Golf shaft and method for manufacturing same

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

[0001] The present invention relates to a golf shaft and a method for manufacturing the same.

[0002] It is known that a golf club can improve the flight distance and stability of a ball by utilizing the flexibility of its shaft (hereinafter referred to as a golf shaft) during a swing.

[0003] 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 position of the kick point.

[0004] However, the golf shaft of Patent Document 1 is designed to provide an appropriate flex when the user is above a certain level, so it may be difficult for some users to obtain the appropriate flex.

[0005] JP 2023-63540 A

[0006] The problem it aims to solve is the difficulty some users have in obtaining the appropriate flex.

[0007] The present invention provides a golf shaft having a hollow tubular body with a tapered outer surface in which the outer diameter gradually increases between the tip end and the base end, wherein the tubular body has a thin-walled portion with a relatively small thickness due to the change in inner diameter between the tip end and the base end, and thick-walled portions with a relatively large thickness located on both sides of the thin-walled portion in the axial direction.

[0008] 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 tubular body, the tubular body having a relatively thin-walled portion between the tip end and the base end corresponding to the protrusions, and a relatively thick-walled portion on either side of the thin-walled portion in the axial direction.

[0009] The present invention makes it possible to realize a golf shaft that can provide an appropriate flex for any user.

[0010] FIG. 1 is a schematic longitudinal sectional view of a golf shaft according to an embodiment of the present invention. FIG. 2 is a transverse sectional view taken along line II-II in FIG. 1. FIGS. 3(A) and (B) are schematic diagrams showing the flex and rebound of a golf shaft, with FIG. 3(A) being an embodiment and FIG. 3(B) being a comparative example. FIG. 4 is a transverse sectional view showing the crushing of the thin-walled portion of the golf shaft of FIG. 1. FIG. 5 is a graph showing the degree of crushing of the thin-walled portion of the golf shaft of FIG. 1. FIG. 6(A) is a schematic diagram showing a method for measuring the degree of crushing, and FIG. 6(B) is a graph showing the measurement results of the degree of crushing. FIGS. 7(A) and (B) are graphs showing the results of test shots by different users. FIG. 8 is a graph showing ideal values ​​for dynamic angle and attack angle. Figures 9(A) to 9(C) are longitudinal cross-sectional views showing a manufacturing method of golf shaft 1, with Figure 9(A) showing a mandrel, Figure 9(B) showing a state in which prepreg has been wrapped around the mandrel of Figure 9(A), and Figure 9(C) showing a state in which tape has been wrapped around the prepreg of Figure 9(B). Figure 10 is a development view showing an example of the prepreg of Figure 9.

[0011] The objective of realizing a golf shaft that can provide appropriate flexibility regardless of the user has been achieved by providing a thin-walled portion in the middle of the golf shaft.

[0012] The golf shaft 1 includes a hollow tubular body 3 having a tapered outer surface with an outer diameter that gradually increases between the tip end 5 and the base end 7. Between the tip end 5 and the base end 7, the tubular body 3 includes a thin-walled portion 11 and a thick-walled portion 13 due to the change in inner diameter. The thin-walled portion 11 has a relatively small thickness. The thick-walled portions 13 are located on both sides of the thin-walled portion 11 in the axial direction and have a relatively large thickness.

[0013] The thin-walled portion 11 may be provided in a circumferential direction or may be provided partially in the circumferential direction.

[0014] The thin-walled portion 11 preferably has an inner diameter larger than the basic shape 15 including the line segment connecting the inner diameter of the distal end portion 5 and the inner diameter of the proximal end portion 7 .

[0015] The length of the tube 3 can be set within a range of, for example, 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 3 is 838 mm, the thin-walled portion 11 is located within a range of 150 mm to 688 mm from the tip 3 a of the tube 3, and when the length of the tube 3 is 1194 mm, the thin-walled portion 11 is located within a range of 150 mm to 1044 mm from the tip 3 a of the tube 3.

[0016] The thickened portion 13 may have an inner diameter smaller than the basic shape 15 .

[0017] The material of the tube body 3 of the golf shaft 1 can be any appropriate material, but may be carbon fiber reinforced plastic.

