Importance

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Abstract

A shaft member for hydrodynamic bearing apparatuses having higher dimensional accuracy produced at low costs and a method for producing the same are provided. Moreover, a shaft member for hydrodynamic bearing apparatuses having hydrodynamic grooves processed with high accuracy and a method for producing the same are provided without a large increase in the processing costs. A shaft material 10 integrally having a shaft portion 11 and a flange portion 12 is formed by a forging process, and the cylindricity of a part or the entire outer circumferential surface 11a of the shaft portion 11 is corrected. The end face 11b of the shaft portion of the shaft material 10 and the end face 12b of the flange portion 12 on the opposite side of the shaft portion are ground relative to the corrected face 13 mentioned above, and the outer circumferential surface 10b of the shaft material 10 is ground relative to these end faces 11b, 12b. This renders the cylindricity of the radial bearing faces 23a, 23b formed on the outer periphery of the shaft portion 21 of the produced shaft member 2 to be 3 .mu.m or lower. Moreover, in a common forging step, a shaft material 110 integrally having the shaft portion 111 and flange portion 112 is formed, while simultaneously thrust hydrodynamic groove regions 112a, 112b are formed on both end faces of the flange portion 112. After the forging process, in a common rolling step, radial hydrodynamic groove regions 113a, 113b are formed on the outer circumferential surface 111a of the shaft portion 111. In a grinding step following the rolling process, the radial hydrodynamic groove regions 113a, 113b and the thrust hydrodynamic groove regions 112a, 112b are ground.

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First Claim