JP2000199523A - Manufacture of dynamic pressure fluid bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a machining method for grooves of an accurate dynamic pressure fluid bearing by forming discontinued grooves for a dynamic pressure bearing in the external peripheral surface of a shaft without producing pitch displacement. SOLUTION: In forming fluid holding groove 2 on the external peripheral surface 1A of a radial bearing 1, groove-shaped sections 17 (17a and 17b) for forming fluid holding grooves in at least one of a pair of transfer rollers 11 and 12 so that the total number 2N of the peak K of the groove-shaped sections 17 becomes equal to the number 2N of the fluid holding grooves, and the fluid holding grooves formed in the peripheral surface 1A of the radial bearing 1 are formed by pressing the groove-shaped sections 17 against the external peripheral surface 1A of the radial bearing 1 while rotating the radial bearing 1 between the transfer rollers 11 and 12.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a hydrodynamic bearing in which a fluid retaining groove for a hydrodynamic bearing is formed discontinuously on the outer peripheral surface of a shaft.

[0002]

2. Description of the Related Art Conventionally, in a hydrodynamic bearing in the radial direction, a method for forming a fluid holding groove for holding a lubricating fluid on the outer peripheral surface of a shaft in order to improve the slip between the peripheral surfaces has been proposed. For example, a forming method by pressing disclosed in JP-A-63-280914 is known. In order to solve the problem that a uniform groove cannot be obtained by simple press working, a pair of hard rollers each having a pattern formed thereon is pressed with the work shaft interposed therebetween, and the roller pattern is pressed. Is transferred to As other processing methods, methods such as laser processing, shot blast processing, and etching processing are known.

[0003]

However, laser processing,
Processing methods such as shot blast processing and etching processing require expensive processing equipment, have complicated processing steps, and have a problem that the processing unit price increases.

[0004] In order to reduce the processing unit price, cutting and rolling with a hard ball can be considered, but in these processings, since the tool is always in contact with the shaft, a discontinuous groove is formed on the outer peripheral surface of the shaft. It is not possible. In order to solve this problem, it is conceivable to obtain a discontinuous groove by removing a part of the shaft by cutting or grinding after the continuous groove processing, but the amount of bearing fluid (mainly oil) increases or There are drawbacks in that the shaft size becomes complicated due to two types of shaft dimensions, and the cost is rather increased.

On the other hand, Japanese Unexamined Patent Publication No. Sho 63-280914 discloses
In the method using roller rolling and flat die rolling disclosed in Japanese Patent Application Publication No. H10-284, a discontinuous groove can be efficiently processed by a simple process, but in the case of a shallow groove having a groove depth of about 10 μm, the groove pitch is small. There was a disadvantage that it shifted. This is because in conventional processing using roller rolling and flat die rolling, a large number of grooves are cut in the rollers and dies, and the shaft to be processed is rotated several times until the processing is completed. Since the projection of the rolling tool hits the groove several times thereafter, if the groove depth is as shallow as about 10 μm, there is a slip between the rolling tool and the shaft immediately after the start of rolling of the shaft. Easy to occur, 1 axis
Since the position where the convex portion of the rolling tool comes into contact again after the rotation is shifted from the groove position formed immediately after the start of the rolling, a pitch error occurs on the shaft.

Conventionally, in order to solve this problem, a plurality of steps of forming a groove of a predetermined depth by forming a groove deeply to about 30 μm at the time of rolling and performing post-processing including swelling after the subsequent groove processing. However, there is a problem that the cost is high. In particular, since a shaft with a flange or the like cannot be efficiently post-processed (through-feed centerless grinding), it is difficult to employ a rolling process when a shallow groove is required in this type of shaft shape.

Further, among the workpieces, there is a workpiece whose axis is located at the center of the cylindrical flange portion and whose cylindrical surface is covered. In such a case, a direction perpendicular to the axis is used. It is not possible to apply tools or light from
There is a problem that only the processing of applying a tool from a direction horizontal to the axis can be adopted, and the discontinuous surface cannot be processed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-precision and high-performance hydrodynamic bearing by forming discontinuous hydrodynamic bearing grooves on the outer peripheral surface of a shaft without causing a pitch shift. And a method of manufacturing a hydrodynamic bearing.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a feature of the present invention is to provide a method of manufacturing a hydrodynamic bearing which receives a shaft in a radial direction with respect to a shaft. A groove for forming the fluid holding groove is formed so that the total number of the ridges of the groove is equal to the number of grooves of the fluid holding groove, and the work is performed between the pair of rollers or dies. The point is that the groove-shaped portion is pressed against the outer peripheral surface of the shaft to be processed while rotating the shaft, so that the required fluid holding groove is formed on the outer peripheral surface.

