Patent ID: 8522588

Claim:
A method of manufacturing a clamp for a disk rotation driving device including a central part and peripheral part, a centering hole formed through the central part, a contact portion circumferentially formed along the peripheral part, a fastening surface formed at the central part, the centering hole being fitted to an outer circumference of a centering projection circumferentially formed on a rotor to be rotary driven, and the clamp being fixed to the rotor with a clamping screw that is clamping screwed into an axial center of the rotor so that a fastening head of the clamping screw fastens the fastening surface of the clamp toward the rotor and so that the contact portion comes in contact with an information recordable disk attached to the rotor and applies pressing load onto the disk in a rotation axis direction, a centering cylinder bent in an axial direction and having a circumferential inner surface defining the centering hole in the axial direction, and a rounded section provided along an edge of the centering hole at a portion of the centering cylinder bent in the axial direction and having a radius smaller than a wall thickness of the centering cylinder, the fastening surface being continuous to and adjoined with the rounded section, and the method comprising: forming a semi-finished cylindrical portion bent from the central part in the axial direction so that the semi-finished cylindrical portion comprises a length that is larger than a length of the centering cylinder in the axial direction; pressing the semi-finished cylindrical portion into the centering cylinder so that material movement of the clamp material is caused throughout the semi-finished cylindrical portion and so that a wall thickness of the semi-finished cylindrical portion is obtained that is the same as a thickness of the central part in the axial direction without extension of the semi-finished cylindrical portion away from the central part in the axial direction; shaping the radius of the rounded section at the bent portion of the centering cylinder as a result of the material movement of the clamp material when pressing the semi-finished cylindrical portion into the centering cylinder.