WO2025154332A1 - Golf shaft and method for manufacturing same - Google Patents

Abstract

Provided is a golf shaft capable of obtaining an appropriate yield regardless of the user. The present invention comprises a hollow tubular tube body 3 having a tapered outer surface with an outer diameter gradually increasing between a distal-end part 5 and a proximal-end part 7, the tube body 3 comprising a thin part 11 having a relatively small wall thickness by a change in the inner diameter between the distal-end part 5 and the proximal-end part 7, and thick parts 13 positioned on both sides in the axial direction of the thin part 11 and relatively large in wall thickness, and the thin part 11 being provided in a circular shape and having an inner diameter larger than a corresponding part of a basic shape 15 comprising line segments connecting the inner diameter and the outer diameter of the distal-end part 5 and the inner diameter and the outer diameter of the proximal-end part 7.

Description

Golf shaft and manufacturing method thereof

The present invention relates to a golf shaft and a method for manufacturing the same.

It is known that golf clubs can improve the distance and stability of a ball by utilizing the flexibility of the shaft (hereafter referred to as the golf shaft) during a swing.

For example, Patent Document 1 discloses a golf shaft that can bend appropriately and increase the flight distance of the ball by setting the vibration frequency, weight, and kick point position.

However, the golf shaft in Patent Document 1 is designed to provide an appropriate flex only when the user is at a certain level or above, making it difficult for some users to obtain the appropriate flex.

JP 2023-63540 A

The problem it is trying to solve is the difficulty some users have in obtaining the appropriate flex.

The present invention provides a golf shaft with a hollow tube having a tapered outer surface in which the outer diameter gradually increases between the tip and base ends. Between the tip and base ends, the tube has a thin-walled portion with a relatively small thickness due to the change in inner diameter, and thick-walled portions located on both sides of the thin-walled portion in the axial direction and with a relatively large thickness.

The present invention also provides a method for manufacturing a golf shaft, in which a prepreg is wound around the surface of a mandrel while positioning radial protrusions, and the prepreg is cured to form a hollow tube. The tube has a thin-walled portion with a relatively small thickness between the tip and base ends in a portion corresponding to the protrusion, and has thick-walled portions with a relatively large thickness on both axial sides of the thin-walled portion.

The present invention makes it possible to create a golf shaft that provides appropriate flex for any user.

FIG. 1 is a schematic vertical cross-sectional view of a golf shaft according to an embodiment of the present invention. FIG. 2 is a cross-sectional view taken along line II-II of FIG. 3A and 3B are schematic diagrams showing the bending and return of a golf shaft, with FIG. 3A being an example and FIG. 3B being a comparative example. FIG. 4 is a cross-sectional view showing the crushing of a thin-walled portion of the golf shaft of FIG. FIG. 5 is a graph showing the degree of crushing of the thin-walled portion of the golf shaft of FIG. FIG. 6A is a schematic diagram showing a method for measuring the degree of crushing, and FIG. 6B is a graph showing the measurement results of the degree of crushing. 7A and 7B are graphs showing the results of test shots by different users. FIG. 8 is a graph showing ideal values of the dynamic angle and the attack angle. 9(A) to (C) are vertical cross-sectional views showing a manufacturing method of golf shaft 1, in which FIG. 9(A) shows a mandrel, FIG. 9(B) shows the state in which prepreg has been wound around the mandrel of FIG. 9(A), and FIG. 9(C) shows the state in which tape has been wound around the prepreg of FIG. 9(B). FIG. 10 is a development view showing an example of the prepreg of FIG.

The goal of creating a golf shaft that allows appropriate flex for any user was achieved by providing a thin section in the middle of the golf shaft.

The golf shaft 1 comprises a hollow tube-shaped body 3 having a tapered outer surface with the outer diameter gradually increasing between the tip end 5 and the base end 7. Between the tip end 5 and the base end 7, the tube body 3 comprises a thin-walled section 11 and a thick-walled section 13 due to the change in the inner diameter. The thin-walled section 11 has a relatively small thickness. The thick-walled sections 13 are located on both sides of the thin-walled section 11 in the axial direction and have a relatively large thickness.