[0018] The manufacturing method of such a golf shaft 1 involves winding prepreg 21 around the outer surface 17a of a mandrel 17 while positioning the radial protrusions 19 on the outer surface 17a, and then curing the prepreg 21 to form a hollow tubular body 3 having a thin-walled portion 11.

[0019] The projections 19 are preferably provided integrally with the mandrel 17, but may also be separate from the mandrel 17.

[0020] The projections 19 are preferably provided around the mandrel 17 in accordance with the thin-walled portion 11 of the tube 3 .

[0021] Furthermore, it is preferable that the projection 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 according to the thin-walled portion 11 .

[0022] 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.

[0023] The projection 19 may have recesses 20 on both sides in the axial direction, each recess 20 having an outer diameter smaller than the basic shape 29 of the mandrel 17 .

[0024] The prepreg 21 may be a carbon fiber sheet impregnated with resin depending on the material of the golf shaft 1 .

[0025] [Golf Shaft Structure] Fig. 1 is a schematic longitudinal cross-sectional view of a golf shaft according to Example 1 of the present invention. Fig. 2 is a transverse cross-sectional view taken along line II-II in Fig. 1. Note that the longitudinal cross-section refers to a cross-section along the axial direction of the golf shaft, and the transverse cross-section refers to a cross-section perpendicular to the axial direction.

[0026] 1 is a shaft made of fiber-reinforced plastic, particularly carbon-reinforced plastic, and includes 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.

[0027] 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.

[0028] The tubular body 3 is composed of a distal end portion 5 , a proximal end portion 7 , and an intermediate portion 9 .

[0029] The distal end 5 is the distal end in the axial direction and refers to a region extending in a predetermined range from the distal end 3a of the tube 3 in the axial direction. In this embodiment, the distal end 5 is the portion to which the head of a golf club is attached. The distal end 5 has a tapered outer surface in which the outer diameter gradually increases slightly toward the base end 3b. However, the distal end 5 may also be formed straight with a constant outer diameter.

[0030] The base end 7 is the base end of the tubular body 3 in the axial direction, and refers to a predetermined area from the base end 3b of the tubular body 3 in the axial direction. In this embodiment, the base end 7 is the portion to which a golf club grip is attached. The base end 7 has a straight outer surface with a constant outer diameter. However, the outer surface of the base end 7 may be tapered so that the outer diameter gradually changes slightly toward the base end 3b.

[0031] The intermediate portion 9 is located between the distal end portion 5 and the proximal end portion 7, and has a tapered outer surface whose outer diameter gradually increases slightly toward the proximal end 3b. Therefore, the tubular body 3 has a tapered outer surface whose outer diameter gradually increases between the distal end portion 5 and the proximal end portion 7.

[0032] The pipe body 3 has a thin-walled portion 11 and a thick-walled portion 13 .

[0033] The thin-walled portion 11 is a portion having a relatively small thickness. The thin-walled portion 11 is provided continuously around the tubular body 3. It is also possible to provide a plurality of thin-walled portions 11 in a discontinuous manner around the tubular body 3. It is also possible to provide the thin-walled portions 11 in a non-circular manner, spaced apart from each other on both sides in the radial direction.

[0034] This thin-walled portion 11 has an inner diameter larger than that of the corresponding portion of the basic shape 15. As a result, the thickness of the thin-walled portion 11 is thinner than that of 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 end portion 5 and the inner diameter of the base end portion 7.

[0035] The inner diameter and outer diameter of the distal end portion 5 may be at any part of the distal end portion 5. The inner diameter and outer diameter of the proximal end portion 7 may also be at any part of the proximal end portion 7. Preferably, the inner diameter and outer diameter of the distal end portion 5 and the proximal end portion 7 are at the boundary portion with the intermediate portion 9.

[0036] The thin-walled portion 11 of 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.

[0037] 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.

[0038] 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 body 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 body 3).

[0039] The thick-walled portions 13 are located on both sides of the thin-walled portion 11 in the axial direction and are portions with a relatively large thickness. Each thick-walled portion 13 is provided continuously around the tube body 3. However, it is also possible to provide a plurality of thick-walled portions 13 in a discontinuous manner around the tube body 3. It is also possible to provide the thick-walled portions 13 in a non-circular manner, spaced apart on both sides in the radial direction.

