JP2001325781A - Magnetic disk cartridge and method for manufacturing its center core - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely form a center core of a magnetic disk cartridge constituted by rotatably housing magnetic disk media into a flat cartridge case and fixing the center core having a spindle hole to be inserted with a spindle of a drive assembly at its center to the central position of the magnetic disk media. SOLUTION: A plate member is preformed with tapered and recessed parts 62 and 62d respectively at both surfaces 62a and 62b in the central segment by pressing the plate member from both surfaces by forging in the state of allowing a thin part 62e to remain in the central part of the thickness direction of the central segment and thereafter the thin part 62e is subjected to working to scrape off the thin part to a cylindrical shape from a spindle insertion direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-small magnetic disk cartridge having a disk-shaped magnetic disk medium accommodated in a flat cartridge case and having a large recording capacity, and fixed to the center of the magnetic disk medium. The present invention relates to a method for manufacturing a center core.

[0002]

2. Description of the Related Art Conventionally, a magnetic disk medium (a so-called floppy disk) in which a magnetic layer is provided on both sides of a disk-shaped base made of a flexible polyester sheet or the like and magnetically recorded on the magnetic layer by a magnetic head while being driven to rotate. (Registered trademark) disk) is provided in a flat case, and is mainly used as a recording medium for a computer because of its advantages such as easy handling and low cost.

[0003] In such a magnetic disk cartridge, the magnetic disk medium is located at the center thereof.
The drive device is fixed to a center core having a spindle hole into which a spindle is inserted.
A hole is formed so that the bottom surface of the center core faces the outside and the spindle of the drive device can be chucked with respect to the center core. Conventionally, the center core is generally formed by drawing a metal plate.

By the way, the miniaturization of the computer using the above-mentioned magnetic disk cartridge has progressed, and the notebook type personal computer has become widespread. An external system without a built-in disk drive device is now being sold. The adoption of this external method is excellent in terms of portability of small personal computers.However, for example, there is a problem that a large amount of data cannot be recorded and reproduced because magnetic disk cartridges cannot be used at the carrying destination of small personal computers. This causes a problem that data cannot be recorded on a plurality of magnetic disk cartridges.

[0005] From these points, some small personal computers have a PC card slot (conforming to the PCMCIA specification) in which a PC card is mounted to support an external interface and additional memory. It has been proposed to configure an external storage device using a magnetic disk cartridge.

A PC that can be inserted into the PC card slot
The specifications of the card are type II, the thickness is 5.0 mm, and the magnetic disk cartridge and the disk drive are intended to be included in this thickness. Therefore, the thickness of the magnetic disk cartridge is about 2 to 3 mm. It must be made ultra-thin.

[0007] Even when the above-mentioned ultra-small magnetic disk cartridge is constructed, a large recording capacity is required as a recording medium. In order to secure a maximum recording capacity by performing high-density recording, the transfer rate must be increased. Therefore, it is necessary to rotate the magnetic disk medium at high speed.

[0008]

Therefore, high precision is required for the center core of a large-capacity ultra-small magnetic disk cartridge. In particular, the inner peripheral surface of the spindle hole is as parallel as possible to the outer peripheral surface of the spindle. In order to obtain a desirable chucking compatibility with the drive device, it is necessary to finish a portion parallel to the outer peripheral surface of the spindle with high precision.

However, when the center core is of the conventional drawing type, it is formed by deep drawing, so that the spindle hole may be tapered. For this reason, the taper structure was canceled by pressing again from the opposite side of the drawing side, and an attempt was made to secure an effective straight portion.However, since the press was restricted from the side opposite to the drawing side, the reference surface was rather changed. There are many adverse effects such as loss of verticality with the spindle hole.

On the other hand, in order to improve the surface accuracy and the like, it is preferable to form the center core by cutting, but there is a possibility that the magnetic properties may be deteriorated by cutting the material. In a floppy disk, the center core is chucked to the spindle mainly by a magnetic attraction method. Therefore, it is not preferable that the magnetic property of the material is deteriorated by the cutting process. From the point of inviting, cutting is not preferable.

In addition, when the magnetic disk cartridge is chucked in the drive device, at the initial stage when the spindle is inserted into the spindle hole from the bottom of the cartridge, the cartridge surface is not perpendicular to the axis of the spindle but slightly inclined. Therefore, since the axis of the spindle is not parallel to the axis of the spindle hole, there is a problem that the spindle is not smoothly inserted into the spindle hole.

