Base member, spindle motor including base member, hard disk drive device, and method for manufacturing base member
A base member includes a projection having a cylindrical shape and projecting in an axial direction and a component placement part. The projection and the component placement part are adjacent to each other via a curved surface part having a first curved surface and a second curved surface. The first curved surface and the second curved surface have a diameter increasing toward the component placement part in the axial direction. The second curved surface is located closer to a side of the component placement part than the first curved surface in the axial direction.
1 . A base member, comprising:
a plurality of combinations of a projection and a component placement part, the projection having a cylindrical shape and projecting in an axial direction,
wherein
the projection and the component placement part are adjacent to each other via a curved surface part having a first curved surface and a second curved surface,
the first curved surface and the second curved surface have a diameter increasing toward the component placement part in the axial direction,
the second curved surface is located closer to a side of the component placement part than the first curved surface in the axial direction
the first curved surface is continuous with the second curved surface in the axial direction and in a radial direction,
the combinations of the projection and the component placement part having the substantially same dimension in the axial direction, and
a difference between a maximum value in the plurality of combinations and a minimum value in the plurality of combinations of a height in the axial direction of a boundary surface between the component placement part and the second curved surface is smaller than a difference between a maximum value in the plurality of combinations and a minimum value in the plurality of combinations of a height in the axial direction of a boundary surface between an outer peripheral surface of the projection and the first curved surface.
2 . The base member according to claim 1 , wherein the component placement part comprises a cutting trace including continuous arcs not centered on a central axis of the projection.
3 . The base member according to claim 2 , wherein the second curved surface comprises the cutting trace including the continuous arcs not centered on the central axis of the projection.
4 . The base member according to claim 1 , wherein the first curved surface and the second curved surface have a position in the axial direction approaching an upper end part of the projection as the first curved surface and the second curved surface approach the projection in the radial direction.
5 . The base member according to claim 1 , wherein a boundary between the first curved surface and the second curved surface does not project outward from a substantially truncated cone shape surrounded by a boundary between the projection and the first curved surface and a boundary between the second curved surface and the component placement part.
6 . The base member according to claim 1 , wherein the first curved surface and the second curved surface have a substantially arc-like cross-sectional shape and are formed in an annular shape surrounding the projection.
7 . The base member according to claim 1 , wherein,
a difference between a value largest in the plurality of combinations and a minimum value in the plurality of combinations of a distance from the central axis of the projection in the radial direction of a boundary surface between the first curved surface and the second curved surface is larger than a difference between a maximum value in the plurality of combinations and a minimum value in the plurality of combinations of a distance from the central axis of the projection in the radial direction of a boundary surface between the outer peripheral surface of the projection and the first curved surface.
8 . The base member according to claim 1 , wherein a height of a casing is from 1.5 to 2.0 inches.
9 . A spindle motor comprising the base member according to claim 1 .
10 . A hard disk drive device comprising the spindle motor according to claim 9 .
11 . The hard disk drive device according to claim 10 , wherein a gas having a lower density than air is sealed in an internal space.