The thin-walled portion 11 may be provided in a circumferential manner or partially in the circumferential direction.

It is preferable that the thin-walled portion 11 has an inner diameter larger than the basic shape 15 including the line segment connecting the inner diameter of the tip portion 5 and the inner diameter of the base portion 7.

The length of the tube body 3 can be set, for example, in the range of 838 mm to 1194 mm. The position of the thin-walled portion 11 can be changed depending on the user's head speed, swing habits, etc., but it is preferable that when the length of the tube body 3 is 838 mm, the length from the tip 3a of the tube body 3 is in the range of 150 mm to 688 mm, and when the length of the tube body 3 is 1194 mm, the length from the tip 3a of the tube body 3 is in the range of 150 mm to 1044 mm.

The thick portion 13 may have an inner diameter smaller than the basic shape 15.

The material of the tube body 3 of the golf shaft 1 can be any suitable material, but it may be carbon fiber reinforced plastic.

The manufacturing method for such a golf shaft 1 involves winding prepreg 21 around the outer surface 17a of the mandrel 17 while positioning the radial protrusions 19, and then hardening the prepreg 21 to form a hollow tube 3 having a thin-walled portion 11.

The protrusions 19 are preferably integral with the mandrel 17, but may be separate from the mandrel 17.

The protrusions 19 are preferably arranged circumferentially around the mandrel 17 in accordance with the thin-walled portion 11 of the tube body 3.

In addition, it is preferable that the protrusion 19 has an outer diameter larger than the basic shape 29 formed by the line segment connecting the outer diameter of the tip end 23 and the outer diameter of the base end 25 of the mandrel 17, depending on the thin-walled portion 11.

Depending on the thin-walled portion 11, the protrusion 19 is preferably positioned in a range of 150 mm to 688 mm from the tip 3a of the tube 3 when the length of the tube 3 is 838 mm, and in a range of 150 mm to 1044 mm from the tip 3a of the tube 3 when the length of the tube 3 is 1194 mm.

The protrusion 19 may have recesses 20 on both axial sides thereof, the recesses 20 having an outer diameter smaller than the basic shape 29 of the mandrel 17.

The prepreg 21 may be a carbon fiber sheet impregnated with resin, depending on the material of the golf shaft 1.

[Golf shaft structure]
Fig. 1 is a schematic longitudinal section of a golf shaft according to Example 1 of the present invention. Fig. 2 is a transverse section along line II-II in Fig. 1. Note that the longitudinal section refers to a section along the axial direction of the golf shaft, and the transverse section refers to a section perpendicular to the axial direction.

The golf shaft 1 in FIG. 1 is made of fiber-reinforced plastic, particularly carbon-reinforced plastic, and has a hollow tube 3. The material of the tube 3 is not particularly limited, and it can be made of other fiber-reinforced plastics, metal, or a composite material.

The cross-sectional shape of the tube 3 is circular. However, the cross-sectional shape of the tube 3 may be other shapes such as ellipse. The length of the tube 3 is 838 mm to 1194 mm. However, the golf shaft 1 can be set to be shorter than 838 mm or longer than 1194 mm, but is generally in the range of 838 mm to 1194 mm.

The tube body 3 is composed of a tip portion 5, a base portion 7, and an intermediate portion 9.

The tip portion 5 is the tip portion in the axial direction, and refers to a region within a specified range from the tip 3a of the tube body 3 in the axial direction. In this embodiment, the tip portion 5 is the portion to which the head of a golf club is attached. This tip portion 5 has a tapered outer surface in which the outer diameter gradually increases slightly toward the base end 3b. However, the tip portion 5 may also be formed in a straight shape with a constant outer diameter.