A groove portion for forming a groove necessary for holding the fluid is provided on at least one of the pair of rollers or the dies, and the total number of the ridges of the groove portion is a groove of the required fluid holding groove. Since the number is equal to the number, when the grooved portion is pressed against the outer peripheral surface of the shaft to be processed while rotating the shaft to be processed between a pair of rollers or dies, it is formed once by the convex portion of the grooved portion. Since the chevron is not pressed again into the formed groove, the pitch of the formed groove does not shift.

The groove portion required to form the fluid holding groove may be entirely formed on one roller or die. However, the necessary groove portion is divided into two parts, and these are divided into a pair. The roller and the die may be provided separately.

According to a configuration in which a groove-shaped portion necessary for forming a fluid holding groove is formed on one roller or die, and the remaining rollers or dies are flat rollers or flat dies, Alternatively, the bulge of the groove formed by the die can be crushed by a flat roller or a flat die to form a smooth outer peripheral surface with a groove without the need for special post-processing.

According to the present invention, also in a method of manufacturing a hydrodynamic bearing which receives a shaft surrounded by a flange portion in a radial direction, a tip portion has a space between the collar portion and the shaft. A pair of dice members formed so as to be able to enter the inside are prepared, and at least one of the tip ends of the pair of dice members is provided with a groove-shaped portion for forming a required fluid holding groove, the groove-shaped portion. Are formed so that the total number of the ridges is equal to the number of the fluid holding grooves, and presses the grooved portion against the outer peripheral surface of the shaft while rotating the shaft between the distal ends, and A method is proposed in which a fluid holding groove is formed on the outer peripheral surface.

According to the proposed method, even if the shaft on which the fluid holding groove is to be formed is surrounded by the collar portion and machining from the horizontal direction is impossible, the same as in the previous case. Thus, the fluid holding groove can be formed without a pitch shift.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 shows a fluid holding groove forming apparatus 1 for forming a discontinuous fluid holding groove necessary for realizing a fluid dynamic bearing on the outer peripheral surface of a shaft to be processed by the method of the present invention.
It is a perspective view showing an example of an embodiment of zero.

In the present embodiment, the fluid retaining groove forming device 10 forms a substantially rectangular discontinuous groove on the bearing outer peripheral surface 1A of the radial bearing 1 used as the rotating shaft of the hard disk drive motor in the circumferential direction. It is configured as a device for aligning and forming.

In the fluid holding groove forming apparatus 10, a pair of transfer rollers 11, 12 which are hard rotating bodies as transfer rollers are rotatably mounted on corresponding support blocks 13, 14 by shafts 15, 16 respectively. . Transfer roller 11,
12 are formed on the outer peripheral surfaces 11A, 12A of the radial bearing 1 of the radial bearing 1 which is a shaft to be processed. The necessary groove 17 is formed.

In this embodiment, the groove 17 has a first groove 17A formed on a part of the outer peripheral surface 11A and a second groove 17 formed on a part of the outer peripheral surface 12A. And a mold portion 17B. The first groove-shaped portion 17A is made up of N substantially K-shaped chevrons, while the second grooved portion 17B is also made up of N-shaped substantially K-shaped chevrons K.

The shafts 15 and 16 are disposed in parallel, so that the outer peripheral surface 11A of the transfer roller 11 and the outer peripheral surface 12A of the transfer roller 12 face each other while being kept parallel, and the support blocks 13 and 14 are provided. Is moved along the directions indicated by arrows X and Y by a driving mechanism (not shown),
The transfer roller 11 and the transfer roller 12 can be approached and separated from each other while maintaining the parallel state.

As described above, the transfer rollers 11 and 12 are rotatably supported by the support blocks 13 and 14 constituting the pressing mechanism, and the pressing mechanism moves as indicated by arrows X and Y in the figure. The radial bearing 1 is sandwiched between the outer peripheral surfaces 11A and 12A of the transfer rollers 11 and 12 by bringing the transfer rollers 11 and 12 closer to each other.
1A and 12A are configured to be pressed against the outer peripheral surface 1A of the bearing. In this state, the transfer rollers 11 and 12 are rotated to transfer the groove patterns of the first grooved portion 17A and the second grooved portion 17B to the bearing outer peripheral surface 1A of the radial bearing 1. .

