Disk drive spindle hub assembly

A disk drive for magnetic data storage media includes a spindle bearing arrangement having a rotatable portion surrounding and mounted by bearings on a stationary portion. A spindle hub having a cylindrical outer surface and a concentric interior cavity is rigidly attached to the rotatable portion of the spindle bearing arrangement. The cylindrical outer surface of the spindle hub provides a mounting surface for a stack of storage disks. A brushless direct current motor is mounted within the hub cavity. The rotor of the motor includes a sleeve rigidly attached to the floor of the spindle hub cavity and providing a return flux path for the motor. The spindle hub and the sleeve have distinct coefficients of thermal expansion and a radial spacing between the sleeve and the spindle hub allows for unconstrained thermal expansion of the sleeve and the spindle hub. The hub cavity floor incorporates a concentric annulus for accurate centering of the sleeve within the cavity.