In view of such circumstances, an object of the present invention is to provide a large-capacity ultra-small magnetic disk cartridge having a center core which overcomes the above-mentioned problems, and a method of manufacturing the center core.

[0013]

According to the present invention, a magnetic disk medium is rotatably housed in a flat cartridge case, and a center core having a center of a spindle hole into which a spindle of a drive device is inserted is provided. In the magnetic disk cartridge fixed at the center position of the center core, the inner wall surface of the spindle hole of the center core has a cylindrical wall surface occupying the center in the axial direction of the spindle hole, and axial lines extending from both ends of the cylindrical wall surface. And an inclined wall portion whose diameter is increased outward in the direction.

The inclination angle of the inclined wall portion with respect to the axis of the spindle hole is such that when the magnetic disk cartridge is chucked in a drive device, the inclination angle is changed from the initial stage when the spindle is inserted into the spindle hole from the bottom surface of the cartridge. Preferably, it is equal to or greater than the movement angle of the cartridge until it is king.

Further, according to the present invention, a magnetic disk medium is rotatably accommodated in a flat cartridge case, and a center core having a center of a spindle hole into which a spindle of a drive device is inserted is provided at a center position of the magnetic disk medium. A method of manufacturing a center core in a fixed magnetic disk cartridge, wherein a plate member is pressed from both sides by forging to leave a thin portion at the center in the thickness direction of the center portion. Then, tapered recesses are formed on both surfaces of the thin film, and then the thin portion is subjected to a process of pulling out the cylindrical shape from the spindle insertion direction to complete the spindle hole.

[0016]

According to the magnetic disk cartridge of the present invention, the inner wall surface of the spindle hole of the center core has a cylindrical wall surface having a wall surface parallel to the axis at the center of the spindle hole in the axial direction. By this, a high-precision fitting state with respect to the spindle is obtained, and the cartridge is provided in the drive device by providing the inclined wall portions whose diameters are expanded outward in the axial direction from both ends of the cylindrical wall portion. When mounted, there is an advantage that the spindle is easily inserted into the spindle hole even if the axis of the center core is inclined with respect to the axis of the spindle.

Further, according to the method for manufacturing a center core of the present invention, the center core is formed by forging, so that a high-accuracy center core can be produced at a low cost without the risk of deterioration in magnetic properties as in cutting. .

Further, the thin wall portion formed by forging is subjected to a process of pulling out a cylindrical shape from the insertion direction of the spindle to form a cylindrical wall surface portion of the spindle hole. Can be pierced.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.

FIG. 1 is a perspective view of an embodiment of a magnetic disk cartridge according to the present invention, showing a state in which a window for inserting a magnetic head is closed by a shutter member, as viewed from above. FIG. 2 is a perspective view of a state in which the magnetic head insertion window is opened as viewed from the lower surface side. FIG. 3 is an exploded perspective view of the magnetic disk cartridge. Further, FIG. 4A is an enlarged sectional view of a central portion, and FIG.
(B) is an enlarged sectional view of the center of the center core. In addition, in order to clarify the structure, the thickness and the like of each part in the drawings are shown in proportions different from actual dimensions.

The magnetic disk cartridge 1 has a disk-shaped magnetic disk medium 10 (see FIG. 3) rotatably housed in a flat cartridge case C.
The cartridge case C includes a base plate 2 serving as a central member.
And a substantially planar upper cover case 3 and a lower cover case 4 attached to the top and bottom of the base plate 2. The magnetic disk medium 10 has a disk-shaped base made of a flexible polyester sheet or the like provided with magnetic layers on both sides, and has a metal center core 11 fixedly integrated at the center.

The base plate 2 of the cartridge case C
The annular portion 66 of the center core 11 (FIG. 4)
(A)) is provided, and the lower cover case 4 is provided with a hole 2 at a position overlapping the hole 27.
A hole 7 having a size substantially equal to 7 is formed, and the bottom surface of the annular portion 66 of the center core 11 faces the outside from the hole 7.
The magnetic disk medium 10 is housed in a cartridge case C.

