Abstract: Hard metal cutting blades are inserted into grooves of the rotor body. Each cutting blade is provided at both ends thereof with a cylindrical or conical clamping surface, to which a conical surface of a conical screw is applied which clamps the blade within the groove by a clamping force. The cutting blades are thus securely held in a definite position not only radially and circumferentially, but also axially. The shape of the cutting blades and the grooves as well as the clamping means, having the shape of conical screws, are simple and unexpensive, and their handling is simple. A soiling of the cutting blade clampings is virtually excluded.