U.S. patent application number 17/414016 was filed with the patent office on 2022-02-17 for golf club shaft and golf club.
The applicant listed for this patent is FUJIKURA COMPOSITES Inc.(formerly know as FUJIKURA RUBBER LTD.). Invention is credited to Yoshihito Kogawa, Keigo Takahashi.
Application Number | 20220047927 17/414016 |
Document ID | / |
Family ID | |
Filed Date | 2022-02-17 |
United States Patent
Application |
20220047927 |
Kind Code |
A1 |
Takahashi; Keigo ; et
al. |
February 17, 2022 |
GOLF CLUB SHAFT AND GOLF CLUB
Abstract
Provided are the golf club shaft and the golf club for offering
excellent feel of swing motions without demanding fine setting
while keeping advantages of the short-sized golf club shaft. The
golf club shaft includes a shaft body which extends in a
longitudinal direction, and a gravity center shifting member
attached to the shaft body for shifting a shaft gravity center
toward a distal-end side in the longitudinal direction. In the case
where the shaft body is cut to have a shaft full length of 43
inches or shorter, and positions of a distal-end portion and a
proximal-end portion in the longitudinal direction are defined by
percentage as 0% and 100%, respectively, a position of the shaft
gravity center is set to be in a range from 39% to 45%.
Inventors: |
Takahashi; Keigo;
(Saitama-shi, Saitama, JP) ; Kogawa; Yoshihito;
(Saitama-shi, Saitama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIKURA COMPOSITES Inc.(formerly know as FUJIKURA RUBBER
LTD.) |
Koto-ku,Tokyo |
|
JP |
|
|
Appl. No.: |
17/414016 |
Filed: |
December 17, 2018 |
PCT Filed: |
December 17, 2018 |
PCT NO: |
PCT/JP2018/046287 |
371 Date: |
June 15, 2021 |
International
Class: |
A63B 53/06 20060101
A63B053/06; A63B 53/10 20060101 A63B053/10 |
Claims
1. A golf club shaft, comprising: a shaft body which extends in a
longitudinal direction; and a gravity center shifting member which
is attached to the shaft body for shifting a shaft gravity center
toward a distal-end side in the longitudinal direction, wherein in
the case of cutting the shaft body to have a shaft full length of
43 inches or shorter, and defining positions of a distal-end
portion and a proximal-end portion in the longitudinal direction by
percentage as 0% and 100%, respectively, a position of the shaft
gravity center is set to be in a range from 39% to 45%.
2. The golf club shaft according to claim 1, wherein a cut length
of the shaft body at the proximal-end side in the longitudinal
direction is longer than a cut length of the shaft body at the
distal-end side in the longitudinal direction.
3. The golf club shaft according to claim 1, wherein a weight ratio
of the gravity center shifting member to the shaft body is set to
be in a range from 14% to 33%.
4. The golf club shaft according to claim 1, wherein the gravity
center shifting member includes a metal cylinder buried in an inner
circumferential surface of the shaft body.
5. The golf club shaft according to claim 1, wherein the shaft body
includes a first region having a shaft outer diameter relatively
gently reduced, a second region having the shaft outer diameter
relatively steeply reduced, and a third region having the smallest
relative change amount of the shaft outer diameter, which are
sequentially arranged from the proximal-end side toward the
distal-end side in the longitudinal direction.
6. The golf club shaft according to claim 5, wherein an occupancy
percentage of the first region in the longitudinal direction is 30%
or higher, an occupancy percentage of the second region in the
longitudinal direction is in a range from 45% to 60%, and an
occupancy percentage of the third region in the longitudinal
direction is in a range from 10% to 25%.
7. The golf club shaft according to claim 5, wherein a grip is
attached to an outer circumferential surface of the first region,
and a metal cylinder as the gravity center shifting member is
buried in an inner circumferential surface of the third region.
8. A golf club configured to have a club head and a grip attached
to the golf club shaft according to claim 1.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a National Stage application of
International Patent Application No. PCT/JP2018/046287 filed on
Dec. 17, 2018, which is hereby incorporated by reference in its
entirety.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention relates to a golf club shaft and a
golf club.