The base end 7 is the base end of the tube 3 in the axial direction, and refers to a region within a predetermined range from the base end 3b of the tube 3 in the axial direction. In this embodiment, the base end 7 is the portion to which the grip of a golf club is attached. This base end 7 has a straight outer surface with a constant outer diameter. However, the outer surface of the base end 7 may also be tapered, with the outer diameter gradually changing slightly toward the base end 3b.

The intermediate portion 9 is located between the tip portion 5 and the base portion 7, and has a tapered outer surface with a gradually increasing outer diameter toward the base portion 3b. Therefore, the tube body 3 has a tapered outer surface with a gradually increasing outer diameter between the tip portion 5 and the base portion 7.

The tube body 3 has a thin-walled portion 11 and a thick-walled portion 13.

The thin-walled portion 11 is a portion with a relatively small thickness. The thin-walled portion 11 is provided continuously in a circumferential manner with respect to the tube body 3. Note that it is also possible to provide multiple thin-walled portions 11 in a discontinuous circumferential manner. It is also possible to provide the thin-walled portions 11 in a non-circumferential manner, spaced apart on both sides in the radial direction.

This thin-walled portion 11 has an inner diameter larger than the corresponding portion of the basic shape 15. As a result, the thickness of the thin-walled portion 11 is thinner than the corresponding portion of the basic shape 15. The basic shape 15 is defined by a line segment (straight line) connecting the outer surface of the intermediate portion 9 with the inner diameter of the tip portion 5 and the inner diameter of the base portion 7.

The inner and outer diameters of the distal end 5 may be at any part of the distal end 5. The inner and outer diameters of the proximal end 7 may be at any part of the proximal end 7. Preferably, the inner and outer diameters of the distal end 5 and the proximal end 7 are at the boundary with the intermediate portion 9.

The thin-walled portion 11 in this embodiment has a tapered inner surface 11a in which the inner diameter gradually increases from both sides in the axial direction. As a result, the thickness of the thin-walled portion 11 gradually decreases from both sides in the axial direction. The thickness of the thin-walled portion 11 at its thinnest point is, for example, 1.03 mm to 1.46 mm, which is 98% to 99% of the thickness of the basic shape 15 at the same point (corresponding point) in the axial direction.

When the length of the tube 3 is 838 mm to 1194 mm, the position of the thin-walled portion 11 is in the range of 150 mm to 1044 mm from the tip 3a of the tube 3. More preferably, the position of the thin-walled portion 11 is in the range of 12% to 88% of the total length of the tube 3. When the length of the tube 3 is 838 mm, the position of the thin-walled portion 11 is preferably in the range of 150 mm to 688 mm from the tip 3a of the tube 3. When the length of the tube 3 is 1194 mm, the position of the thin-walled portion 11 is preferably in the range of 150 mm to 1044 mm from the tip 3a of the tube 3.

In this embodiment, the thinnest part of the thin-walled portion 11 is located in a range of 455 mm in length from the tip 3a (39% from the tip 3a of the tube 3), and the entire thin-walled portion 11 is located in a range of 392 mm to 597 mm in length from the tip (33% to 52% of the total length of the tube 3).

The thick-walled sections 13 are located on both sides of the thin-walled section 11 in the axial direction, and are relatively thick. Each thick-walled section 13 is provided continuously in a circumferential manner with respect to the tube body 3. However, it is also possible to provide multiple thick-walled sections 13 in a discontinuous circumferential manner. It is also possible to provide the thick-walled sections 13 in a non-circumferential manner, spaced apart on both sides in the radial direction.

This thick-walled portion 13 has an inner diameter smaller than the corresponding portion of the basic shape 15 of the tube body 3. As a result, the thickness of the thick-walled portion 13 is greater than the corresponding portion of the basic shape 15. However, the thick-walled portion 13 only needs to be at least thicker than the thin-walled portion 11, and may be as thick as the corresponding portion of the basic shape 15.