[0040] The thick-walled portion 13 has an inner diameter smaller than that of the corresponding portion of the basic shape 15 of the tube 3. As a result, the thickness of the thick-walled portion 13 is greater than that of the corresponding portion of the basic shape 15. However, the thick-walled portion 13 only needs to be thicker than the thin-walled portion 11, and may have the same thickness as that of the corresponding portion of the basic shape 15.

[0041] The thick-walled portion 13 of 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 thickness of the thick-walled portion 13 gradually increases 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.

[0042] 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) in length 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) in length from the tip.

[0043] The number of thick portions 13 and thin portions 11 can be set arbitrarily, and for example, two or more thin portions 11 and three or more thick portions 13 can be provided.

[0044] [Function of Golf Shaft] Figures 3(A) and (B) are schematic diagrams showing the flexing and recovery of the golf shaft 1, with Figure 3(A) being an example 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 identical to the golf shaft 1 of Example 1 except that it does not have the thin-walled portion 11 or the thick-walled portion 13.

[0045] 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 so that its cross section becomes flattened into an elliptical shape.

[0046] Specifically, the golf shaft 1 undergoes bending and straightening during a swing, as shown in Figure 3(A). Bending is a gradual deformation toward the rear in the swing direction toward the tip portion 5, and straightening is a gradual deformation toward the front in the swing direction toward the tip portion 5, which is the opposite of bending.

[0047] 1, 3(A), and 4, when the golf shaft 1 of this embodiment flexes, the thin-walled portions 11 bend first, collapsing due to the presence of the thick-walled portions 13 on both sides. At this time, the thin-walled portions 11 are thinner than the corresponding portions of the basic shape 15 and therefore more easily collapse, so they bend first while collapsing more reliably.

[0048] Furthermore, in the golf shaft 1, the thickness gradually increases from the thin portion 11 to the thick portion 13, which prevents abrupt changes in thickness and prevents stress concentration, thereby suppressing breakage.

[0049] The thin-walled portion 11 returns to its circular shape and then bends again while collapsing in the opposite direction. Even during this return, the thin-walled portion 11 is easily collapsed due to the presence of the thick-walled portions 13 on both sides and the fact that it is thinner than the corresponding portions of the basic shape.

[0050] On the other hand, typical flex and rebound are not preceded by a preceding flex, but rather are the overall flex and rebound of the golf shaft 1, as shown in Figure 3(B). Compared to this case, in this embodiment, the absolute values ​​of the flex and rebound amounts can be made smaller. Therefore, with the golf shaft 1 of this embodiment, flex and rebound are reliably obtained and are easy to control.

[0051] Furthermore, in the golf shaft 1 of this embodiment, by reducing the absolute values ​​of the amount of flex and the amount of return to flex, it is possible to prevent the dynamic loft D from becoming excessively large and obtain an appropriate dynamic loft D. The dynamic loft D is the loft actually imparted to the ball at the time of impact.

[0052] Furthermore, in the golf shaft 1 of this embodiment, the attack angle A becomes gentler due to bending and returning, thereby suppressing the spin angle S. The attack angle A is the angle of incidence with respect to the ball, and the spin angle S is the angle formed by the attack angle A and the dynamic loft D. As a result, the amount of spin can be reduced.

[0053] Fig. 5 is a graph showing the degree of collapse of the golf shaft 1 of this example, Fig. 6(A) is a schematic diagram showing a method for measuring the degree of collapse, and Fig. 6(B) is a graph showing the measurement results of the degree of collapse. The higher the degree of collapse, the easier it is to collapse. The degree of collapse was calculated based on the amount of deflection and bending rigidity of the golf shaft 1 when three-point bending was performed.

[0054] Here, the bending stiffness is calculated by bending the golf shaft 1 over a 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 crushing degree.

[0055] As shown in FIG. 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 both sides in the axial direction.

[0056] 7A and 7B are graphs showing the results of test shots by different users. User A had a head speed of 43.5 m / s, and User B had a head speed of 39.9 m / s.

[0057] 7A and 7B show error ellipses based on plots of the results of test hits with the golf shaft 1 of the example and the golf shaft of the comparative example. The comparative example is identical to the golf shaft 1 of the example 1 except that it does not have the thin-walled portion 11 and the thick-walled portion 13.