BACKGROUND OF THE INVENTION
[0003] The patent right has been granted to the applicant of the
present invention which relates to a golf club shaft (Japanese
Patent No. 4880063). Specifically, the golf club shaft includes a
metal cylinder entirely made of metal material, and a hollow
cylindrical shaft body which includes at least a part of the metal
cylinder in the longitudinal direction, and is produced through
thermosetting treatment of multiple unset thermosetting resin
prepregs which have been laminated and wound on the outer
circumference of the metal cylinder. The metal cylinder is located
at a part of the hollow cylindrical shaft body in the longitudinal
direction. At least an outer radial part of the metal cylinder is
buried in the burying recess cylindrical portion formed in the
inner wall of the shaft body to bring the hand-side cylindrical end
surface of the metal cylinder into abutment on the hand-side recess
cylindrical end surface of the burying recess cylindrical portion
of the shaft body.
SUMMARY OF THE INVENTION
[0004] The applicant, for example, has been proceeding with
research and development of the so-called short-sized golf club
shaft formed by cutting the shaft body with full length longer than
43 inches (for example, 45 inches or longer) to have its full
length of 43 inches or shorter. The short-sized golf club shaft can
be easily handled to accurately meet an impact at the sweet spot,
resulting in the improved meeting rate.
[0005] Meanwhile, the use of the short-sized golf club shaft is
likely to make especially the advanced golf player feel like
unnatural sense of swing motions, resulting in disadvantages that
the ball hitting angle tends to be small (difficulty in rise-up of
the ball). Increase in the club head weight to be heavier than the
club head to be attached to the normal-sized golf club shaft has
been taken into account for the purpose of using the short-sized
golf club shaft.
[0006] As increase in the club head weight affects the weight and
balance of the entire golf club, fine setting including adjustment
of the full length of the short-sized golf club shaft may be
demanded depending on the circumstances.
[0007] The present invention has been made in view of the
above-described problem, and it is an object of the present
invention to provide the golf club shaft and the golf club, which
are effective for offering excellent feel of swing motions without
demanding the fine setting while keeping advantages of the
short-sized golf club shaft.
[0008] The golf club shaft of the embodiment includes a shaft body
which extends in a longitudinal direction, and a gravity center
shifting member which is attached to the shaft body for shifting a
shaft gravity center toward a distal-end side in the longitudinal
direction. In the case where the shaft body is cut to have a shaft
full length of 43 inches or shorter, and positions of a distal-end
portion and a proximal-end portion in the longitudinal direction
are defined by percentage as 0% and 100%, respectively, a position
of the shaft gravity center is set to be in a range from 39% to
45%.
[0009] Assuming that each position of the distal-end portion and
the proximal-end portion in the longitudinal direction is defined
by percentage as 0% and 100%, respectively, it is preferable to set
the position of the shaft gravity center to be in the range from
41% to 44%, and more preferably, from 42.5% to 43.5%.
[0010] A cut length of the shaft body at the proximal-end side in
the longitudinal direction may be made longer than a cut length of
the shaft body at the distal-end side in the longitudinal
direction. The concept of the cut length applies to the case in
which the cut length at the distal-end side is zero. That is, there
may be the case of cutting the shaft body only at the proximal-end
side without cutting at the distal-end side besides the case of
cutting the shaft body both at the distal-end side and the
proximal-end side.
[0011] The weight ratio of the gravity center shifting member to
the shaft body may be set to be in a range from 14% to 33%.
[0012] Preferably, the weight ratio of the gravity center shifting
member to the shaft body is set to be in the range from 17% to 30%,
and more preferably, from 20% to 25%.
[0013] The gravity center shifting member may be provided with a
metal cylinder buried in an inner circumferential surface of the
shaft body.
[0014] The shaft body may be configured to include a first region
having a shaft outer diameter relatively gently reduced, a second
region having the shaft outer diameter relatively steeply reduced,
and a third region having the smallest relative change amount of
the shaft outer diameter, which are sequentially arranged from the
proximal-end side toward the distal-end side in the longitudinal
direction.
[0015] It is possible to set an occupancy percentage of the first
region in the longitudinal direction to 30% or higher, an occupancy
percentage of the second region in the longitudinal direction to be
in a range from 45% to 60%, and an occupancy percentage of the
third region in the longitudinal direction to be in a range from
10% to 25%.
