Abstract: It is an object of the present invention to provide a motor capable of reducing a loss as much as possible, and securing minimum vibration proof performance and reliability by definitely defining the upper and lower limits of a minimum shaft diameter in conformity with a disk load, the service number of revolutions or the like. In a shaft-fixed type motor of the fluid bearing specifications, the diameter d (mm) of a fixed shaft is set so as to satisfy the relation of &agr;3·M1 >d3>M1, where M1=J1·(N/1000)2·k2·D, J1 being a coefficient to be experimentally determined, N(rpm) the service number of revolutions, k the number of a disk-shaped recording media, D (inch) the diameter of the disk-shaped recording medium, and &agr; a ratio of the maximum diameter to the minimum diameter of the fixed shaft.

Abstract: In a spindle motor for a driving a memory disk, a is closed space formed by a sleeve metal, an end portion of a shaft and a thrust plate. The closed space is connected to outside open space by a connection path, thereby effectively discharging undesirable air in an assembling stage.

Abstract: A spindle motor has a tapped hole formed in the end surface of a rotor hub at the center of rotation of the rotor hub. A clamping member presses a disk against a disk holding surface of the rotor hub by a clamp screw threaded in the tapped hole. Since the disk is clamped through a clamping member by threading and tightening one clamp screw, the clamping operation is efficiently carried out and disk imbalance due to the clamping clamp screw is decreased.

Abstract: In a spindle motor for a driving a memory disk, a closed space is formed by a sleeve, an end portion of a shaft and a thrust plate. The closed space is connected to outside open space by a connection path, thereby effectively discharging undesirable air in an assembling stage.

Abstract: A cylindrical shielding plate is provided on an inner circumference of the cylindrical recess formed on the bracket of an electric motor of a magnetic disk drive, and an open sector of the stator core is arranged to coincide with the moving direction of read/write head. Or a cylindrical boss is inserted between the stationary shaft and the stator core. Thereby, high frequency electromagnetic noise to the magnetic disk is drastically reduced.