Clamp for disk rotation driving device and method of manufacturing clamp

A clamp for a disk rotation driving device comprising, 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, the clamp further comprising:

• a centering cylinder bent from the central part of the clamp in an axial direction and having a thickness equal to a thickness of the central part and a circumferential inner surface defining the centering hole in the axial direction;
• and
• a rounded section provided along an edge of the centering hole so as to be rounded from a bended end of the centering cylinder that extends with the centering cylinder bend from the central part of the clamp, the rounded section having a radius smaller than the thickness of the centering cylinder,
• the fastening surface being continuous to and adjoining the rounded section so that the fastening surface comprises an extension having a thickness within a range of the thickness of the centering cylinder relative to the radius of the rounded section,
• the circumferential inner surface being continuous to and adjoining the rounded section so that the circumferential inner surface comprises an extension having a thickness within a range of the thickness of the central part relative to the radius of the rounded section, and
• the extensions of the fastening surface and circumferential inner surface comprise the same width in an extended direction thereof.