Patent ID: 8339745

Claim:
A method for manufacturing a baseplate comprising a boss portion configured to be inserted into a mounting hole of an actuator arm of a disk drive, the method comprising: press-forming the baseplate formed from austenite stainless steel, thereby forming the boss portion in a shape of a cylinder comprising a ball insertion hole, and work-hardening the boss portion; heat-treating the work-hardened baseplate, thereby reducing a hardness of the boss portion; and immersing the baseplate in a chemical polishing liquid after the heat-treating to perform chemical polishing, thereby forming a chemically-polished surface on an inner circumferential wall of the ball insertion hole; wherein: the chemically-polished surface has an oxygen-rich layer, an oxygen concentration of the oxygen-rich layer being higher than a chromium concentration near a surface thereof; and a thickness of the oxygen-rich layer is reduced with respect to a thickness of the oxygen-rich layer before the chemical polishing, thereby making a frictional resistance when a ball is inserted in a direction in which the boss portion is pulled smaller than a frictional resistance when the ball is inserted in a direction in which the boss portion is compressed.