In this embodiment, the center of the outer peripheral surface 11A of the transfer roller 11 and the center of the outer peripheral surface 12A of the transfer roller 12 are located between the outer peripheral surface 11A of the transfer roller 11 and the outer peripheral surface 12A of the transfer roller 12. A support table 18 for mounting the radial bearing 1 is provided so as to be parallel to the axes of the shaft 15 of the transfer roller 11 and the shaft 16 of the transfer roller 12, and the radial bearing 1 is always mounted on the outer peripheral surfaces 11A and 12A. It is configured to be arranged at the contact position.

Next, the fluid holding groove forming apparatus 1 shown in FIG.
Referring to FIG. 2, a specific example of a procedure for forming the fluid holding groove 2 on the outer peripheral surface 1A of the radial bearing 1 by using the method of the present invention will be described with reference to FIG.

The radial bearing 1 is placed on a support 18 with a large space between the transfer roller 11 and the transfer roller 12.
, And the transfer roller 11 and the transfer roller 12 are brought into a rotation stop state. In this state, the support blocks 13 and 14 are moved in the directions of arrows X and Y (see FIG. 1). Thereby, the radial bearing 1 is pressed and sandwiched between the outer peripheral surface 11A and the outer peripheral surface 12A. At this time, the transfer roller 11 that rotates in the direction of the arrow U is the first roller on the outer peripheral surface 11A.
While the one end 17Aa of the grooved portion 17A slightly contacts the bearing outer peripheral surface 1A of the radial bearing 1, the transfer roller 12, which rotates in the direction of arrow V, has the outer peripheral surface 12A.
One end 17Ba of the upper second grooved portion 17B is positioned so as to slightly contact the bearing outer peripheral surface 1A of the radial bearing 1. In this state, the transfer rollers 11 and 1
2 are synchronously rotated in the above-described predetermined directions U and V. As a result, the groove pattern of the first grooved portion 17A is transferred to a half circumferential portion of the bearing outer peripheral surface 1A of the radial bearing 1, and
A second groove 17 is formed on the remaining half of the outer peripheral surface 1A of the bearing.
The groove pattern of B can be transferred. In the embodiment shown in FIG. 2, the first and second grooved portions 17A, 17B
Have six rows (12 pieces) each, so that
12 rows (24 pieces) on the outer peripheral surface 1A of the radial bearing 1
Is formed.

As can be seen from FIG. 2, the first channel portion 17A
The other end 17Ab and the other end 17 of the second grooved portion 17B
Since the ends of Bb are flat surfaces 11Aa and 12Aa, respectively, the first and second grooved portions 17A and 17B provide the radial bearing 1 with a rotation of half a rotation or more necessary for forming a groove. The bulge of the peripheral edge of the fluid holding groove 2 formed on the outer peripheral surface 1A of the bearing is pressed and crushed by the flat surfaces 11Aa and 12Aa having no irregularities, thereby preventing the roundness of the portion from deteriorating and finishing to a uniform diameter. This eliminates the need for the step of removing (grinding or cutting) the protruding portion after the pressing step, thus making it possible to reduce the number of steps.

As described above, the first and second grooved portions 17
Since the total number of the ridges K of the grooved portion 17 composed of A and 17B is set to be equal to the total number of the fluid holding grooves 2 to be formed on the bearing outer peripheral surface 1A of the radial bearing 1, The ridge of the groove portion 17 is not pressed again against the groove once formed on the outer peripheral surface 1A. For this reason, since the pitch shift of the groove, which has been conventionally considered as a problem, does not occur, even if the depth of the fluid holding groove 2 is shallow, the required fluid holding groove can be formed in the radial bearing 1 by one machining. It can be formed on the outer peripheral surface 1A of the bearing.

In the embodiment shown in FIG. 1, the case where the number of grooves to be formed on the bearing outer peripheral surface 1A is an even number is shown, but the number may be an odd number. In this case, the number is appropriately allocated so that the total number of the number of the ridges of the first grooved portion 17A and the number of the ridges of the second grooved portion 17B becomes a required number. That is, the number of peaks of the first grooved portion 17A and the second
The total number of the groove-shaped portions 17B and the number of the mountain-shaped portions 17B is the bearing outer peripheral surface 1A
The allocation can be performed appropriately so as to be equal to the total number of the fluid holding grooves 2 to be formed thereon.

