Abstract: A bearing shell comprising a body with a clearance hole defined by an inner wall of the body. The bearing shell further includes at least a first bearing surface and at least a second bearing surface. The first bearing surface is located on a first end and the second bearing surface is located on a second end of the body. In order to provide a bearing shell of simpler design, the first bearing surface and the second bearing surface, particularly shaped out of the body, are offset to each other in radial direction.

Abstract: A disk drive including a disk drive base having a lower portion and a base post extending upwardly from the lower portion, a rotatable spindle attached to the disk drive base, and a head actuator pivotally attached to the disk drive base. The head actuator includes an actuator body having a bore therein, and an actuator pivot bearing disposed at least partially within the bore, the actuator pivot bearing having a cover attachment member extending at least partially into a distal end of the base post. An upper portion of the pivot shaft includes an annular groove and a lower portion of the pivot shaft includes an annular recess.

Abstract: An actuator pivot assembly for a multi-actuator shared shaft data storage device may include a shared pivot shaft around which a first rotary actuator assembly is coupled, with a first bearing assembly interposed therebetween with a first bearing preload, and around which a second rotary actuator assembly is coupled, with a second bearing assembly interposed therebetween with a second different bearing preload. Furthermore, the first bearing assembly may have a first bearing span and the second bearing assembly may have a second bearing span that is different from the first bearing span. Each of the foregoing bearing features may thereby assist with spacing apart the structural resonance frequencies of the actuator assemblies to inhibit transmission of vibration between the actuators during operation.

Abstract: A pivot assembly bearing includes: a sleeve, a shaft inserted into the sleeve, a pair of rolling bearings disposed between the sleeve and the shaft such that the rolling bearings are separated apart from each other in an axial direction. The rolling bearings include an inner ring fixed to the shaft, an outer ring fixed to the sleeve, and a rolling element provided between the inner ring and the outer ring. In at least one of the rolling bearings, a first sealing member contacts an end face of the outer ring facing an outer side in the axial direction. Thus, a first labyrinth gap between the first sealing member and an end face of the inner ring facing the outer side in the axial direction, and a second labyrinth gap between the first sealing member and the shaft are formed.

Abstract: A tolerance ring can include a generally cylindrical body that can include a side wall. The sidewall can define a top and a bottom. Further, the sidewall can include a plurality of wave structures that can extend from the sidewall, a plurality of unformed sections, and a gap that can extend along the entire length of the body. Each unformed section can be located between a pair of adjacent wave structures. Further, the gap can establish a split in the body. The tolerance ring can also include at least one hole intersecting at least one of the wave structures to establish a perforated wave structure.

Abstract: A tolerance ring can include a generally cylindrical body having a sidewall. The sidewall can include a plurality of wave structures extending from the sidewall at regular intervals around the body, a first unformed section between a first pair of adjacent wave structures, and a second unformed section between a second pair of adjacent wave structures. The gap can extend along an entire length, L, of the body to establish a split in the body. The second unformed section can include a slot therein. The slot can have a length, LS, and LS?80% L.

Abstract: A tolerance ring is formed of a plate member, in a ring shape that is substantially circular along a predetermined direction, and provided with a plurality of protrusions projected radially in a circumferential direction, wherein an even number of the protrusions are arranged along the circumferential direction, and a plurality of straight lines that pass through a central portion of the plurality of protrusions and a center of a circle that circumscribes the tolerance ring cross one another.

Abstract: A tolerance ring for a hard disc drive assembly is disclosed and can include a plurality of discrete tolerance ring panels. Each tolerance ring panel can include an arcuate sidewall that can include an unformed portion and at least one projection extending from the arcuate sidewall. The projection can be surrounded by the unformed portion of the arcuate sidewall and the tolerance ring can be configured to be deployed in an interference fit between an inner component and an outer component to provide torque coupling between an inner component and an outer component.

Abstract: In an HDD actuator pivot bearing unit 10, an axial inner surface 22a of a shield cap 22 is formed into a stepped shape so that an axial minimum gap a1 with a shield member 14e of one bearing 14 is narrower than an axial minimum gap a2 with an outer ring 14b and so that an axial minimum gap a3 with a boundary position 14b3 between an axial end face of the outer ring 14 and an annular groove 14b1 is narrower than the axial minimum gap a2 with the outer ring 14. By doing so, the amount of air passing through an interior of the bearing can be reduced to thereby reduce outparticles.

