586,100. Centrifugal compressors. MEISSER, C. Dec. 8, 1944, No. 24597. Convention date Dec. 30, 1943. [Class 110 (i)] [Also in Group XXII] In a helico-centrifugal compressor in which the general surface of the rotor is conical or. one described by a curved line convex to the rotor axis, each side of a blade has a uniform screw pitch but the pitches of the two sides differ so as to give the same blade thickness at the inlet and outlet. At the outlet end the blades are cut away to a streamline form ; this being effected on the trailing or suction side at the tip and the base and on the leading or pressure side at the middle region. The centre line of the cross-section of the blades is everywhere radial to the axis and the cross-section is such as to give approximately uniform strength. The blades may be cut in a milling machine as shown in Fig. 2. The shaft 20 which carries the rotor 30 is traversed together with a frame 24 carrying a template 25 by means of a leading screw on a shaft 14 and the shaft 20 is simultaneously rotated by gearwheels 18, 22. In one method, a milling cutter of double angle equal to about 15‹ is used. It is displaced forwardly in the direction of rotation of the rotor 30 for cutting the leading side of a blade and backwardly for cutting the trailing side. By this means the blades are given a uniform peripheral width over their length. In another method, a milling cutter of double angle equal to 30‹ or more is used and is not displaced.