[0016] It is possible to attach a grip to an outer circumferential
surface of the first region, and bury a metal cylinder as the
gravity center shifting member in an inner circumferential surface
of the third region.
[0017] The golf club according to the embodiment may be configured
to have a club head and a grip attached to any one of the golf club
shafts as described above.
[0018] The present invention ensures to provide the golf club shaft
and the golf club for offering excellent feel of swing motions
without demanding the fine setting while keeping advantages of the
short-sized golf club shaft.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 illustrates an example of an external appearance of a
golf club structure according to an embodiment.
[0020] FIG. 2 illustrates an example of a schematic structure of a
golf club shaft according to the embodiment.
[0021] FIG. 3 illustrates in an enlarged view an abutted part
between a shaft body and a metal cylinder, which is encircled in
FIG. 2.
[0022] FIG. 4 is a view of the golf club shaft illustrated by FIG.
2 when seen from a distal-end side.
[0023] FIG. 5 represents properties of three samples of the golf
club shaft according to the embodiment.
[0024] FIG. 6 represents an example of change in a shaft outer
diameter of the golf club shaft in the longitudinal direction
according to the embodiment.
[0025] FIG. 7 represents an example of each change in the shaft
outer diameter of the golf club shafts in the longitudinal
direction according to the embodiment and modified examples 1 to
3.
[0026] FIG. 8 represents an example of a laminated prepreg
structure constituting the shaft body.
DETAILED DESCRIPTION
[0027] FIG. 1 illustrates an example of an external appearance of a
structure of a golf club 10 according to an embodiment. The golf
club 10 includes a longitudinally extending golf club shaft 100, a
club head 200 attached to a distal-end side (tip side) of the golf
club shaft 100, and a grip 300 attached to a proximal-end side
(butt side) of the golf club shaft 100. FIG. 1 illustrates the club
head 200 formed as an iron club head. However, the club head 200
may be formed as a driver club head.
[0028] Referring to FIGS. 2 to 4, the schematic structure of the
golf club shaft 100 of the embodiment will be described. FIG. 2
illustrates the golf club shaft 100 having the shaft outer diameter
tapered from the proximal-end side (butt side) to the distal-end
side (tip side) at a constant taper ratio for convenience of making
the drawings. Actually, the shaft outer diameter of the golf club
shaft 100 is configured characteristically as described later
referring to FIG. 6.
[0029] The golf club shaft 100 includes a hollow cylindrical shaft
body 110 made of fiber reinforced resin, and a metal cylinder
(gravity center shifting member, weight) 120 attached to the
distal-end side of the shaft body 110.
[0030] The shaft body 110, for example, is made of FRP (Fiber
Reinforced Plastics) produced through thermosetting treatment of
multiple unset thermosetting resin prepregs, which have been
laminated and wound. The shaft body 110 (golf club shaft 100),
so-called short-sized shaft body (golf club shaft) is produced by
cutting the longitudinally extending shaft body 110 with its full
length of 43 inches or longer (for example, 45 inches or longer) in
the initial state to have the full length of 43 inches or shorter
in use. The cut length of the shaft body 110 at the proximal-end
side in the longitudinal direction is longer than the cut length of
the shaft body 110 at the distal-end side in the longitudinal
direction. The concept of the cut length applies to the case in
which the cut length of the shaft body 110 at the distal-end side
is zero. It is possible to cut the shaft body 110 only at the
proximal-end side without being cut at the distal-end side besides
the case of cutting both at the distal-end side and the
proximal-end side. The confirmation whether the shaft body 110 has
been cut for adjusting (reducing) the shaft full length may be made
by observing at least one of the distal-end surface and the
proximal-end surface of the shaft body 110.