Abstract: A bearing device includes a shaft having an axis, plural rolling bearings arranged at axially separated positions and rotatably supporting the shaft, a first cylindrical member for supporting the rolling bearings therein and having a first screw on a part of an outer surface thereof, a second cylindrical member having a second screw engaging with the first screw on an inner surface thereof and mounted to the outer surface of the first cylindrical member by engaging the first screw with the second screw, a restricting member provided on the outer surface of the second cylindrical member for preventing relative axial movement of the second cylindrical member with respect to the first cylindrical member when a portion of the second member contacts the restricting member.

Abstract: A pivot bearing 13 includes: a shaft 21; and a plurality of ball bearings 20 which are arranged in an axial direction with respect to the shaft 21 and each of which has an inner ring 27 fixed to the shaft 21 and an outer ring 25 fixed to a fixing hole 18 of an arm 16 via a tolerance ring 12, the pivot bearing being configured to swing around the shaft. The number of balls of each ball bearing 20 and the number of concave portions of the tolerance ring 12, which are configured to press the outer ring 25, are relatively prime to each other. Accordingly, it is possible to inexpensively make the reliable pivot bearing that achieves high precision with a simple structure, and thus a reliable high density magnetic recording apparatus is provided.

Abstract: An actuator pivot bearing is disposed at least partially within a pivot bearing bore of a disk drive actuator. The actuator pivot bearing includes a fixed inner bearing shaft having a lower portion that is attached to the disk drive base. It may also have a rotatable outer bearing sleeve that is attached to the actuator body. The actuator pivot bearing also includes an adsorptive element (e.g. comprising activated carbon, silica gel, zeolites) disposed between the fixed inner bearing shaft and an inner surface of the pivot bearing bore. In certain embodiments, the adsorptive element may optionally be disposed within an actuator pivot bearing internal cartridge space. A restricted clearance between the rotating and fixed bearing components may partially block a diffusion path from the pivot bearing lubricant to the read head. The adsorptive element may be disposed adjacent that restricted clearance.

Abstract: A method of assembling a tolerance ring between opposing surfaces of an inner and outer component arranged to mate with one another to provide an interference fit therebetween includes mounting the tolerance ring on one of the inner and outer components whereby the projections are received in a recessed portion on that component, partially mating the inner and outer components, and completing mating by causing relative movement between the tolerance ring and the recessed portion to move the projections from the recessed portion and to be compressed between the mated inner and outer components. The tolerance ring includes an annular band of resilient material for engaging an opposing surface of one of the inner and outer components. The annular band has a plurality of deformable projections extending radially therefrom to engage the opposing surface of the other one of the inner and outer components.

Abstract: An integrated pivot-carriage for a hard-disk drive. The integrated pivot-carriage includes a carriage having a center-bore with an integrated bearing-spacer portion. The integrated pivot-carriage also includes a pivot-shaft configured to provide support for rotation of the carriage. The pivot-shaft is disposed within the center-bore of the carriage. In addition, the integrated pivot-carriage includes at least one raceless ball-bearing that is configured to allow rotation of the carriage about the pivot-shaft. The raceless ball-bearing is disposed between the pivot-shaft and the carriage.

Abstract: A bearing device has a sleeve that encircles a shaft, and two side-by-side roller bearings rotatably support the sleeve coaxially on the shaft. A spacer portion protrudes radially inwardly from the sleeve and extends between the two roller bearings. The sleeve axially overlaps a minor portion of one roller bearing but does not overlap a race surface thereof, and the sleeve axially overlaps a major portion of the other roller bearing including a race surface thereof.

Abstract: A tolerance ring (10) for providing an interference fit between inner and outer components (36, 50) is disclosed. The tolerance ring (10) comprises a deformable band having a plurality of radially extending projections around its circumference, wherein the projections include a set of axially spaced protuberances (12, 13) separated by a unformed region (11) circumferentially adjacent to an axially elongate protuberance (15), the axial extent of which spans the axial extent of the set of axially spaced protuberances. This arrangement of protuberances facilitates the transfer of retention force to a component that is composed of a plurality of independent parts, e.g. two or more bearings (54, 56) separated by a spacer (58).