Therefore, for example, as shown in FIG.
The groove portion 17 having the number of peaks required only for the transfer roller 12
And the transfer roller 11 may be a flat roller. Also in this case, it is possible to solve both the problem of the pitch shift due to the double pressing and the problem of the post-processing for removing the swelling of the peripheral edge of the groove.

FIG. 4 shows another embodiment of the present invention. The fluid holding groove forming device 20 shown in FIG. 4 uses a pair of transfer dies 21 and 22 instead of a pair of rollers, and the die surfaces 21A and 22A of the transfer dies 21 and 22.
The first and second grooved portions 17A and 17B shown in FIG.
Are formed on the bearing outer peripheral surface 1A of the radial bearing 1 by using the grooved portion 23 composed of the first and second grooved portions 23A and 23B. The required fluid holding grooves 2 are formed by transfer.

In the case of the fluid holding groove forming apparatus 20 shown in FIG. 4, the radial bearing 1 provided between the transfer dies 21 and 22 is transferred to the transfer dies 21 and 22 as shown in FIG.
And press the transfer dies 21, 22 with arrows P, Q
Are moved in opposite directions and in parallel to each other, so that the first groove 23
The groove pattern of A is transferred, and the groove pattern of the second grooved portion 23B is transferred to the remaining half of the outer peripheral surface 1A of the bearing, in the same manner as in the fluid holding groove forming apparatus 10 of FIG. The required fluid holding groove can be satisfactorily formed on the bearing outer peripheral surface 1A of the radial bearing 1 without causing a pitch shift.

FIG. 6 shows a modification of the fluid holding groove forming device 20 shown in FIG. 4. In the fluid holding groove forming device 20 'shown in FIG. 6, the transfer die 21 is a flat die, and It is different from the fluid holding groove forming apparatus 20 only in that all the groove portions 23 are formed in the die 22. According to the fluid holding groove forming device 20 ', the required fluid holding groove is formed by the groove type portion 23 formed on the transfer die 22 on the bearing outer peripheral surface 1A by one rotation of the radial bearing 1,
At the same time, the transfer die 21 can crush the ridge of the groove formed by the transfer.

FIG. 7 is a front view of a fluid holding groove forming apparatus 30 for forming a discontinuous fluid holding groove on the outer peripheral surface of a shaft with a collar according to the method of the present invention, and FIG. FIG.
Is a perspective view of a collar shaft to be processed, and FIG. 10 is a sectional view thereof.

The flanged shaft 5 is formed by integrally extending a brim portion 5C from the base portion 5A around a shaft portion 5B suspended from the base portion 5A. Fluid is provided on the outer peripheral surface 5Ba of the shaft portion 5B. In order to form the holding groove, the collar shaft 5 is set in the fluid holding groove forming device 30 as shown in FIGS.

The fluid holding groove forming device 30 has a pair of dies 31 and 32 and a holding mechanism 33 for rotatably supporting the flanged shaft 5. The holding mechanism 33 is composed of one end holding member 34 and the other end holding member 35, and the flanged shaft 5 is formed by a conical pointed end 34A of the one end holding member 34 and a conical pointed end 35A of the other end holding member 35 from the front and rear. It is held so as to be pressed, and thereby is rotatably held between the one end holding member 34 and the other end holding member 35.

The tip of the die 31 has a hanging portion 3 which can enter a space 5D between the shaft portion 5B and the flange portion 5C.
1A is formed. Similarly, the tip of the die 32 is formed with a hanging portion 32A that can enter the space 5D between the shaft portion 5B and the flange portion 5C. Hanging part 3
Outer end surface 31Aa of 1A and outer end surface 32Aa of hanging portion 32A
Is formed with a groove-shaped portion 36 necessary to form the fluid holding groove 2 composed of 2N discontinuous, V-shaped grooves to be formed on the outer peripheral surface 5Ba of the shaft portion 5B.

As shown in detail in FIG.
6, in the present embodiment, comprises a first grooved portion 36A formed on a part of the outer end surface 31Aa, and a second grooved portion 36B formed on a part of the outer end surface 32Aa. ing.
The first groove portion 36A is composed of six substantially K-shaped chevrons K, while the second groove portion 36B is also composed of six substantially C-shaped crests K.