[0031] The metal cylinder 120 is attached to the distal-end side of
the shaft body 110 for shifting the shaft gravity center (gravity
center position of the golf club shaft 100, balance point) toward
the distal-end side. The metal cylinder 120 is made of metal
material, for example, stainless steel, iron, aluminum, tungsten,
and the like. However, the metal cylinder may be made of any other
materials without restriction so long as the weight of the metal
cylinder is increased. Instead of using the metal cylinder 120, it
is possible to use the resin cylinder made of resin material, for
example, thermoplastic resin, thermosetting resin, rubber and the
like as the "gravity center shifting member, weight". Examples of
the thermoplastic resin include polypropylene, polyterephthalate,
polyethylene and the like. Examples of the thermosetting resin
include epoxy resin, phenol resin, unsaturated polyester resin,
polyurethane, polyimide, and the like. Examples of the rubber
include chloroprene rubber, fluororubber, chlorinated polyethylene,
nitrile rubber, isobutylene-isoprene rubber, ethylene-propylene
rubber, and the like.
[0032] As FIG. 3 illustrates, a burying recess cylindrical portion
112 is formed in an inner wall 111 of the shaft body 110 at an end
portion of the distal-end side. The metal cylinder 120 has its
outer radial portion buried in the burying recess cylindrical
portion 112 (the metal cylinder 120 is buried in the inner
circumferential surface of the shaft body 110). A proximal-end side
cylindrical end surface 121 of the metal cylinder 120 is brought
into abutment on a proximal-end side cylindrical end surface 113 of
the burying recess cylindrical portion 112 in the longitudinal
direction. The structure ensures to improve durability of the golf
club shaft 100 by preventing the metal cylinder 120 from falling
out from the shaft body 110 toward the proximal-end side even if
the impact is exerted upon swing or strike motions. The club head
200 attached to the end portion of the distal-end side of the shaft
body 110 prevents the metal cylinder 120 from falling out from the
shaft body 110 toward the distal-end side even if the impact is
exerted upon swing or strike motions.
[0033] Preferably, an abutment length A of an abutted area between
the proximal-end side cylindrical end surface 121 of the metal
cylinder 120 and the proximal-end side cylindrical end surface 113
of the burying recess cylindrical portion 112 is set to be in the
range from 0.05 mm to 0.5 mm. If the abutment length A is shorter
than 0.05 mm, there may be the case in which the metal cylinder 120
falls out from the shaft body 110 toward the proximal-end side when
the impact is exerted upon swing or strike motions. If the abutment
length A is longer than 0.5 mm, the shaft body 110 becomes so thin
that there may be the risk of dent, cut, and breakage of the fiber
reinforced resin layer of the shaft body 110 at the abutted area
between the proximal-end side cylindrical end surface 121 of the
metal cylinder 120 and the proximal-end side cylindrical end
surface 113 of the burying recess cylindrical portion 112.
[0034] As FIGS. 3 and 4 illustrate, a distal-end side cylindrical
end surface 122 of the metal cylinder 120 is exposed from a shaft
distal-end side end surface 114 of the shaft body 110. It is
possible to confirm whether the metal cylinder 120 is buried at the
shaft distal-end side by visually observing the shaft distal-end
side end surface 114 of the shaft body 110. This allows the metal
cylinder 120 to perform the function of shifting the gravity center
of the golf club shaft 100 toward the shaft distal-end side.
[0035] It is assumed that the golf club shaft 100 of the embodiment
has the shaft body 110 which has been cut to have its full length
of 43 inches or shorter, and positions of the distal-end portion
and the proximal-end portion of the shaft body 110 are defined by
percentage as 0% and 100% in the longitudinal direction,
respectively. The shaft gravity center which has been shifted by
the metal cylinder 120 is positioned in the range from 39% to 45%.
Assuming that the positions of the distal-end portion and the
proximal-end portion are defined by percentage as 0% and 100% in
the longitudinal direction, respectively, preferably, the shaft
gravity center which has been shifted by the metal cylinder 120 is
positioned in the range from 41% to 44%, and more preferably, from
42.5% to 43.5%.
[0036] By setting the position of the shaft gravity center which
has been shifted by the metal cylinder 120 to be in the
above-described range, various parameters of the golf club shaft
100 such as weight, frequency, and torque may be easily adjusted.
The structure allows excellent feel of swing motions without
requiring fine setting while keeping advantages of the short-sized
golf club shaft 100.
[0037] When the shaft gravity center shifted by the metal cylinder
120 is positioned closer to the distal-end side than the position
corresponding to 39% (below the lower limit of condition formula),
it is difficult to adjust the various parameters of the golf club
shaft 100 such as weight, frequency, and torque.