Abstract: A tolerance ring (10) for providing an interference fit between inner and outer components (36, 50). The tolerance ring (10) comprises a deformable band having a plurality of radially extending projections around its circumference. The projections include a set of axially spaced protuberances (12, 13) separated by an unformed region (11) circumferentially adjacent to an axially elongate protuberance (15), the axial extent of which spans the axial extent of the set of axially spaced protuberances. This arrangement of protuberances facilitates the transfer of retention force to a component that is composed of a plurality of independent parts, e.g. two or more bearings (54, 56) separated by a spacer (58).

Abstract: A thin component such as the actuator arm (10) of a hard disk drive, is mounted on a pivot or pin (31), such as the pivot assembly of the hard disk drive, using a ring (32), e.g. a tolerance ring, having one or more projections (35), wherein the engagement of the component (30) and the ring (32) is such as to apply a force to the component (30) in a direction which is inclined to both the radial and axial directions of the pivot or pin (31). The pivot or pin (31) has a flange onto which the component (30) is pressed by the axial component of the force generated by the ring on the component. The edge of the ring (32) remote from the component (30) is engaged with a stop element, e.g. another flange (34) of the pivot or pin (31).

Abstract: A method is provided for maintaining the aggregate stiffness of a pivot bearing assembly generally employed along with an actuator assembly of a magnetic disk drive, while increasing the stiffness in a predetermined direction. More specifically, bearing cartridges used in conjunction with actuator assemblies of the prior art employ at least one ball bearing assembly positioned about a stationary shaft. A modification is presented herein that generally concerns repositioning and maintaining the balls of the ball bearing along a predetermined axis for efficient reaction of loads.

Abstract: A mounting assembly comprising mating inner and outer components (36, 38) mounted together using a tolerance (20) is disclosed. The tolerance ring (20) has radially extending projections (28) that are configured to cause the tolerance ring (20) to operate into the plastic phase of its compression force/retention force characteristic. This can be achieved by using softer projections than those found in conventional tolerance rings. The force required to mount the tolerance ring and a range of retention forces exhibited by it for a given variance in sizes of mating components is thereby stabilized.

Abstract: An internal support interface which provides vibration and acoustic isolation. A stationary shaft has a medial portion about which a rotatable member rotates. An end portion of the shaft has an annular base surface surrounding a stub shaft projection. A substantially planar housing member has a support post which extends from an annular interior surface in adjacent, non-contacting proximity to the stub shaft projection to form a gap therebetween. An annular damping member mutually contactingly surrounds the stub shaft projection and the support post while being compressed between the base surface of the shaft and the interior surface of the housing member.

Abstract: Embodiments of the present invention help to stabilize a tilt amount of a head gimbal assembly with respect to a magnetic disc. According to one embodiment of the present invention, in a head stack assembly in which a head gimbal assembly, a carriage, and a head gimbal assembly are stacked and fixed by a pivot cartridge, a spring washer and a nut, an annular recess portion having a length in the radial direction of a flange is formed on a contact face of the flange formed at one end of the cartridge, so that two places of a mount plate of the head gimbal assembly may be partially supported in the radial direction of the flange.

Abstract: A head support device of self-balancing type and a disk drive are disclosed. The head support device reduces manufacturing variation in a load and the number of components, and has stability and reliability, while being inexpensive. In this head support device, a flange and a nut cramp, via a collar, a head support arm having a reinforcing plate fixed thereto. The head support arm is supported rotatably about a line provided between contact points at which pivots contact the flange and in a direction perpendicular to a recording medium. A spring as an elastic member provides an urging force toward the recording medium, and is provided unitarily with the head support arm. Bent portions are provided on both sides of the arm composing the head support arm to a tab.

Abstract: A head stack assembly for use in a disk drive is provided that includes an actuator body, a rotary bearing, a sleeve, and a cam member. The actuator body is pivotable about an axis of rotation. The actuator body has an actuator bore that extends along the axis of rotation. The actuator bore includes an actuator bore surface. The sleeve is disposed between the rotary bearing and the actuator body and comprises a first surface that engages the actuator bore surface. The cam member has a second surface eccentric to said first surface. The second surface engages the actuator bore surface.