The base 31B of the die 31 is attached to a corresponding drive block 37, and the die 31 can be rotated in the direction of arrow R by a drive mechanism (not shown). On the other hand, the base 32B of the die 32 is attached to a corresponding drive block 38, and the die 32 can be rotated in the direction of arrow S by a drive mechanism (not shown). Here, the drive blocks 37, 3
Reference numeral 8 denotes a configuration in which the drooping portions 31A and 32A of the dies 31 and 32 can approach and separate from each other by a driving mechanism (not shown).

Therefore, the hanging parts 31A and 32A are inserted into the space 5D, and the outer end faces 31Aa and 32Aa are used to form the shaft 5A.
B is sandwiched by applying a predetermined pressure, and the first and second grooved portions 36A and 36B are rotated by rotating the dies 31 and 32 in the directions of arrows R and S, thereby rotating the shaft 5B.
And the groove pattern of the groove portion 36 can be transferred to the outer peripheral surface 5Ba of the shaft portion 5B.

Next, the fluid holding groove forming device 3 shown in FIG.
Referring to FIG. 11, a specific example of a procedure for forming a fluid holding groove 5E on the bearing outer peripheral surface 5Ba of the radial bearing 5B by using the method of the present invention will be described with reference to FIG.

The radial bearing 5B is rotatably held by the one end holding member 34 and the other end holding member 35 in a state where the distance between the die 31 and the die 32 is large.
And the die 32 is brought into a rotation stop state. In this state, the dies 31, 32 are brought closer to each other. Thus, the radial bearing 5B is connected to the outer end surface 31Aa of the hanging portion 31A and the hanging portion 3A.
2a is sandwiched between the outer end surfaces 32Aa and pressed. At this time, the die 31 that rotates in the direction of the arrow R is in a state where one end 36Aa of the first grooved portion 36A on the outer end surface 31Aa slightly contacts the bearing outer peripheral surface 5Ba of the radial bearing 5B, The dies 32 to be rotated in the direction of arrow S are positioned so that one end 36Ba of the second grooved portion 36B on the outer peripheral surface 32Aa slightly contacts the bearing outer peripheral surface 5Ba of the radial bearing 5B. In this state, the dies 31 and 32 are synchronously rotated in the above-mentioned predetermined directions R and S, respectively, whereby the groove pattern of the first grooved portion 36A is formed on a half-peripheral portion of the bearing outer peripheral surface 5Ba of the radial bearing 5B. And the groove pattern of the second grooved portion 36B can be transferred to the remaining half of the bearing outer peripheral surface 5Ba. In the embodiment shown in FIG. 11, the first and second groove portions 36A and 36B each have a mountain shape of 6
(12 pieces), and therefore, 12 rows (24 pieces) of fluid holding grooves 5 are provided on the bearing outer peripheral surface 5Ba of the radial bearing 5B.
E is formed.

According to the fluid holding groove forming apparatus 30, the fluid holding groove can be easily formed also on the outer peripheral surface of the shaft surrounded by the collar. According to this method, each of the ridges of the groove portion 36 is provided with only the minimum number necessary for forming the fluid holding groove, so that the ridge is pressed again into the transferred and once formed groove. There is no. For this reason, no pitch shift occurs, and post-processing is not required even in the case of forming a shallow groove. Therefore, even in the case of a shaft with a collar that cannot be post-processed, there is no problem with the formation of the fluid holding groove. The formation can be performed efficiently.

Therefore, a computer hard disk drive, VTR, video camera, digital copy,
Since a dynamic pressure bearing used for a precision motor used in a printer or the like can be processed with high accuracy and high efficiency, a high-performance, low-cost dynamic pressure bearing can be provided. And since it is not necessary to make the groove depth deeper than necessary, the advantage that the tool life is extended can be obtained.

[0043]

According to the present invention, as described above, since the groove pitch shift which occurs in the case of the conventional rolling roller and die tool does not occur, the dynamic pressure with high accuracy can be obtained without post-processing. A bearing groove can be obtained. Therefore, when forming a fluid holding groove having a shallow groove depth, a step of once forming a groove deeper than a required groove depth and then performing cutting to obtain a predetermined groove depth becomes unnecessary. In addition, the life of the tool is extended and the cost is reduced. Further, since post-processing is not required, it is possible to efficiently process the hydrodynamic bearing groove on the flanged shaft which has conventionally been difficult to mass-produce. Similarly, a shaft surrounded by a cylindrical surface that cannot be rolled can be efficiently processed by rolling without affecting the shaft shape.