The thick-walled portion 13 in this embodiment has a tapered inner surface 13a in which the inner diameter gradually decreases from both sides in the axial direction. As a result, the thick-walled portion 13 gradually becomes thicker from both sides in the axial direction. The thickness of the thick-walled portion 13 at its thickest point is, for example, 1.06 mm to 1.56 mm, which is 101% to 105% of the thickness of the basic shape 15 at the same point (corresponding point) in the axial direction.

The thick-walled portion 13 may be located in a region adjacent to the thin-walled portion 11 in the axial direction. In this embodiment, the thickest part of the thick-walled portion 13 is located in a range of 330 mm (28% from the tip 3a of the tube 3) and 740 mm (64% from the tip 3a of the tube 3) from the tip, and the entire thick-walled portion 13 is located in a range of 155 mm to 392 mm (13% to 33% of the total length of the tube 3) and 597 mm to 900 mm (52% to 77% of the total length of the tube 3) from the tip.

The number of thick portions 13 and thin portions 11 can be set arbitrarily; for example, it is possible to provide two or more thin portions 11 and three or more thick portions 13.

[Function of Golf Shaft]
Figures 3(A) and (B) are schematic diagrams showing the bending and return of the golf shaft 1, with Figure 3(A) being an embodiment and Figure 3(B) being a comparative example. Figure 4 is a cross-sectional view showing the crushing of the thin-walled portion 11. The comparative example in Figure 3(B) is the same as the golf shaft 1 of Example 1, except that it does not have the thin-walled portion 11 and the thick-walled portion 13.

In the golf shaft 1 of this embodiment, the thin-walled portion 11 is easily crushed when the user swings. Crushing refers to the tube body 3 being crushed radially inward in the cross section of the golf shaft 1, and in this embodiment, this refers to the tube body 3 being deformed to be flattened so that the cross section of the tube body 3 becomes elliptical.

Specifically, in the golf shaft 1, flexion and rebound occur during a swing, as shown in Figure 3 (A). Bending is a gradual deformation toward the rear in the swing direction toward the tip 5, and rebound is a gradual deformation toward the front in the swing direction toward the tip 5, which is the opposite of bending.

As shown in Figures 1, 3(A) and 4, when the golf shaft 1 of this embodiment flexes, the thin-walled sections 11 bend first, collapsing and bending due to the presence of the thick-walled sections 13 on both sides. At this time, the thin-walled sections 11 are thinner than the corresponding parts of the basic shape 15 and therefore more easily collapsed, so they bend first while collapsing more reliably.

In addition, the golf shaft 1 has a gradual thickness from the thin section 11 to the thick section 13, which prevents sudden changes in thickness and avoids stress concentration, thereby preventing breakage.

The return to normal occurs when the thin-walled portion 11 first returns to a circular shape and then bends again while collapsing in the opposite direction. Even during this return to normal, the thin-walled portion 11 is prone to collapsing due to the presence of the thick-walled portions 13 on both sides and because it is thinner than the corresponding parts of the basic shape.

On the other hand, typical bending and rebound does not have any preceding bending, as shown in FIG. 3(B), and results in overall bending and rebound of the golf shaft 1. Compared to this case, in this embodiment, the absolute values of the amount of bending and rebound can be made smaller. Therefore, with the golf shaft 1 of this embodiment, bending and rebound can be reliably obtained and easily controlled.

In addition, in the golf shaft 1 of this embodiment, the absolute values of the amount of flex and the amount of return to flex are reduced, thereby preventing the dynamic loft D from becoming excessively large, and an appropriate dynamic loft D can be obtained. The dynamic loft D is the loft actually imparted to the ball at the time of impact.

Furthermore, in the golf shaft 1 of this embodiment, the attack angle A becomes gentler due to bending and returning, so the spin angle S can be suppressed. The attack angle A is the angle of incidence to the ball, and the spin angle S is the angle between the attack angle A and the dynamic loft D. As a result, the amount of spin can be reduced.

