JPH09167309A - Machining method for magnetic head core member - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a uniform magnetic film on a ground part of an object member by grinding an object face of the object member with non-transferring part of cutting edge abrasive grain of a rotary grinding stone. SOLUTION: By rotating a grinding stone 50 by driving a motor 52 and also operating a moving means 54 in the direction of Z, the motor 52 and the grinding stone 50 are lowered in the direction of Z1. Thus, a tapered part 22a, which is almost V-shaped in section of a grinding part 22, drills vertically into an object member 10. Consequently, a groove 12 coincident with the tapered surface 22a in shape is formed to the object member 10. And, if the rotary side face 23 of the grinding stone, rotating and cutting in the radial direction of the grinding stone 50, grinds an inclined face 14 in the direction of X, the grinding stone is less abraded and the inclined face 14 can be ground in less surface roughness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic head core for grinding a target member of a difficult-to-cut material for a core of a magnetic head and processing the target surface for forming a magnetic film on the target member. The present invention relates to a method of processing a member.

[0002]

2. Description of the Related Art In such a magnetic recording / reproducing apparatus, digital recording in which signals are digitized and recorded in order to improve image quality and the like is being advanced. The high frequency has been made. By the way, as the density and frequency of magnetic recording have increased, magnetic heads used for recording and reproduction are required to have high output at high frequency and low noise. For example,
In a so-called composite type metal-in-gap head in which a metal magnetic film is formed on a ferrite material, which is often used as a magnetic head for a VTR, and is wound, the inductance is large and the output per inductance is reduced, so that a high frequency region is generated. Therefore, it is difficult to sufficiently deal with digital image recording that requires low output, high frequency, and high density. Under such circumstances, so-called thin film magnetic heads, which are manufactured by a thin film forming process, have been studied as high frequency compatible magnetic heads.

A thin film magnetic head is manufactured by forming a coil in a spiral shape on a difficult-to-cut material such as a ceramic substrate by a thin film forming method such as photolithography, and forming a protective film with an oxide such as alumina on the coil. It A magnetic film for forming a magnetic path of a coil may be formed on the target member (ceramic substrate) of the difficult-to-cut material by sputtering, for example. Therefore, improvement of workability of difficult-to-cut materials such as ceramics is required. Conventionally, when grinding such a difficult-to-cut material, use of a hard grindstone of a bond material (bonding material) such as an electroformed grindstone has been studied.
However, when processing ceramics, it is not easy to perform high-speed processing while securing a ground surface roughness similar to that of ferrite.

[0004]

By the way, when grinding difficult-to-cut materials such as ceramics, it is desired to improve the workability of the ceramics to improve the processing accuracy and the processing efficiency. .

A target member (substrate) 1 for a core of a conventional magnetic head for a video tape recorder using ferrite.
As shown in FIG. 14, it is necessary to grind a plurality of grooves 3 by the grindstone 2 in the arrow X direction. The inclined surface 4 of the groove 3 is a surface on which the magnetic film 5 is formed by sputtering or the like. The target member 1 is cut in the longitudinal direction and the lateral direction in a subsequent process, so that a large number of cores 6 are produced. A coil (not shown) is formed on the magnetic film 5 of the core 6 as a thin film.

When the inclined surface 4 is formed on the target member 1, the grindstone 2 shown in FIG. 14 is used. This grindstone 2 has a grinding peripheral surface 7 formed in advance by θ,
By lowering the grindstone 2 in the arrow Z direction, grooving for forming the groove 3 is performed on the target member 1, and the target member 1 is linearly moved in the arrow X direction. The processing speed of the target member 1 in the arrow X direction at this time is, for example, 3
It is performed at 50 to 500 mm / min. On the other hand, when the target member 1 made of ceramics is used, since the workability of the ceramics is poor, the grinding wheel wear of the grindstone 2 progresses when the grinding processing speed is increased, or the so-called plucking of the ceramics. Due to the phenomenon, the processing speed can only be increased to about 100 mm / min.