As another effect, by providing a pressing portion after the groove rolling, even if a bulge occurs around the groove after the groove is formed, the ridge is removed by pressing the ridge with the pressing portion. can do.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a fluid holding groove forming device for performing a method of the present invention.

FIG. 2 is a diagram for explaining a specific example of a procedure for forming a fluid holding groove on a bearing outer peripheral surface of a radial bearing using the fluid holding groove forming device shown in FIG. 1;

FIG. 3 is a view showing a modification of the fluid holding groove forming apparatus shown in FIG. 1;

FIG. 4 is a perspective view showing another embodiment of the fluid holding groove forming device for performing the method of the present invention.

5 is a view for explaining a specific example of a procedure for forming a fluid holding groove using the fluid holding groove forming apparatus shown in FIG. 4;

FIG. 6 is a view showing a modification of the fluid holding groove forming device shown in FIG. 4;

FIG. 7 is a front view showing an embodiment of a fluid holding groove forming apparatus for forming a discontinuous fluid holding groove on the outer peripheral surface of a flanged shaft by the method of the present invention.

FIG. 8 is a plan view of the fluid holding groove forming device shown in FIG. 7;

9 is a perspective view of a flanged shaft that is processed by the fluid holding groove forming device shown in FIG. 7;

FIG. 10 is a cross-sectional view of the flanged shaft shown in FIG. 9;

FIG. 11 is a diagram for explaining a specific example of a procedure for forming a fluid holding groove on a collar with a collar using the fluid holding groove forming device shown in FIG. 7;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radial bearing 1A Bearing outer peripheral surface 2 Fluid holding groove 5 Shaft with collar 10, 20, 20 ', 30 Fluid holding groove forming apparatus 11, 12 Transfer roller 11A, 12A Outer peripheral surface 17, 23, 36 Groove part 21, 22 Transfer Dice 21A, 22A Dice surface 31, 32 Dice 31A, 32A Hanging part

Claims (8)

[Claims] 1. A method of manufacturing a hydrodynamic bearing which receives a radial direction with respect to a shaft, wherein at least one of a pair of rollers or a die is provided with a groove-shaped portion for forming a required fluid retaining groove. Are formed so that the total number of the ridges is equal to the number of the fluid holding grooves, and the outer peripheral surface of the processed shaft is formed by rotating the processed shaft between the pair of rollers or dies. Wherein the required fluid holding groove is formed in the outer peripheral surface. 2. The groove-shaped portion comprises a first groove-shaped portion formed on one of the pair of rollers or dies and a second groove-shaped portion formed on the other of the pair of rollers or dies. A method for manufacturing a hydrodynamic bearing according to claim 1. 3. The method for manufacturing a hydrodynamic bearing according to claim 2, wherein the number of each of the first and second groove-shaped portions is equal. 4. The dynamic pressure according to claim 1, wherein the groove portion is formed only on one of the pair of rollers or dies, and the other of the pair of rollers or dies is a flat roller or a flat die. Manufacturing method of fluid bearing. 5. A method for manufacturing a hydrodynamic bearing which receives a shaft surrounded by a collar portion in a radial direction with respect to the shaft, wherein a tip portion can enter a space between the collar portion and the shaft. A pair of die members formed as described above is prepared, and at least one of the tip portions of the pair of die members is provided with a groove-shaped portion for forming a required fluid holding groove, and the total number of the ridges of the groove-shaped portion. Is formed so as to be equal to the number of the fluid holding grooves, and presses the groove-shaped portion against the outer peripheral surface of the shaft while rotating the shaft between the tip portions, thereby forming the required fluid holding groove into the outer periphery. A method for manufacturing a hydrodynamic bearing, characterized in that it is formed on a surface. 6. The groove-shaped part comprises a first groove-shaped part formed on one of the pair of dies and a second groove-shaped part formed on the other of the pair of dies. Method of manufacturing a hydrodynamic bearing. 7. The method of manufacturing a hydrodynamic bearing according to claim 6, wherein the first and second groove portions have the same number of ridges. 8. The method of manufacturing a hydrodynamic bearing according to claim 5, wherein the groove-shaped portion is formed only on one of the pair of dies, and the other of the pair of dies is a flat die.