A spindle motor of the present invention is capable of keeping its ball
(5a, 5b)'s pre-load constant, because a sleeve (6) is capable of being
resiliently deformed due to its resiliency, and therefore capable of
constantly keeping a pre-load applied to the balls (5a, 5b) from inner and
inner ring raceways of inner and outer rings (3a, 4a, 3b, 4b) of ball
bearings (3, 4). In this motor, a rotor hub (7) has an axial center bore
(8). This bore (8) is provided with: a large-diameter bore portions in its
opposite axial ends; and, a small-diameter bore portion (8a) axially
interposed between the large-diameter bore portions. An inner diameter of
the small-diameter bore portion (8a) is smaller than an outer diameter of
the sleeve (6). The axial center bore (8) of the hub (7) is fitted to an
outer peripheral surface of the sleeve (6) in an insertion manner through
a heating shrinkage fit process, so that the sleeve (6) is subjected to a
radially inwardly exerted pressure applied from outside to resiliently
deform radially inwardly. As a result, a small-diameter portion (6a) is
formed in the sleeve (6) to extend radially inwardly between the outer
rings (3b, 4b).