[0038] When the shaft gravity center shifted by the metal cylinder
120 is positioned closer to the proximal-end side than the position
corresponding to 45% (in excess of the upper limit of condition
formula), it is difficult to eliminate disadvantages as a result of
using the short-sized golf club shaft 100 (unnatural sense of swing
motions, difficulty in rise-up of the ball). Increase in the weight
of the club head for eliminating the disadvantages may cause the
risk of demanding the fine setting including adjustment of full
length of the short-sized golf club shaft.
[0039] The shaft gravity center of the generally employed
short-sized shaft body (golf club shaft) is positioned closer to
the proximal-end side than the position corresponding to 48% or 50%
(in excess of the upper limit of condition formula
significantly).
[0040] FIG. 5 represents properties of three samples of the golf
club shaft 100 according to the embodiment. As FIG. 5 represents,
samples 1, 2, 3 are prepared, each having its full length of 43
inches or longer in the initial state (for example, 45 inches or
longer), and different properties. Each of the samples 1 to 3 has
its shaft proximal-end side and shaft distal-end side partially cut
so that the cut amount of the shaft at the proximal-end side is
larger than that of the shaft at the distal-end side. Each position
of the shaft gravity centers of the respective samples is monitored
in each case of the shaft full lengths of 43 inches, 42 inches, 41
inches, and 40 inches, respectively.
[0041] In the case of the sample 1, when the shaft full length is
43 inches, the position of the shaft gravity center is set to
40.5%, when the shaft full length is 42 inches, the position is set
to 40.2%, when the shaft full length is 41 inches, the position is
set to 39.9%, and when the shaft full length is 40 inches, the
position is set to 39.6%.
[0042] In the case of the sample 2, when the shaft full length is
43 inches, the position of the shaft gravity center is set to
42.6%, when the shaft full length is 42 inches, the position is set
to 42.3%, when the shaft full length is 41 inches, the position is
set to 42.0%, and when the shaft full length is 40 inches, the
position is set to 41.7%.
[0043] In the case of the sample 3, when the shaft full length is
43 inches, the position of the shaft gravity center is set to
44.4%, when the shaft full length is 42 inches, the position is set
to 44.1%, when the shaft full length is 41 inches, the position is
set to 43.8%, and when the shaft full length is 40 inches, the
position is set to 43.5%.
[0044] In the embodiment, the weight ratio of the metal cylinder
120 to the shaft body 110 of the golf club shaft 100 is set to be
in the range from 14% to 33%. It is preferable to set the weight
ratio of the metal cylinder 120 to the shaft body 110 to be in the
range from 17% to 30%, and more preferably, from 20% to 25%.
[0045] By setting the weight ratio of the metal cylinder 120 to the
shaft body 110 to be in the above-described range, various
parameters of the golf club shaft 100 such as weight, frequency,
and torque may be easily adjusted. Facilitating the gravity center
shifting effect of the metal cylinder 120 allows easy setting of
the shaft gravity center position to be in the range from 39% to
45%.
[0046] If the weight ratio of the metal cylinder 120 to the shaft
body 110 is higher than 33% (in excess of the upper limit of
condition formula), it is difficult to adjust various parameters of
the golf club shaft 100 such as weight, frequency, and torque.
[0047] If the weight ratio of the metal cylinder 120 to the shaft
body 110 is lower than 14% (below the lower limit of condition
formula), it is difficult to obtain the gravity center shifting
effect of the metal cylinder 120. For example, it is difficult to
set the shaft gravity center to be positioned in the range from 39%
to 45%.
[0048] In the case of the sample 1, when the shaft full length is
43 inches, the weight ratio of the metal cylinder 120 to the shaft
body 110 is set to 29.8%, when the shaft full length is 42 inches,
the weight ratio is set to 30.5%, when the shaft full length is 41
inches, the weight ratio is set to 31.4%, and when the shaft full
length is 40 inches, the weight ratio is set to 32.2%.
[0049] In the case of the sample 2, when the shaft full length is
43 inches, the weight ratio of the metal cylinder 120 to the shaft
body 110 is set to 22.1%, when the shaft full length is 42 inches,
the weight ratio is set to 22.7%, when the shaft full length is 41
inches, the weight ratio is set to 23.3%, and when the shaft full
length is 40 inches, the weight ratio is set to 24.0%.