A window 8 is formed at the front end of the cartridge case C with respect to the insertion direction D (arrow in FIG. 1) with respect to the drive device so that the recording / reproducing magnetic head can be accessed. The window 8 is vertically penetrated and opened from the front end faces of the base plate 2 and the upper and lower cover cases 3 and 4 toward the center thereof in a rectangular shape (see FIG. 2). A shutter member 5 for opening and closing the portion 8 is built inside the upper and lower cover cases 3 and 4 so as to be slidable in the left-right direction.

With such a structure of the window 8, the recording / reproducing magnetic head can be inserted into the window 8 from the front end face side of the cartridge case C without opening and closing greatly.
Moreover, the adoption of the built-in shutter member 5 prevents the shutter member 5 from coming off due to insufficient strength due to miniaturization, becomes strong against dropping, etc., and has good assemblability.

Next, the structure of each component will be specifically described with reference to FIG.

First, the base plate 2 is formed of a synthetic resin such as an acrylonitrile-butadiene-styrene copolymer (ABS resin) or a POM resin, and has a substantially rectangular flat plate shape. A circular recess 21 for accommodating the disk medium 10 is formed, and a circular hub accommodation hole 27 is opened at the center of the thin bottom plate of the recess 21. In addition, the front end portion of the bottom plate of the concave portion 21 is cut into a substantially rectangular shape, and the shutter member 5
Space 2 into which a lower plate 52 to be described later is movably inserted.
2, the central portion of the front end portion of the base plate 2 is removed in the front-rear direction, and the window portion 8 is opened vertically. The front surface of the front wall on one side (the right side in FIG. 3) of the window 8 of the base plate 2 is on the other side (the left side in FIG. 3).
A spring housing 23 is formed to retreat from the front surface of the front wall, and a shutter spring 6 described later is arranged in this portion.

The corners 25 of the four corners of the base plate 2 are formed so as to protrude in the vertical direction, have a large thickness, and protrude outward. The four corners of the upper and lower cover cases 3 and 4 correspond to the corners. When the upper and lower cover cases 3 and 4 are fitted to the base plate 2, the corner portions 25 of the base plate 2 are exposed to the outside. Each corner portion 25 is provided in a shape in which the surface protrudes flush or outward with the surface of the upper and lower cover cases 3 and 4.

By exposing the corner portion 25 of the base plate 2 to the outside in this way, when a shock or the like at the time of a drop acts, the corner portion 25 can absorb the shock, and can be inserted into the drive device and inserted. At the time of unloading operation, it is prevented from getting stuck and stable operation is ensured. In each corner 25, a hole 26 penetrating in the vertical direction (a hole having an intermediate depth without penetrating) may be used.
Is provided so as to obtain a larger buffering action at the time of a drop impact. The base plate 2 has a strength that allows a deformation that does not hinder the recording and reproduction of the magnetic disk medium 10. However, from the viewpoint of shock absorption, the base plate 2 is preferably made of an elastic plastic. In addition, a material containing a lubricant is preferable in terms of sliding with respect to the shutter member 5, and a material containing a filler material is used in order to improve dimensional accuracy and improve assemblability with the cover cases 3 and 4. Is good.

A notch-shaped concave portion 15 is formed on the side surface of the corner portion 25 on both sides of the front portion of the base plate 2 as shown in FIG. 1, and this concave portion 15 is used for positioning when mounted in the drive device. Alternatively, it is provided to prevent erroneous insertion in the front-back direction or the front-back direction. The recess 15 may be provided only on one side surface or on the side surface of the rear corner portion 25. In the case of the present embodiment, the corner of one of the front corners 25 is notched diagonally to form the erroneous insertion prevention part 16.

Further, on the side of the cartridge case C,
At a position different from the concave portion 15, for example, as shown in FIG. 1, an identification portion 17 for disc type (for example, type of recording capacity) is provided on the side wall portions of the cover cases 3 and 4 near the rear corner portion 25. Is provided, but a write protector section may be provided here. Furthermore, the identification section 17 may be provided with an identification piece that enables the detection function to be turned on / off so as to be able to be inserted or inserted / extracted. By forming the concave portion 15 and the identification portion 17 on the side surface, a drive-side detection mechanism or the like having no installation space in the vertical direction can be arranged on the side.