[0058] As shown in FIGS. 7A and 7B, for all users, the error ellipse is closer to the ideal values ​​of the dynamic loft D and the attack angle A when the golf shaft 1 of the embodiment is used for the test hit.

[0059] Figure 8 is a graph showing ideal values ​​for dynamic loft D and attack angle A. As shown in Figure 8, the ideal values ​​are used to optimize the launch angle and spin rate to increase distance, and vary depending on the head speed.

[0060] As shown in Figure 8, although the ideal values ​​differ depending on the 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.

[0061] As described above, the golf shaft 1 of this embodiment comprises a hollow tubular body 3 having 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 tubular body 3 comprises a thin-walled portion 11 having a relatively small thickness due to the change in inner diameter, and thick-walled portions 13 located on both sides of the thin-walled portion 11 in the axial direction and having a relatively large thickness.

[0062] For this reason, in the golf shaft 1, flexion and recovery occur in the thin-walled portion 11 before the tubular body 3, allowing any user to obtain an appropriate flex. Also, in the golf shaft 1, the absolute values ​​of the flex and recovery amounts can be made small, making it easy to control the flex and recovery while reliably obtaining it.

[0063] The thin-walled portion 11 is provided in a circumferential shape, so that it can be crushed smoothly.

[0064] The thin-walled portion 11 has an inner diameter larger than the corresponding portion of the basic shape 15 formed by the line segments connecting the inner and outer diameters of the tip end portion 5 and the base end portion 7. Therefore, the thin-walled portion 11 of the golf shaft 1 can be reliably crushed, and an appropriate flex can be obtained regardless of the user.

[0065] Furthermore, when the length of the tube body 3 is 838 mm to 1194 mm, the thin-walled portion 11 is located in a length range from 150 mm to 1044 mm from the tip 3a of the tube body 3, so that a more appropriate flex can be obtained regardless of the user.

[0066] [Manufacturing Method of Golf Shaft] Figures 9(A) to (C) are longitudinal cross-sectional views showing a manufacturing method of golf shaft 1, with Figure 9(A) showing a mandrel, Figure 9(B) showing the state where prepreg has been wrapped around the mandrel of Figure 9(A), and Figure 9(C) showing the state where tape has been wrapped around the prepreg of Figure 9(B).

[0067] 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 projections 19 are positioned on the outer surface 17a, as shown in FIGS. 9(A) and 9(B).

[0068] 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.

[0069] In this embodiment, the protrusion 19 is integral with the mandrel 17, but may be formed separately. The protrusion 19 has a shape that fits into the thin-walled portion 11. Therefore, the protrusion 19 in this embodiment is provided circumferentially, and the outer diameter gradually increases from both sides in the axial direction. This protrusion 19 has an outer diameter larger than that of a corresponding portion of the basic shape 29 of the mandrel 17. The basic shape 29 is formed by a line segment (straight line) connecting the outer diameter of the distal end portion 23 and the outer diameter of the proximal end portion 27. Furthermore, when the length of the tube 3 is 838 mm to 1194 mm, the protrusion 19 is located in a portion of the tube 3 that is 150 mm to 1044 mm from the distal end 3a.

[0070] When the length of the tube 3 is 838 mm, the protrusion 19 is located in a 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 portion of the tube 3 whose length from the tip 3a is in the range of 150 mm to 1044 mm.

[0071] The recesses 20 are located on both axial sides of the projection 19 and are continuous with the projection 19 by an outer surface whose outer diameter gradually decreases in correspondence with the thick-walled portion 13. The recesses 20 have an outer diameter smaller than that of 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.

[0072] A plurality of prepreg sheets 21 having a predetermined cut shape and dimensions are wound around the mandrel 17. This winding is performed so that the prepreg sheets 21 fit along the outer surface of the mandrel 17 having the projections 19. FIG. 10 shows a development of the prepreg sheets 21. In the example of FIG. 10, six prepreg sheets 21 are used. The number of prepreg sheets 21 is set appropriately depending on the characteristics of the golf shaft 1.