[0050] In the case of the sample 3, when the shaft full length is
43 inches, the weight ratio of the metal cylinder 120 to the shaft
body 110 is set to 18.1%, when the shaft full length is 42 inches,
the weight ratio is set to 18.6%, when the shaft full length is 41
inches, the weight ratio is set to 19.2%, and when the shaft full
length is 40 inches, the weight ratio is set to 19.8%.
[0051] FIG. 6 represents an example of change in the shaft outer
diameter (O.D. (mm)) of the golf club shaft 100 in the longitudinal
direction (X(mm)) according to the embodiment. The data of FIG. 6
have been acquired after cutting the shaft body to have its full
length of 43 inches or shorter.
[0052] As FIG. 6 represents, the shaft body 110 includes a first
region A1, a second region A2, and a third region A3 sequentially
arranged from the proximal-end side toward the distal-end side in
the longitudinal direction. In the first region A1, the shaft outer
diameter of the shaft body 110 is relatively gently reduced from
the proximal-end side toward the distal-end side in the
longitudinal direction. In the second region A2, the shaft outer
diameter of the shaft body 110 is relatively steeply reduced from
the proximal-end side toward the distal-end side in the
longitudinal direction. In the third region A3, the relative change
amount of the shaft outer diameter of the shaft body 110 becomes
the smallest in the longitudinal direction (substantially
straight). The grip 300 is attached to the outer circumferential
surface of the first region A1 of the shaft body 110. The metal
cylinder 120 is buried in the inner circumferential surface of the
third region A3 of the shaft body 110.
[0053] Preferably, each occupancy percentage of the first region
A1, the second region A2, and the third region A3 in the
longitudinal direction satisfies the following condition formulae.
That is, preferably, the occupancy percentage of the first region
A1 in the longitudinal direction is 30% or higher, the occupancy
percentage of the second region A2 in the longitudinal direction is
in the range from 45% to 60%, and the occupancy percentage of the
third region A3 in the longitudinal direction is in the range from
10% to 25%. Referring to the example of FIG. 6, the occupancy
percentage of the first region A1 in the longitudinal direction is
set to 32%, the occupancy percentage of the second region A2 in the
longitudinal direction is set to 50%, and the occupancy percentage
of the third region A3 in the longitudinal direction is set to
18%.
[0054] By setting the occupancy percentage of the first region A1
in the longitudinal direction to 30% or higher, the first region A1
may be secured as an attachment region of the grip 300. When
holding the grip 300 with both left and right hands, if the region
to be held with the right hand is thinner than the region to be
held with the left hand, the grip 300 is held with the right hand
under the grasping power stronger than needed. This may raise the
probability of making a miss shot.
[0055] By setting the occupancy percentage of the gently tapered
first region A1 to 30% or higher to secure the attachment region of
the grip 300, each thickness of the regions held with both left and
right hands is made substantially the same. This may prevent the
grip 300 to be held with the right hand from bearing the grasping
power stronger than needed, raising the probability of making a
nice shot.
[0056] On the contrary, if the occupancy percentage of the first
region A1 in the longitudinal direction is set to be lower than
30%, the attachment region of the grip 300 extends across the first
region A1 and the second region A2. This may make the region to be
held with the right hand thinner than the region to be held with
the left hand. The grip 300 to be held with the right hand bears
the grasping power stronger than needed, resulting in raised
probability of making the miss shot.
[0057] By setting the occupancy percentage of the third region A3
in the longitudinal direction to be in the range from 10% to 25%,
the third region A3 may be secured as a burying region of the metal
cylinder 120, and various parameters of the golf club shaft 100
such as weight, frequency, and torque may be easily adjusted.
[0058] As described above, the metal cylinder 120 is buried in the
inner circumferential surface of the third region A3 of the shaft
body 110. If the occupancy percentage of the third region A3 in the
longitudinal direction is lower than 10%, it is difficult to secure
the third region A3 as the burying region of the metal cylinder
120.
[0059] If the occupancy percentage of the third region A3 in the
longitudinal direction is higher than 25%, it is difficult to
adjust various parameters of the golf club shaft 100 such as
weight, frequency, and torque.
