing are obtained at once by driving the workpiece such that it rotates by moving the workpiece or the tool holder in a machining direction for extending the grooves via the machining unit, and by moving said machining tool moving back and forth between a machining position in contact with the workpiece and a position wherein it is not in contact with the workpiece from the start to the end of the machining, and wherein, in accordance with a sinusoidal program, the machining unit rotates the workpiece to repeat forward and reverse rotations by continuously and sinusoidally changing the rotation angle of the workpiece while at least synchronising the rotation of the workpiece with the back-and-forth movements of the machining tool so that a determined arrangement of the ribs or grooves are produced on the air or gas axial bearing.