In order to make the surface roughness of the inclined surface 4 of the ceramic target member 1 equal to the surface roughness of the inclined surface of the ferrite target member 1, it is necessary to make the grindstone grain size smaller. However, since the grinding wheel wear and the peeling phenomenon further occur when the size is reduced in this way, when the target object 1 made of ceramics is ground, a coarser whetstone is compared with the case where the target object 1 made of ferrite is ground. Need to be processed.
For this reason, the roughness of the processed surface of the ceramic target member 1 becomes worse than that of the ferrite target member 1, so that the magnetic film 5 is uniformly sputtered on the inclined surface 4. I will not be able to. This magnetic film constitutes a magnetic path of a coil which will be formed in a later step, and therefore, the characteristics of the magnetic head are deteriorated or the adhesion strength of the magnetic film is reduced, so that the magnetic film is not formed. The problem of peeling occurs.

Therefore, the present invention has been made in order to solve the above-mentioned problems, and it is possible to efficiently process a target member for a core made of a difficult-to-cut material, and a magnetic film is formed on the ground portion of the target member. It is an object of the present invention to provide a method for processing a member for a core of a magnetic head, which is capable of forming uniformly.

[0009]

SUMMARY OF THE INVENTION In the present invention, the above object is achieved by grinding a target member of a difficult-to-cut material for a core of a magnetic head to form a target surface for forming a magnetic film. This is achieved by a method of processing a member for a core of a magnetic head, in which the rotating grindstone is rotated to grind the target surface of the target member at a non-transfer portion of the cutting edge abrasive grains of the rotating grindstone.
In the present invention, with respect to the target member, when processing the target surface for forming the magnetic film, by rotating the rotary grindstone, using the non-transferred part of the cutting edge abrasive grains of the rotary grindstone, the target part Grind the target surface.

As a result, since the cutting edge abrasive grains of the rotary grindstone are not transferred to the target surface of the target member, a smooth target surface can be processed into the target member regardless of the irregularities of the cutting edge abrasive grains. Therefore, a magnetic film can be uniformly formed on this smooth target surface, and the problem of film peeling due to a decrease in film adhesion strength can be solved. Further, since the target surface of the target portion is ground by the non-transferred portion of the cutting edge abrasive grains, the surface roughness of the target surface can be kept good even if high-speed processing is performed, and the grinding processing speed can be increased. . .

[0011]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. Note that the embodiments described below are preferred specific examples of the present invention,
Although various technically preferable limitations are given, the scope of the present invention is not limited to these modes unless otherwise specified to limit the present invention.

FIG. 1 shows an example of a grinding apparatus for carrying out the method for processing a core member of a magnetic head according to the present invention. The core member 10 of the magnetic head is a target member for grinding, and is a flat plate-shaped member as shown in FIG. The target member 10 is made of ceramics, which is a difficult-to-cut material. As the ceramics, for example, MnO—NiO ceramics or the like can be adopted.

The grinding apparatus shown in FIG.
On the other hand, it is a processing apparatus for forming a plurality of grooves 12 as shown in FIG. Each groove 12 has an inclined surface 14 and a vertical surface 16
And a bottom surface 18. The grinding machine shown in FIG.
A table 20, a grinding unit 22, a control unit 24 and the like are provided. The table 20 includes the target member 10 shown in FIG.
The table is tilted at a predetermined cutting angle θ with respect to L and firmly held. The predetermined cutting angle θ is, for example, 45 degrees. The table 20 indicates the target member 10 with an arrow X.
Direction and arrow Y direction. The table 20 includes a rail 26 that faces the Y direction, a rail 28 that faces the X direction, and a holding portion 30. Rail 26
Guides the rail 28 in the direction of the arrow Y. By operating the motor 32 and rotating the feed screw 34, the rail 28 together with the nut 36 meshed with the feed screw 34 is operated.
Can be moved and positioned in the direction of arrow Y.

Further, the rail 28 can linearly move the holding portion 30 in the arrow X direction. That is, by operating the motor 38 and rotating the feed screw 40, the nut 42 meshed with the feed screw 40 moves together with the holding portion 30 in the arrow X direction. The holder 30 detachably holds the target member 10.

The grinding unit 22 includes a grinding wheel 50 and a motor 5
2 and Z-direction moving means 54 and the like. Motor 5
2 is for rotating the grinding wheel 50 in the arrow R direction, and the Z-direction moving means 54 is for the motor 52 and the grinding wheel 5.
0 can be vertically moved and positioned in the arrow Z direction. The control unit 24 controls the operations of the motors 32, 38, 52 and the Z-direction moving means 54 described above.