Abstract: A tolerance ring for coupling an actuator arm to a pivot bearing while maintaining mass eccentricity of the actuator arm. The tolerance ring having a substantially cylindrical base portion with a first radius about a central axis and extending a length parallel to the central axis, the cylindrical base portion has a first tab and a second tab extending along the length of the cylindrical base portion, the first tab being positioned proximate to the second tab. The tolerance ring improves mass eccentricity by radially displacing the first tab at a second radius about the axis such that a radial gap is formed between the first tab and second tab.

Abstract: An ultra-small optical/magnetic head actuator includes: a swing arm movable in a horizontal direction (tracking direction) and a vertical direction (focusing direction) and having mounted thereon a head for reading and writing information on a disk. A tracking actuator moves the swing arm in the horizontal direction (tracking direction) and a pivot hinge adjusts a radius of rotation of the swing arm and guides the movement of the swing arm in the tracking direction. A focusing actuator moves the swing arm in the vertical direction (focusing direction), wherein the focusing actuator includes a focusing coil attached under the swing arm and a Halbach magnet array disposed under the focusing coil minimizes thickness. Friction or backlash can be avoided, and non-repetitive errors can be reduced. The thickness of the ultra-small storage device can be reduced due to the use of a Halbach magnet array.

Abstract: One embodiment of the invention can include a method of assembling an actuator arm system for a hard disk drive. The method can include: placing a lower bearing on a shaft; placing an actuator arm on the lower bearing; placing an upper bearing on the shaft; applying an adhesive between an inner race of the upper bearing and the shaft; applying an axial preload force to the inner race of the upper bearing; curing the adhesive; and releasing the preload force.

Abstract: A snap ring for applications requiring cleanliness has a novel recessed interior contour that reduces debris generation during installation of the snap ring. The snap ring is suitable for applications where a reduction in debris generation is desirable, such as to retain an actuator pivot bearing in information storage devices like magnetic hard disk drives.

Abstract: A method for making a dual actuator pivot, wherein the need for adhesive bonding is eliminated and assembly time is minimized. An upper sleeve assembly includes an upper and lower ball bearing press fitted therein and a lower sleeve assembly includes an upper ball bearing press fitted therein, the first and second sleeve assemblies being press fitted to a shaft having a ball bearing press fitted at the base of the shaft. A predetermined axial load that is tuned to select a desired resonance frequency for the first and second actuator bearing assemblies may be applied during the press fitting of the first and second sleeve assemblies. The shaft may be chilled to shrink the shaft. Alternatively, the components may be heated.

Abstract: Embodiments of the invention position accurately an actuator head suspension assembly (AHSA) relative to a magnetic disk without using any positioning jig, as achieved through a simple structure and involving no increase in manufacturing, and to prevent the AHSA from being charge. In one embodiment, a conductive AHSA includes a pivot opening formed to provide a step at an adjoining portion of two holes having different hole diameters from each other. A pivot bearing assembly includes a first conductive roller bearing and a second conductive roller bearing. The first and the second roller bearings include outer races and inner races with balls interposed between the outer races and the inner races. The first and the second roller bearings are disposed in tandem to achieve the following arrangements.

Abstract: A head stack assembly for a disk drive includes an actuator body. The actuator body includes a pair of sides, a bore defining a longitudinal axis, a first slot extending between the pair of sides, a second slot extending along a direction perpendicular to the longitudinal axis, the second slot extending from the first slot to the bore. The head stack assembly further includes a coil portion cantilevered from the actuator body in one direction and an actuator arm cantilevered from the actuator body in a direction opposite from the coil portion.

Abstract: A tolerance ring for coupling an actuator arm to a pivot bearing while maintaining mass eccentricity of the actuator arm. The tolerance ring having a substantially cylindrical base portion with a first radius about a central axis and extending a length parallel to the central axis, the cylindrical base portion has a first tab and a second tab extending along the length of the cylindrical base portion, the first tab being positioned proximate to the second tab. The tolerance ring improves mass eccentricity by radially displacing the first tab at a second radius about the axis such that a radial gap is formed between the first tab and second tab.

Abstract: A stacked suspension assembly for a data storage drive having, for example, at least two suspension members with each suspension member has a bearing hole therethrough. At least one spacer is positioned between the at least two suspension members to separate adjacent suspension members Each spacer has a bearing hole therethrough. A bearing member can be inserted within the bearing holes of the at least two suspension members and the at least one spacer. The bearing member has an actuator hole into which an actuator pivot member is insertable.