Figure 5 is a graph showing the degree of crushing of the golf shaft 1 of this embodiment, Figure 6(A) is a schematic diagram showing the method for measuring the degree of crushing, and Figure 6(B) is a graph showing the measurement results of the degree of crushing. The higher the degree of crushing, the easier it is to crush. The degree of crushing was calculated by performing three-point bending on the golf shaft 1 and based on the amount of deflection and bending rigidity at this time.

The bending stiffness is calculated by bending the golf shaft 1 over measurement span L as shown in Figure 6 (A) and measuring the load at this time. The measurement span L was set to 300 mm. When the amount of bending is changed, a difference in bending stiffness (bending stiffness difference) occurs compared to before the amount of bending was changed, as shown in Figure 6 (B). This is because crushing occurs as shown in Figure 4, and the greater the amount of bending, the greater the impact. This bending stiffness difference is defined as the degree of crushing.

As shown in Figure 5, in the golf shaft 1 of this embodiment, it can be seen that the degree of crushing is greater in the thin-walled portion 11 than on either side in the axial direction.

Figures 7(A) and (B) are graphs showing the results of test shots by different users. User A has a head speed of 43.5 m/s, and User B has a head speed of 39.9 m/s.

Figures 7(A) and (B) show error ellipses based on plots of the results of test shots of the golf shaft 1 of the embodiment and the golf shaft of the comparative example. The comparative example is identical to the golf shaft 1 of the embodiment 1, except that it does not have the thin portion 11 and the thick portion 13.

As shown in Figures 7(A) and (B), for all users, the error ellipse is closer to the ideal values of dynamic loft D and attack angle A when test hitting with the golf shaft 1 of the embodiment.

Figure 8 is a graph showing the ideal values for dynamic loft D and attack angle A. As shown in Figure 8, the ideal values are for optimizing the launch angle and spin rate to increase the flight distance, and differ for each head speed.

As shown in Figure 8, even though the ideal values differ for each head speed, the golf shaft 1 of the embodiment is able to bring the dynamic loft D and attack angle A closer to the ideal values for both users A and B, who have different head speeds.

In this way, the golf shaft 1 of this embodiment has a hollow tube 3 with a tapered outer surface in which the outer diameter gradually increases between the tip end 5 and the base end 7. Between the tip end 5 and the base end 7, the tube 3 has a thin-walled section 11 with a relatively small thickness due to the change in inner diameter, and thick-walled sections 13 located on both sides of this thin-walled section 11 in the axial direction and with a relatively large thickness.

As a result, in the golf shaft 1, bending and straightening occur in the thin-walled portion 11 before the tube body 3, allowing any user to obtain an appropriate bending motion. In addition, in the golf shaft 1, the absolute value of the amount of bending and straightening can be made small, making it easy to control while still obtaining bending and straightening motion reliably.

The thin-walled portion 11 is arranged in a circular pattern, allowing for smooth crushing.

The thin-walled portion 11 has an inner diameter larger than the corresponding portion of the basic shape 15, which is made up of the line segments connecting the inner and outer diameters of the tip end 5 and the base end 7. Therefore, the thin-walled portion 11 of the golf shaft 1 can be crushed reliably, and appropriate flex can be obtained regardless of the user.

In addition, when the length of the tube 3 is 838 mm to 1194 mm, the thin-walled portion 11 is located in a range of 150 mm to 1044 mm from the tip 3a of the tube 3, so that appropriate flexibility can be obtained regardless of the user.

[Manufacturing method of golf shafts]
9(A) to (C) are vertical cross-sectional views showing a manufacturing method of golf shaft 1, in which FIG. 9(A) shows a mandrel, FIG. 9(B) shows the state in which prepreg has been wound around the mandrel of FIG. 9(A), and FIG. 9(C) shows the state in which tape has been wound around the prepreg of FIG. 9(B).