Next, an example of a grinding process for forming the groove 12 of FIG. 2 on the target member 10 of FIGS. 1 and 2 will be described with reference to FIGS. 1 and 3. The motor 52 of FIG. 1 is operated to rotate the grinding wheel 50, and the Z-direction moving means 54 is operated to lower the motor 52 and the grinding wheel 50 in the arrow Z1 direction. As a result, the tapered portions 22a, 22a having a substantially V-shaped cross section of the grinding portion 22 are cut vertically downward with respect to the target member 10 as shown in FIG. As a result, the groove 12 having a shape matching the tapered portions 22a, 22a is formed on the target member 10 as shown in FIG.

The tapered portions 22a, 22a are formed to have a crossing angle α as shown in FIG. 3, and the crossing angle α is 90 degrees, for example. Therefore, the groove 12
Will be defined by an inclined surface 14, a vertical surface 16 and a bottom surface 18 as shown in FIGS. In detail, the vertical surface 16 is ground by one taper portion 22a, and the bottom surface 18 is ground by the other taper portion 22a. Then, the inclined surface 14 which is important for forming the polishing film in the subsequent step is ground by the rotating side surface 23 of the grinding wheel 50.

When the inclined surface 14 is ground in the direction of arrow X while cutting the grinding wheel 50 in the radial direction while the rotary side surface 23 rotates in this manner, the abrasion of the wheel is reduced and the surface roughness of the inclined surface 14 is reduced. Can be made smaller.
The reason is as follows.

FIG. 4 shows an ordinary flat rotary grinding wheel 1
5 shows an example in which the target member 10 is ground by the peripheral surface 100a of No. 00, and FIG.
3 shows an example in which the target member 10 is ground by 3. FIG.
Each of the abrasive grains 100c forming the peripheral surface 100a of the ordinary grinding wheel 100 is transferred to the target member 10 without changing the profile of each of the abrasive grains 100c while rotating in the arrow R direction with respect to the target member 10. Will grind. Therefore, the ground surface 10a of the target member 10 has a large surface roughness.

On the other hand, as shown in FIG.
When the target member 10 is ground using the rotating side surface 23 of the target and while moving the grinding wheel 100 in the direction of the arrow Z1, the maximum abrasive grain height of the cutting edge abrasive grain 22d to the side of the target member 10 is the maximum. Since the grinding allowance L is obtained, the profile of the other cutting edge abrasive grains 100d is less likely to be transferred to the grinding surface 10e of the target member 10 and is a so-called non-transferred portion.
The surface roughness of 0e is extremely small. For this reason, the inclined surface 14 of FIG. 3 can be ground as a non-transferred portion of the abrasive grains by the rotating side surface 23 of the grinding wheel 50. The grinding wheel 50 of the grinding unit 22 shown in FIG. 1 moves down in the direction of arrow Z1 and the motor 38 is actuated to operate the target member 1
Since 0 moves in the direction of arrow X (direction toward the front of the paper surface of FIG. 1), the groove 12 as shown in FIG. 2 can be formed.

After the first groove 12 is formed, the grinding wheel 50 is once raised, the motor 32 is operated, and
The holding portion 30 and the target member 10 have an arrow Y for a predetermined pitch.
A predetermined pitch is moved in the direction of arrow Y1. As a result, when the above-described operation is repeated, the second groove 12 is formed in parallel with the first groove 12. The third groove 12 in FIG. 2 is the same as the first and second grooves 1 in the same manner.
2 will be formed in parallel. Inclined surface 1 of each groove 12
Since No. 4 is formed by the rotating side surface 23 of the grinding wheel 50 as described above, the surface roughness becomes small and the inclined surface 14
The upper pluck can be minimized. As a result,
Even if the grinding speed of the grinding wheel 50 is increased, the surface roughness of the inclined surface can be kept good.

