Abstract: A method and apparatus for manufacturing laminated rotor cores in which lamina thickness variations are compensated for without disturbing the relative alignment of lamina shaft holes throughout the rotor core. The rotor core includes several truing laminas which are rotated to compensate for the lamina thickness variations and which include a central opening larger than the lamina shaft holes. The enlarged central opening in the truing laminas prevents overlap between the central opening and the shaft holes after rotation in spite of a lack of concentricity of the lamina shaft holes and central openings with respect to the laminas.

Abstract: A method of progressive die stamping for cutting apertures in a sheet metal strip without producing stress induced distortion of the apertures after cut-off of the strip. The sheet metal strip is peened to form one dent between the aperture and one edge of the strip and to form another dent between the aperture and the other edge of the strip and subsequently cutting the strip with a cut-off punch. The peening operation may be done before, during or after the aperture punching operation.