The upper and lower cover cases 3 and 4 are formed of a high-strength material such as a pressed stainless steel plate. The upper cover case 3 and the lower cover case 4 have a substantially symmetrical shape, and the four corners are rectangular. It is removed, a flat rectangular window 8 is opened in the center of the front part, and the front, rear, left and right edges are bent at right angles, and the front walls 31, 41, both side walls 32, 42, respectively.
The rear wall portions 33 and 43 are configured. The front wall portion 3 on one side (the left side in FIGS. 1 and 3 and the right side in FIG. 2) with respect to the window portion 8.
The slits 18 (see FIG. 1) are formed between the upper and lower front wall portions 31 and 41 when the upper and lower cover cases 3 and 4 are attached to the base plate 2. It has become. The shutter opening / closing member on the drive device side is inserted into the slit 18 and moves along the slit 18 to open the shutter member 5. The front walls 31 and 4 on the opposite side of the window 8 (the right side in FIGS. 1 and 3 and the left side in FIG. 2).
1, that is, a notch is formed at the end side of the portion located in front of the spring storage portion 23, and the upper and lower cover cases 3,
A rectangular spring insertion opening 19 (see FIGS. 1 and 2) is formed in a state where the front wall portions 31 and 41 of the shutter 4 are fitted together, and is used for mounting the shutter spring 6.

On the upper surface of the central portion of the upper cover case 3,
A concave portion 35 serving as a label attaching portion is formed, and a bottom surface of the concave portion 35 projects downward. The recess 35 is provided in the rotation area of the magnetic disk medium 10 in an assembled state. The depth of the concave portion 35 is set at the center of the space between the lower surface of the concave portion 35 facing the bottom surface of the circular concave portion 21 of the base plate 2 and the bottom surface of the circular concave portion 21 in the thickness direction of the base plate 2. 10 is set to be located. That is, the magnetic disk medium 1 located at the center in the thickness direction of the base plate 2
0 so that the upper and lower clearances are substantially equal.
By setting the depth, the rotational stability of the magnetic disk medium 10 is improved, and the presence of the concave portion 35 improves the strength of the upper cover case 3.

The shutter member 5 is inserted between the base plate 2 and the upper and lower cover cases 3 and 4 and into a sliding space 22 opened in the base plate 2 on the lower surface side, and is slidably mounted in the left and right opening and closing directions. You. The shutter member 5 is made of metal, for example, formed in a substantially U-shaped cross section from a stainless steel plate or an aluminum plate. The upper plate portion 51 and the lower plate portion 52 are connected by a connecting portion 53 at the front end. The height of 53 is substantially equal to the thickness of the front part of the base plate 2. Then, a shutter window 54 is formed by being cut out in a substantially rectangular shape from the connecting portion 53 to the upper surface plate portion 51 and the lower surface plate portion 52. The shutter window 54 has a size substantially corresponding to the window 8 of the cartridge case C, and is communicated with the shutter window 54 during the opening operation. The shutter window 54 is provided at a position deviated from the center of the shutter member 5, and together with the connecting portion 53, the cartridge case C
A closing area for closing the window 8 is formed adjacent to the shutter window 54.

A spring receiving projection 55 bent from the connecting portion 53 of the shutter member 5 is provided on the inner surface of the front end of the shutter window portion 54 on the closed area side, and the shutter spring 6 formed by a coil spring in the opening and closing direction is provided on the back thereof. When contracted, the shutter member 5 is urged in the closing direction. Although not shown, at least one of the upper surface plate portion 51 and the lower surface plate portion 52 is cut and raised, and is engaged with a guide groove extending in the left and right direction on the base plate 2 so as to be assembled. It is useful for preventing the coming off. Reinforcing ribs 56 are formed on the upper plate portion 51 and the lower plate portion 52 of the shutter member 5 to prevent deformation during the opening operation. The reinforcing rib 56 is formed in a protruding shape protruding outward to suppress the generation of abrasion powder and the like due to the sliding of the tips of the upper and lower plate portions 51 and 52 contacting the upper and lower cover cases 3 and 4. It also has the effect of reducing the frictional resistance of the device and ensuring the stability of the opening and closing operation.