Next, please refer to FIG. 6 and FIG. FIG. 6 shows an example of the surface roughness of the inclined surface when the inclined surface of 45 degrees is inclined with respect to the conventional ferrite target member. Further, FIG. 7 shows an example of the measurement result of the surface roughness of the inclined surface when the inclined surface of 45 degrees is formed with respect to the ceramic target member 10 of the present invention. FIG.
Is compared with the surface roughness when a conventional ferrite target member is ground when the ceramic target member 10 is ground on the rotating side surface 23 of the grinding wheel 50. In the example of grinding the target member made of ceramics in FIG. 7, the grindstone grain size is changed several times, and moreover, a straight grindstone (plane grindstone)
And surface roughness in the case of using the grinding wheel 2 having the conventional grinding peripheral surface 7 as shown in FIG.

As a grinding condition, the target member made of ceramics is MnO—NiO ceramics, whereas the conventional target member made of ferrite is MnZn single crystal ferrite. The grindstone used is an electroformed grindstone #
4000, # 3000, # 2500, # 2000, # 1
It is a grindstone of 500 and # 800. The peripheral speed of the grindstone is 500
0m / min, processing speed of target material is 250mm
/ Min, and the cut amount is 0.15 mm.

Referring to FIG. 7, although the surface roughness of the ceramic target member by the # 800 straight grindstone is worse than the surface roughness of the ferrite target member of FIG. Is better than ferrite surface roughness.
By using the above, it was found that the inclined surface can be processed with a surface roughness equal to or higher than that in the case of grinding ferrite. On the other hand, when the conventional 45-degree correction grindstone (grinding grindstone 2 in FIG. 14) is used, the surface roughness deteriorates as the grain size becomes coarser, and it has been found that only # 2500 or more can be used. The reason for this is that the protrusion of the abrasive grains is not entirely transferred to the processed surface on the side surface of the grindstone, as described above, and thus is less affected by the abrasive grain size (see FIG. 5). Target surface 1 at the grinding surface 7
This is because, when is ground, the protrusion amount of each abrasive grain is entirely transferred to the processed surface, and the surface roughness of the inclined surface 4 is affected by the grain size.

Based on these results, the processing method of the present invention uses a grinding wheel 50 as shown in FIGS. 1 and 3,
Moreover, the rotating side surface 23 grinds the inclined surface 14. Then, the target member 10 that is the substrate is tilted at a predetermined angle θ (for example, 45 degrees), and the electroformed grindstone # 1500.
With the above, the grinding wheel 5 having the intersection angle α (for example, 90 degrees)
0 is used to grind the inclined surface 14. As a result,
Even if a grinding wheel 50 with a coarser grain size is used, the inclined surface 1
The surface roughness of No. 4 is not deteriorated and the workability is improved. The grinding process which has been conventionally performed at the processing speed of 100 mm / min with the grinding wheel of electroformed # 2500 is 250 mm / min in the processing method of the present invention. Even if the above is performed, the surface roughness of the inclined surface 14 of the target member 10 made of ceramics is the same as the surface roughness of the inclined surface of the conventional target member made of ferrite. Moreover, it has been confirmed that there is no problem of progress of abrasion of the grindstone on the ceramic target member 10 and peeling of the inclined surface 14.

FIG. 8 shows another example of the processing method of the present invention. In the processing method of FIG. 8, after using a straight type grinding wheel (flat type grinding wheel) 150, the grinding wheel 150 is used again, and as a result, the inclined surface 14 and the vertical surface 16 as shown in FIG. And a groove having a bottom surface 18 is formed. The grinding wheel 150 is also an electroformed wheel and uses # 1500. First, as shown in FIG. 8 (A), the target member 10 made of ceramics is held while being inclined at a predetermined angle θ (45 degrees), and the first groove is ground by the grinding wheel 150 in the same manner as in FIG. While rotating in the R direction, it descends in the Z1 direction to form the first groove 12a. As a result, the rotating side surface 123 of the grinding wheel 150 becomes the inclined surface 14
To form

Next, as shown in FIG. 8B, the target member 10
Is set to 0 degree, that is, the target member 10 is fixed horizontally, and the second groove 12b is formed in the arrow Z1 direction while further rotating the grinding wheel 150. As a result, the groove 12 having the inclined surface 14, the vertical surface 16 and the bottom surface 18 can be formed. In the processing method of FIG. 8, the predetermined groove 12 is formed by cutting the grinding wheel 150, which is a straight grinding wheel, twice into the target member 10. That is, since the groove 12 is finally formed by using the grinding wheel 150 twice, the amount of grinding processing for each time is reduced, so that the processing speed is 500 m, for example.
It was confirmed that it could be further increased to m / min.