In the manufacturing method of the golf shaft 1 of this embodiment, the prepreg 21 is wound around the outer surface 17a of the mandrel 17 while the radial protrusions 19 are positioned on the outer surface 17a as shown in Figures 9(A) and (B).

The mandrel 17 is rod-shaped, and the outer diameter of the surface gradually increases from the tip to the base end. The mandrel 17 of this embodiment corresponds to the golf shaft 1 and has a tip portion 23, an intermediate portion 25, and a base end portion 27. The tip portion 23 has an outer surface with a constant outer diameter from the tip 17b. The intermediate portion 25 has a protrusion 19 and a recess 20. The base end portion 27 has an outer surface with an outer diameter that gradually increases toward the base end 17c.

In this embodiment, the protrusion 19 is integral with the mandrel 17, but it may be formed separately. The shape of the protrusion 19 is such that it fits into the thin-walled portion 11. Therefore, the protrusion 19 in this embodiment is provided in a circumferential shape, and the outer diameter gradually increases from both sides in the axial direction. This protrusion 19 has an outer diameter larger than the corresponding portion of the basic shape 29 of the mandrel 17. The basic shape 29 is made up of a line segment (straight line) connecting the outer diameter of the tip portion 23 and the outer diameter of the base portion 27. In addition, the protrusion 19 is located in a position corresponding to a portion of the tube 3 whose length from the tip 3a is in the range of 150 mm to 1044 mm when the length of the tube 3 is 838 mm to 1194 mm.

When the length of the tube 3 is 838 mm, the protrusion 19 is located in a position corresponding to the portion of the tube 3 whose length from the tip 3a is in the range of 150 mm to 688 mm. When the length of the tube 3 is 1194 mm, the protrusion 19 is located in a position corresponding to the portion of the tube 3 whose length from the tip 3a is in the range of 150 mm to 1044 mm.

The recesses 20 are located on both axial sides of the protrusion 19, and are continuous with the protrusion 19 by an outer surface whose outer diameter gradually decreases from the protrusion 19 in correspondence with the thick-walled portion 13. The recesses 20 have an outer diameter smaller than the corresponding portion of the basic shape 29 formed by the line segment connecting the outer diameter of the tip end 23 and the outer diameter of the base end 27 of the mandrel 17.

Multiple sheets of prepreg 21 having a predetermined cut shape and dimensions are wound around mandrel 17. This winding is performed so that prepreg 21 follows the outer surface of mandrel 17 having protrusions 19. Figure 10 shows a development of prepreg 21. In the example of Figure 10, six prepregs 21 are used. The number of prepregs 21 is appropriately set according to the characteristics of golf shaft 1.

Each prepreg 21 is a fiber sheet impregnated with resin. The resin is not particularly limited, but may be epoxy resin, unsaturated polyester resin, phenol resin, etc. The fiber sheet may be, for example, a sheet of inorganic fibers such as metal fiber, boron fiber, carbon fiber, glass fiber, ceramic fiber, aramid fiber, or other high-strength synthetic fibers. Inorganic fibers are preferably used because they are lightweight and strong. Among them, carbon fiber is most suitable because it has excellent specific strength and specific rigidity. Therefore, in this embodiment, a carbon fiber sheet is used as the fiber sheet.

After wrapping the prepreg 21 around the mandrel 17, as shown in FIG. 9(C), tape 31 is further wrapped around it to keep the prepreg 21 wrapped around the mandrel 17. Heating is then performed in this state to harden the prepreg 21, resulting in a tubular semi-finished product. After removing the tape 31, the outer surface of the semi-finished product is polished to become the tubular body 3 of the golf shaft 1 shown in FIG. 1.

As described above, the tube body 3 has a relatively thin walled portion 11 between the tip end 5 and the base end 7 at the portion corresponding to the protrusion 19, and has relatively thick walled portions 13 on both sides of the thin walled portion 11 in the axial direction.