Above and below the magnetic disk medium 10, a protective sheet 12 made of a plastic sheet or the like having a PET sheet surface subjected to slip processing (Teflon (registered trademark) processing) is interposed. The protective sheet 12 has a portion corresponding to the window portion 8 removed in the radial direction to form a substantially C-shape, and an opening 12a is formed in a portion opposite to the window portion 8, and a cleaning member 13 is provided in this portion. The cleaning member 1 is fixed to the inner surface of the upper cover case 3 and the bottom surface of the base plate 2 from the magnetic disk medium 10 side.
At the same time, the protection sheet 12 is fixed by the fixation of the protective sheet 3.
The cleaning member 13 is brushed on the side facing the magnetic disk medium 10 and comes into contact with the surface of the magnetic disk medium 10 to remove dust on the surface. An adhesive is applied to the opposite surface of the cleaning member 13.

To assemble the magnetic disk cartridge 1, the protective sheet 12 is fixed to the circular concave portion 21 of the base plate 2 and the lower surface of the upper cover case 3 in advance by fixing the cleaning member 13 to the circular concave portion 21 of the base plate 2. After the magnetic disk medium 10 is set in the shutter member 5, the shutter member 5 is mounted from the front. Subsequently, the upper cover case 3 is fitted to the base plate 2 from above and the lower cover case 4 is fitted and held from below to form an integral unit. 4 is spot-welded. As a result, the upper surface of the circular recess 21 of the base plate 2 is covered with the upper cover case 3, and the flat space defined by the bottom surface of the upper cover case 3 and the upper surface of the circular recess 21 becomes a storage space for the magnetic disk medium 10. The magnetic disk medium 10 is rotatably stored. Thereafter, the coil-shaped shutter spring 6 is bent from the spring insertion port 19 in the front wall portion of the upper and lower cover cases 3 and 4 while the inner spring housing 2 is being bent.
3 and the front end thereof is brought into contact with the spring receiving projection 55 of the shutter member 5, and the rear end is pressed into the storage portion 23 while being contracted, thereby completing the assembly. In addition, the spring insertion port 1
9, the shutter spring 6 assembled
Is locked out.

When the magnetic disk cartridge 1 is loaded in the drive device, the pawl of the opening / closing mechanism is inserted into the slit 18 at the front end, engages with the end of the shutter member 5, and moves it in the opening direction. Manipulate. Accordingly, the window 8 of the base plate 2 is opened, and the hub receiving hole 27 of the base plate 2 is opened.
The bottom of 1 is exposed to the outside through the hole 7 of the lower cover case,
The state shown in FIG. 2 is obtained.

As shown in FIG. 4 (a), the center core 11 has a disc-shaped portion 62 provided at the center with a spindle hole 61 penetrating between the parallel upper and lower surfaces 62a and 62b, and a periphery of the disc-shaped portion 62. , Annular portions 65 and 66 formed coaxially with the spindle hole 61 and a flange 67 having an upper surface with an attachment surface 67a of the magnetic disk medium 10.
It is composed of The spindle 70 of the drive device has a small cylindrical portion 7 inserted into the spindle hole 61 of the center core 11 at the center of the flat upper surface 70a.
1 is coaxially provided, and the lower surface 62b of the disc-shaped portion 62 of the center core 11 is magnetically attracted to the flat upper surface 70a.

The inner wall surface of the spindle hole 61 is shown in FIG.
As shown in the figure, a cylindrical wall surface portion 61a occupying a central portion of the spindle hole 61 in the direction of the axis L, and diameters are expanded from upper and lower ends of the cylindrical wall surface portion 61a toward upper and lower surfaces 62a and 62b, respectively. inclined wall portion 61b which is inclined by an angle theta ₁ with respect to L, consisting of 61c. The cylindrical wall surface portion 61a of the spindle hole 61 is parallel to the outer wall surface 71b of the cylindrical small diameter portion 71 of the center core 11, and its axis L
The dimension in the direction is set in the range of 0.3 to 0.6 mm.

Further, the inclined wall portion 61b, the inclination angle theta ₁ of 61c, as shown in FIG. 5, the spindle when the magnetic disk cartridge 1 is chucked by the drive device, the spindle 70 from the bottom surface of the cartridge 1 is set to the moving angle theta ₂ equal to or greater than the cartridge from the initial stage to be inserted into the hole 61 until the chucking (θ ₁ ≧ θ _2). By setting the inclined wall portion 61b, the inclination angle theta ₁ of 61c in this way, reliable chucking is ensured.

Next, a method of manufacturing the center core 11 having the above configuration will be described with reference to FIG.