Further, a grinding wheel 150 which is a flat type rotary wheel.
Grinding wheel 1
It has also been confirmed that the target member 10 can be processed immediately after 50 dressings. Further, in this processing method, since the second groove 12b does not serve as the head sliding surface, it is not necessary to make the surface roughness equal to the inclined surface of the target member made of ferrite. Of course you can raise it.

Next, another processing method of the present invention shown in FIG. 9 will be described. In the processing method of FIG. 9, the target member 10 is also held while being inclined at the predetermined angle θ (45 degrees).
First, in the first stage, the straight grinding wheel 150 is cut in the target member 10 in the Z1 direction. As a result, the first groove 12a is formed, and the inclined surface 14 is formed by the rotating side surface 123. Next, while the target member 10 is also held while being inclined at a predetermined angle θ,
The second groove 12b is formed by using the grinding wheel 50 of. However, since the rotating side surface 23 of the grinding wheel 50 does not need to grind the side surface 123 which is already formed with a predetermined surface roughness, the second groove 12b is formed with a slight shift as shown by the broken line. That is, it is necessary to prevent the rotating side surface 23 of the grinding wheel 50 from contacting the inclined surface 14.

As described above, in the embodiment of the processing method of the present invention, the target member 10 which is the work of FIG. 1 is tilted at a predetermined angle, for example, 45 degrees with respect to the horizontal plane, and the rotating side surface of the grinding wheel 50 is rotated. The inclined surface 14 is formed at 23. The inclined surface 14 is a surface for sputtering a magnetic film in a later step, and even if the surface roughness of the inclined surface is the ceramic target member 10, the conventional ferrite target member 1 is used.
Although it is necessary to machine the surface roughness with a quality equal to or higher than that of the inclined surface of 0, the machining method of the present invention can achieve that, and high-speed machining is possible.

Further, as shown in FIG. 8, the first groove 12a is formed with the inclined surface 14 by using the straight type grinding wheel 150, and has the same surface roughness as the inclined surface of the conventional ferrite target member 10. Then, the target member 10 is set horizontally again to form the second groove 12b using the same straight grinding wheel 150. Since the groove 12 can be finally formed by such a double-cut grinding process, the grinding wheel 15
It is not necessary to correct the angle of 0 itself, and since the second groove 12b is not particularly related to the inclined surface 14, high-speed processing can be performed.

Therefore, the effect is exerted when a core member (target member) made of a difficult-to-cut material such as ceramics is processed, and the inclined surface on which the magnetic film needs to be sputtered is the side surface of the grinding wheel. By processing with, it is possible to simultaneously improve the processing efficiency by increasing the processing speed and improve the head characteristics by improving the roughness of the processed surface. The target member 10 in which a plurality of grooves 12 are formed as shown in FIG. 2 corresponds to a groove processing required in a later step, a step of fusing or cutting glass, and the inclined surface 14 of the groove of FIG. By forming the coil in this way, a chip of the magnetic head as shown in FIG. 13 can be obtained. here,
An example of the post process will be described. FIG. 10 shows a groove processing step and a glass fusing step which are subsequent steps.
(A) shows a state in which a plurality of grooves 12 having inclined surfaces 14 and the like are formed on the target member 10. FIG.
FIG. 10B shows a state in which the magnetic film 107 and the like are formed on the inclined surfaces 14 and the like of these grooves, and FIG. 10C shows a groove 110 for forming a thin film coil and a magnetic path. 2 shows a state in which the groove 111 for removing the unnecessary magnetic film portion is formed orthogonally to the groove 12. The magnetic film 107 on the inclined surface 14 is a portion necessary for forming a magnetic path for a thin film coil, and the surface roughness of the inclined surface 14 has another vertical surface 16 defining the groove 12 and a bottom surface 18. (See Figure 2).

Next, as shown in FIG. 10D, each groove is filled with glass 112 to form a groove 113 for regulating the track groove as shown in FIG. 10E. As shown in FIG. 10F, the groove 113 is filled with the glass 117, the surface is flattened, and the thin film coil is formed in the etched depression 114 in FIG. 10G. FIG. 11A shows a gap film sputtered, and FIG. 11B shows a groove 440 for separating terminals.
Insert The target members 10 and 10 of FIG. 12 obtained by processing in this manner are attached face to face, and
13 along the cutting line CCL of FIG.
The magnetic head chip can be obtained.