[0073] Each prepreg 21 is a fiber sheet impregnated with resin. The resin is not particularly limited, but may be epoxy resin, unsaturated polyester resin, phenolic resin, or the like. The fiber sheet may be made of inorganic fibers such as metal fiber, boron fiber, carbon fiber, glass fiber, or ceramic fiber, or aramid fiber or other high-strength synthetic fibers. Inorganic fibers are preferably used because they are lightweight and strong. Of these, 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.

[0074] After the prepreg 21 is wound around the mandrel 17, as shown in Figure 9(C), tape 31 is further wound around the mandrel 17 to maintain the prepreg 21 wound around the mandrel 17. Heating in this state hardens 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 form the tubular body 3 of the golf shaft 1 shown in Figure 1.

[0075] As described above, the tube body 3 has a thin-walled portion 11 with a relatively small thickness between the tip end 5 and the base end 7 in the portion corresponding to the protrusion 19, and has thick-walled portions 13 with a relatively large thickness on both sides of this thin-walled portion 11 in the axial direction.

[0076] Therefore, it is possible to realize a golf shaft 1 that can provide an appropriate flex regardless of the user.

[0077] REFERENCE SIGNS LIST 1 Golf shaft 3 Tube 5 Tip portion (tube) 7 Base portion (tube) 9 Intermediate portion (tube) 11 Thin portion 13 Thick portion 15 Basic shape (tube) 17 Mandrel 19 Protrusion 21 Prepreg 23 Tip portion (mandrel) 25 Intermediate portion (mandrel) 27 Base portion (mandrel) 29 Basic shape (mandrel)

Claims

1. A golf shaft comprising a hollow tubular body having a tapered outer surface whose outer diameter gradually increases between a tip end portion and a base end portion, wherein the tubular body 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 axial sides of the thin-walled portion and having a relatively large wall thickness between the tip end portion and the base end portion.

2. The golf shaft according to claim 1, wherein the thin-walled portion is provided in a circumferential shape.

3. The golf shaft according to claim 2, wherein the thin-walled portion has an inner diameter larger than a corresponding portion of a basic shape including a line segment connecting the inner diameter of the tip end portion and the inner diameter of the base end portion.

4. The golf shaft according to claim 3, wherein the length of the tubular body is 838 mm to 1194 mm, and the thin-walled portion is located in a range of 150 mm to 688 mm from the tip end of the tubular body when the length of the tubular body is 838 mm, and is located in a range of 150 mm to 1044 mm from the tip end of the tubular body when the length of the tubular body is 1194 mm.

5. The golf shaft according to claim 2, wherein the thick-walled portion has an inner diameter smaller than a corresponding portion of a basic shape including a line segment connecting the inner diameter of the tip end portion and the inner diameter of the base end portion.

6. The golf shaft according to any one of claims 1 to 5, wherein the tubular body is made of carbon fiber reinforced plastic.

7. A method for manufacturing a golf shaft, comprising winding a prepreg around a mandrel while positioning radial protrusions on the surface of the mandrel, and curing the prepreg to form a hollow tubular body, wherein the tubular body includes a thin-walled portion having a relatively small wall thickness at a portion corresponding to the protrusions and thick-walled portions having a relatively large wall thickness on both axial sides of the thin-walled portion between a tip end portion and a base end portion.

8. The method for manufacturing a golf shaft according to claim 7, wherein the protrusions are integrally provided on the mandrel.

9. The method for manufacturing a golf shaft according to claim 7, wherein the protrusions are provided in a circumferential shape with respect to the mandrel.

10. A method for manufacturing a golf shaft according to claim 7, wherein the protrusion has an outer diameter larger than that of 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.

11. A method for manufacturing a golf shaft according to claim 7, wherein the length of the tube body is 838 mm to 1194 mm, and the protrusion is positioned in a range of 150 mm to 688 mm from the tip end of the tube body when the length of the tube body is 838 mm, and when the length of the tube body is 1194 mm, the protrusion is positioned in a range of 150 mm to 1044 mm from the tip end of the tube body. A method for manufacturing a golf shaft.

12. A method for manufacturing a golf shaft according to claim 7, wherein recesses having an outer diameter smaller than that of 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 are provided on both sides in the axial direction of the protrusion. A method for manufacturing a golf shaft.

13. A method for manufacturing a golf shaft according to any one of claims 7 to 12, wherein the prepreg is a carbon fiber sheet impregnated with resin. A method for manufacturing a golf shaft.

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