First, the plate member is pressed from both sides by forging to form a disk-shaped portion 62, annular portions 65 and 66, and a flange 67, and a central portion corresponding to the spindle hole 61 of the disk-shaped portion 62. In addition, this disc-shaped portion 62
The tapered recesses 62 are respectively formed on the upper and lower surfaces 62a and 62b in such a manner that the thin portion 62e is left in the center in the thickness direction of
By forming c and 62d coaxially, FIG.
Inclined wall portions 61b and 61c of the spindle hole 61 at
Is formed in advance.

Next, the thin wall portion 62e is subjected to a process of pulling out the cylindrical shape from the spindle insertion direction indicated by the arrow, thereby forming a cylindrical wall surface portion 61a of the spindle hole 61 in FIG. 4B. The spindle hole 61 is completed.

As is clear from the above description, in the present embodiment, the inner wall surface of the spindle hole 61 of the center core 11 has a wall surface parallel to the axis L at the center of the spindle hole 61 in the direction of the axis L. By providing the cylindrical wall portion 61a, a highly accurate fitting state with respect to the spindle 70 is obtained, and the inclined wall surface whose diameter is increased outward from the upper and lower ends of the cylindrical wall portion 61a in the axial direction L. Since the cartridges 1 are provided with the portions 61b and 61c, even when the axis of the center core 11 is inclined with respect to the axis of the cartridge 1 when the cartridge 1 is mounted on the drive device, the small-diameter portion 71 of the spindle 70 There is an advantage that it can be inserted into the hole 61 without difficulty.

Further, since the center core 11 is formed by forging, a high-accuracy center core 11 can be manufactured at low cost without the risk of deterioration of magnetic properties as in cutting.

Further, the thin portion 62 formed by forging
The cylindrical wall portion 61a of the spindle hole 61 is formed by subjecting e to a process of pulling out the cylindrical shape from the insertion direction of the spindle 70, so that the spindle hole 61 can be drilled with high precision.

[Brief description of the drawings]

FIG. 1 is a perspective view of an embodiment of a magnetic disk cartridge according to the present invention, showing a state where a window for inserting a magnetic head is closed by a shutter member, as viewed from above.

FIG. 2 is a perspective view of the magnetic disk cartridge shown in FIG. 1, showing a state in which a window for inserting a magnetic head is opened, as viewed from a lower surface side;

FIG. 3 is an exploded perspective view of the magnetic disk cartridge shown in FIGS. 1 and 2;

FIG. 4A is an enlarged sectional view of a main part of a magnetic disk cartridge, and FIG. 4B is an enlarged sectional view of a central portion of a center core.

FIG. 5 is an explanatory diagram showing a state in which a magnetic disk cartridge is mounted on a drive device.

FIG. 6 is an explanatory view of a method for manufacturing a center core according to the present invention

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetic disk cartridge C cartridge case 2 Base plate 3 Upper cover case 4 Lower cover case 5 Shutter member 6 Shutter spring 8 Magnetic head insertion window 10 Magnetic disk media 11 Center core 12 Protective sheet 13 Cleaning member 19 Spring insertion opening 21 Circular recess 23 Spring storage part 25 Corner part 35 Recess 61 Center spindle hole 61a Cylindrical wall part 61b, 61c Slant wall part of spindle hole 62 Center core disk part 62c, 62d Tapered concave part 62e Thin part

Claims (2)

[Claims] A magnetic disk medium is rotatably housed in a flat cartridge case, and a center core having a spindle hole into which a spindle of a drive device is inserted is fixed at a center position of the magnetic disk medium. In the magnetic disk cartridge, the inner wall surface of the spindle hole of the center core has a cylindrical wall portion occupying the central portion in the axial direction of the spindle hole, and the diameter of the inner wall surface is increased outward from both ends of the cylindrical wall surface. A magnetic disk cartridge comprising: an inclined wall portion. 2. A magnetic disk medium is rotatably accommodated in a flat cartridge case, and a center core having a spindle hole into which a spindle of a drive device is inserted is fixed at a center position of the magnetic disk medium. A method of manufacturing the center core in a magnetic disk cartridge, comprising: pressing a plate member from both sides by forging to leave a thin portion at a central portion in a thickness direction of the center portion on both sides of the center portion. A method of manufacturing a center core, wherein a tapered recess is formed in advance, and then the thin portion is subjected to a process of pulling out the cylindrical portion from the spindle insertion direction to complete the spindle hole.