The chip of the magnetic head shown in FIG. 13 can record a signal on or reproduce a signal from a video tape of a video tape recorder. The present invention is not limited to the above embodiment. The magnetic head obtained by the processing method of the present invention is not limited to a video tape recorder, but can be applied to a method of processing a member for a core of a magnetic head of another information recording device such as a digital audio tape recorder (DAT). it can.

[0035]

As described above, according to the present invention,
This is done in order to solve the problem, and the target member for the core made of the difficult-to-cut material can be efficiently processed, and the magnetic film can be uniformly formed on the ground portion of the target member.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a grinding apparatus for realizing a method of processing a core member of a magnetic head according to the present invention.

FIG. 2 is a view showing a state in which a groove is formed on a target member of the grinding apparatus of FIG.

FIG. 3 is a diagram showing a manner of securing a groove for a target member.

FIG. 4 is a diagram showing a state in which the profile of the abrasive grains of the grinding wheel is transferred to the object by the object being ground by the peripheral surface of the conventional grinding wheel.

FIG. 5 is a view showing a manner of grinding an inclined surface using the grinding wheel of the present invention.

FIG. 6 is a view showing an example of surface roughness of a conventional ferrite inclined surface.

FIG. 7 is a diagram showing an example of surface roughness in the processing method of the present invention.

FIG. 8 is a diagram showing another embodiment of a method for processing a core member of a magnetic head according to the present invention.

FIG. 9 is a diagram showing still another embodiment of a method of processing a member for a core of a magnetic head of the present invention.

FIG. 10 is a diagram showing an example of a processing procedure after performing the processing method of the present invention.

11 is a view showing a continuation of the processing shown in FIG.

FIG. 12 is a diagram showing a state in which one half body and another half body are stacked.

FIG. 13 is a diagram showing an example of a chip of the obtained magnetic head.

FIG. 14 is a diagram showing a conventional processing method.

[Explanation of symbols]

 10 Target Member 10e Grinding Surface (Non-Transfer Part, Slope) 14 Slope (Target Surface) 22d Cutting Edge Grain 50 Grinding Wheel (Rotating Wheel) θ (Predetermined Angle, Cutting Angle)

Claims (7)

[Claims] 1. When a target member of a hard-to-cut material for a core of a magnetic head is ground and a target surface for forming a magnetic film is processed into this target member, a rotary grindstone is rotated to rotate the grindstone. A method for processing a member for a core of a magnetic head, which comprises grinding a target surface of a target member at a non-transferred portion of the cutting edge abrasive grains. 2. The rotary grindstone is a flat grindstone, the non-transferred portion of the cutting edge abrasive grains is the rotating side surface of the rotary grindstone, and the cutting direction of the rotary grindstone is the radial direction of the rotary grindstone. 1. A method for processing a member for a core of a magnetic head according to 1. 3. The method of processing a member for a core of a magnetic head according to claim 1, wherein the magnetic film is a magnetic thin film formed by sputtering. 4. The method of processing a member for a core of a magnetic head according to claim 2, wherein a taper portion is provided in the vicinity of the rotating peripheral surface of the rotary grindstone. 5. The method of processing a member for a core of a magnetic head according to claim 4, wherein the radial direction of the rotary grindstone and the arrangement direction of the target member are inclined by a predetermined cutting angle. 6. When a target member of a hard-to-cut material for a core of a magnetic head is ground and a target surface for forming a magnetic film is processed into this target member, the radial direction of a flat type rotary grindstone is changed. With respect to the arrangement direction of the target member, the target surface is ground by the rotation side surface of this flat type rotary grindstone by inclining by a predetermined cutting angle, and then the radial direction of the rotary grindstone having the taper portion is set to the target member. A method for processing a member for a core of a magnetic head, characterized by arranging in a direction orthogonal to an arranging direction and grinding a portion in the vicinity of a target surface with a rotary grindstone having this taper portion. 7. The method for processing a member for core of a magnetic head according to claim 6, wherein the predetermined cutting angle is 45 degrees.