Abstract: A method is provided for maintaining the aggregate stiffness of a pivot bearing assembly generally employed along with an actuator assembly of a magnetic disk drive, while increasing the stiffness in a predetermined direction. More specifically, bearing cartridges used in conjunction with actuator assemblies of the prior art employ at least one ball bearing assembly positioned about a stationary shaft. A modification is presented herein that generally concerns repositioning and maintaining the balls of the ball bearing along a predetermined axis for efficient reaction of loads.

Abstract: An actuator supporting apparatus of a hard disk drive includes a pivot bearing including an inner ring, an outer ring, and a rolling member, which are installed coaxially, to support an actuator arm to pivot. The actuator supporting apparatus also includes a support structure to support upper and lower surfaces of the inner ring, and a buffer member interposed between at least one of the upper and lower surfaces of the inner ring and the support structure, to buffer vibrations and impacts. Thus, a feature of buffering vibrations and impacts by the buffer member is not changed and is constantly maintained, regardless of accumulation of manufacture allowance or a change in the environment. Also, a problem in reliability of a product due to deterioration of structural strength, which occurs in the conventional actuator supporting apparatus, does not occur in the actuator supporting apparatus of the present invention.

Abstract: A pivot assembly for use in a hard disk drive, in which ball bearings are placed at both ends of a shaft, and a spacer is disposed between outer rings of the ball bearings. The spacer is fixed to the outer rings by laser welding.

Abstract: An actuator assembly and method for orienting a head over a disc within a multi-disc servo-track writer incorporates an actuator block, rotational air bearing, translational air bearing, adaptor plate, E-block and actuator arm/head assembly. Rotation of the E-block, and hence actuator arm/head assembly, is directly controlled by the movement of the rotational air bearing, which is rotated by a motor. The air bearing provides for reduced friction and, as a result, decreased eccentricity of the head as compared to related art configurations. A translational air bearing laterally positions the actuator assembly within the multi-disc servo-track writer for servo-track recording.

Abstract: A head supporting device with a loading/unloading mechanism and a disk drive unit using the head supporting device. The head supporting device and a voice coil motor (VCM) make up a head actuator of the drive system. The head actuator has i) a support arm rotatable on a bearing, moving in directions along the radius of a recording medium and vertical to the surface of the medium; ii) a magnetically levitating head on a slider facing the medium; and iii) resilient member for applying force to the arm in a direction close to the medium. The VCM has a pair of yokes, a magnet, and a coil. When the head is lead to a head retracting position, the other end of the arm is pulled by the interaction of a magnetic member and the magnet at the resting position and adjacencies. This eases the load on the VCM, contributing to a compact and slim disk drive unit with toughness and rapid data-access.

Abstract: A disk drive includes a pivot-bearing cartridge configured to pivotally support the head stack assembly on the base of the drive. A tolerance ring is coupled to the pivot-bearing cartridge and includes a single sleeve defining an inner sleeve surface facing the pivot-bearing cartridge and an outer sleeve surface facing away therefrom, and a layer of dampening material disposed on the inner or outer sleeve surfaces so as to be in contact with the pivot-bearing cartridge or the bore surface of the through bore that is defined in the body portion of the head stack assembly, respectively.

Abstract: A pivot assembly that narrows the gap of the seal member as much as possible and can effectively restrain the diffusion of gas and dirt from the inside, and, moreover, can also solve the problem of out gas from a hub cap, is presented. The pivot assembly has ball bearings mated to both ends of a shaft, a spacer mated to a sleeve disposed between both ball bearings at the outer circumferences of these ball bearings, and has a hub cap member that covers the outside end face of the ball bearings at one end of the shaft. The hub cap is laser welded to the outer circumference of the shaft and the inner circumference of the sleeve, and after laser welding, is thin-width cut by a laser along the entire circumference at the radial middle part.

Abstract: An actuator assembly for a disk drive is provided wherein the pivot cartridge is supported within the bore of the actuator with corrugated end rings. The corrugated end rings provide a uniform distribution of forces on the pivot cartridge and effectively reduce vibrations between the pivot cartridge and the body of the actuator.