As a result, it is possible to realize a golf shaft 1 that can provide appropriate flex regardless of the user.

1 Golf shaft 3 Tube 5 Tip (Tube)
7 Base end (tube body)
9. Middle section (tube body)
11 Thin-walled portion 13 Thick-walled portion 15 Basic shape (tube body)
17 Mandrel 19 Protrusion 21 Prepreg 23 Tip (mandrel)
25 Middle section (mandrel)
27 Base end (mandrel)
29 Basic shape (mandrel)

Claims (13)

The catheter has a hollow tube having a tapered outer surface whose outer diameter gradually increases between a distal end and a proximal end,
Between the tip end and the base end, the tube includes a thin-walled portion having a relatively small wall thickness due to a change in inner diameter, and thick-walled portions located on both sides of the thin-walled portion in the axial direction and having a relatively large wall thickness.
Golf shaft. 2. The golf shaft of claim 1,
The thin portion is provided in a circumferential shape.
Golf shaft. 3. The golf shaft of claim 2,
The thin-walled portion has an inner diameter larger than a corresponding portion of the basic shape including a line segment connecting the inner diameter of the tip portion and the inner diameter of the base end portion.
Golf shaft. 4. The golf shaft of claim 3,
The length of the tube is between 838 mm and 1194 mm;
When the length of the tube is 838 mm, the thin-walled portion is located in a range of 150 mm to 688 mm from the tip of the tube, and when the length of the tube is 1194 mm, the thin-walled portion is located in a range of 150 mm to 1044 mm from the tip of the tube.
Golf shaft. 3. The golf shaft of claim 2,
The thick-walled portion has an inner diameter smaller than a corresponding portion of a basic shape including a line segment connecting an inner diameter of the tip portion and an inner diameter of the base portion.
Golf shaft. A golf shaft according to any one of claims 1 to 5,
The tube body is made of carbon fiber reinforced plastic.
Golf shaft. The prepreg is wound around the surface of the mandrel while positioning the radial projections on the surface of the mandrel.
The prepreg is cured to form a hollow tube.
the tube has a thin-walled portion having a relatively small thickness between the distal end and the proximal end, the thin-walled portion being located at a portion corresponding to the protrusion, and has thick-walled portions having a relatively large thickness on both sides of the thin-walled portion in the axial direction;
A method for manufacturing a golf shaft. 8. A method for manufacturing a golf shaft according to claim 7, comprising the steps of:
The protrusion is integrally formed on the mandrel.
A method for manufacturing a golf shaft. 8. A method for manufacturing a golf shaft according to claim 7, comprising the steps of:
The protrusion is provided circumferentially around the mandrel.
A method for manufacturing a golf shaft. 8. A method for manufacturing a golf shaft according to claim 7, comprising the steps of:
The projection has an outer diameter larger than a corresponding portion of a basic shape including a line segment connecting the outer diameter of the tip end portion and the outer diameter of the base end portion of the mandrel.
A method for manufacturing a golf shaft. 8. A method for manufacturing a golf shaft according to claim 7, comprising the steps of:
The length of the tube is between 838 mm and 1194 mm;
When the length of the tube is 838 mm, the protrusion is positioned in a range of 150 mm to 688 mm from the tip of the tube, and when the length of the tube is 1194 mm, the protrusion is positioned in a range of 150 mm to 1044 mm from the tip of the tube.
A method for manufacturing a golf shaft. 8. A method for manufacturing a golf shaft according to claim 7, comprising the steps of:
a recess having an outer diameter smaller than a corresponding portion of a basic shape including a line segment connecting an outer diameter of the tip end portion and an outer diameter of the base end portion of the mandrel, on both sides of the projection in the axial direction;
A method for manufacturing a golf shaft. A method for manufacturing a golf shaft according to any one of claims 7 to 12, comprising the steps of:
The prepreg is a carbon fiber sheet impregnated with resin.
A method for manufacturing a golf shaft.