Abstract: Assemblies in accordance with the present invention can replace cumbersome and potentially contaminating bearing assemblies for rotary actuators. One such assembly comprises a bearing assembly with a threaded base for insertion into a bore, wherein the bore includes threads for engaging the threaded base of the bearing assembly, eliminating the contamination associated with glueing. The bearing assembly is designed such that it can be disconnected from the rotary actuator for rework without damaging or contaminating the rotary actuator or bearing assembly.

Abstract: In a hard disk drive, there are provided a head assembly 13 that drives a magnetic head 33 that reads and writes data on a recording disk, and a flange section that extends toward the periphery on the sleeve 21 of a pivot member 20 that supports this head assembly 13 so that it is free to pivot; and planar sections 41A and 41B are formed on the peripheral surface of this flange section in order to adjust the balance of the center of gravity of the head assembly 13.

Abstract: Methods in accordance with the present invention can eliminate cumbersome and potentially contaminating methods for connecting a bearing assembly with an actuator assembly. One such assembly comprises a bearing assembly with a threaded base for insertion into a bore, wherein the bore includes threads for engaging the threaded base of the bearing assembly, eliminating the contamination associated with such methods as glueing. The bearing assembly is designed such that it can be disconnected from the actuator assembly for rework without damaging or contaminating the actuator assembly or bearing assembly. This description is not intended to be a complete description of, or limit the scope of, the invention. Other features, aspects, and objects of the invention can be obtained from a review of the specification, the figures, and the claims.

Abstract: Apparatus and method for orienting a head over a disc within a multi-disc servo-track writer preferably uses two gas bearings, an adaptor plate, and an actuator assembly including an E-block and arm/head assembly. Rotation of the E-block, and hence actuator arm/head assembly, can be controlled by the movement of a rotational gas bearing, which is rotated by a motor. The gas bearing provides for reduced friction and, as a result, decreased eccentricity of the head as compared to related art configurations. A translational gas bearing can be used for laterally positioning the actuator assembly for servo track recording.

Abstract: A new fixture which is capable of holding an HSA throughout all processes is invented so that Quasi-Static Test can be done before swaging. Handling operations are reduced and rework is made much easier. The invention further provides a process for testing the HSA by means of the fixture.

Abstract: A pivot bearing cartridge for use in a head stack assembly. The pivot bearing cartridge includes a pivot shaft including a shaft body and a shaft distal end. The pivot bearing cartridge further includes a cap disposed about the pivot shaft. The cap includes a cap annular body and a cap closed end. The pivot bearing cartridge further includes a ball bearing set in mechanical communication with the pivot shaft and the cap annular body. The pivot bearing cartridge further includes a central pivot element disposed between and in mechanical communication with the shaft distal end and the cap closed end for facilitating rotation of the cap relative to the pivot shaft.

Abstract: A pivot bearing cartridge for use in a head stack assembly. The pivot bearing cartridge includes a pivot shaft including a shaft body and a shaft distal end. The pivot bearing cartridge further includes a cap disposed about the pivot shaft. The cap includes a cap annular body and a cap closed end. The pivot bearing cartridge further includes a ball bearing set in mechanical communication with the pivot shaft and the cap annular body. The pivot bearing cartridge further includes a central pivot element disposed between and in mechanical communication with the shaft distal end and the cap closed end for facilitating rotation of the cap relative to the pivot shaft.

Abstract: An actuator assembly has a generally flat sheet metal body with upper and lower surfaces and an actuator bore passing therebetween. The actuator bore is sized to receive the bearing cartridge assembly therethrough. A plurality of tabs project inward from an interior surface of the actuator bore, wherein the tabs extend only partially along a depth of the actuator bore between the upper and lower surfaces. The tabs contact the bearing cartridge assembly and secure it within the actuator bore.

Abstract: A pivot bearing cartridge for use in a head stack assembly. The cartridge includes a pivot shaft including a central axis, a shaft body and a shaft distal end. The cartridge includes a pivot sleeve disposed about the pivot shaft. The pivot sleeve includes a pivot sleeve annular body and a pivot sleeve closed end disposed adjacent the shaft distal end. The cartridge includes a ball bearing set disposed between and in mechanical communication with the shaft body and the pivot sleeve annular body. The cartridge includes a shaft magnet element attached to the shaft distal end adjacent the pivot sleeve closed end. The shaft magnet element is sized and configured to apply a magnetic force to the pivot sleeve in a direction along the central axis for pre-loading the ball bearing set.