[0060] By setting the occupancy percentage of the second region A2
in the longitudinal direction to be in the range from 45% to 60%,
excellent sense (feeling) of strike motions may be obtained. This
also makes it possible to secure the first region A1 as the
attachment region of the grip 300, and the third region A3 as the
burying region of the metal cylinder 120.
[0061] If the occupancy percentage of the second region A2 in the
longitudinal direction is lower than 45%, the taper ratio (diameter
reduction degree) of the golf club shaft 100 (shaft body 110)
becomes too steep. This may cause the risk of making the sense
(feeling) of strike motions unnatural.
[0062] If the occupancy percentage of the second region A2 in the
longitudinal direction is higher than 60%, the first region A1
cannot be secured as the attachment region of the grip 300, and/or
the third region A3 cannot be secured as the burying region of the
metal cylinder 120.
[0063] FIG. 7 represents an example of change in each of the shaft
outer diameters in the longitudinal direction of the golf club
shaft 100 of the embodiment, and golf club shafts of comparative
examples 1 to 3. The explanation on the change in the shaft outer
diameter of the golf club shaft 100 of the embodiment has been made
with reference to FIG. 6. By contrast, each of the golf club shafts
of the comparative examples 1 to 3 is not divided into regions such
as the first region A1, the second region A2, and the third region
A3. Each of the regions has its diameter reduced from the
proximal-end side toward the distal-end side with substantially the
constant taper ratio across the entire region in the longitudinal
direction.
[0064] A deformed mandrel (not illustrated) is prepared for
manufacturing the above-described golf club shaft 100. An outer
radial configuration of the mandrel includes a gently tapered
surface (for example, taper ratio of 5/1000) for forming the first
region A1, a steeply tapered surface (for example, taper ratio of
13/1000) for forming the second region A2, and a substantially
straight surface for forming the third region A3. Then the inner
circumferential surface of the metal cylinder 120 is fitted with
the substantially straight surface of the deformed mandrel.
Multiple prepregs are laminatingly wound on the outer
circumferential surface of the deformed mandrel and the metal
cylinder 120. The multiple prepregs are thermally cured to form the
golf club shaft 100 having the shaft body 110 and the metal
cylinder 120 integrated. Finally, the deformed mandrel is pulled
out from the golf club shaft 100 for removal.
[0065] FIG. 8 represents an example of the laminated prepreg
structure which forms the shaft body 110. The laminated prepreg
structure is constituted by laminating carbon prepregs P1 to P8 in
this order on the upper layer of the metal cylinder 120. Each of
the carbon prepregs P1, P4 is a 0.degree. prepreg having its long
fiber direction parallel to the shaft longitudinal direction, and
is disposed partially on the distal-end side in the longitudinal
direction as a partial prepreg. Each of the paired carbon prepregs
P2, P3 is a full-length bias prepreg having its long fiber
direction at an angle of +/-45.degree. to the shaft longitudinal
direction, and extending across the entire longitudinal length.
Each of the carbon prepregs P5 to P7 is a 0.degree. prepreg having
its long fiber direction parallel to the shaft longitudinal
direction, and extending across the entire longitudinal length as a
full-length prepreg. The carbon prepreg P8 is a 0.degree. prepreg
having its long fiber direction parallel to the shaft longitudinal
direction, and wound on the deformed mandrel at the distal-end
side, serving as a reinforced prepreg. The laminated prepreg
structure as represented by FIG. 8 is one of exemplary cases. The
number or each structure of the laminated prepregs may be variously
modified.
[0066] Advanced golf players participated in the trial shot testing
as testers requested to use the golf club shaft 10 of the
embodiment, and a golf club shaft formed by attaching a heavier
club head to the generally employed short-sized golf club shaft.
Most of the testers felt that the sense (feeling) of strike motions
when using the golf club shaft 10 of the embodiment was better than
the use of the comparative one.
[0067] In the embodiment, the explanation has been made with
respect to the use of the metal cylinder 120 buried in the inner
circumferential surface of the shaft body 110 as the "gravity
center shifting member, weight" for adjusting the position of the
shaft gravity center. The "gravity center shifting member, weight"
may be embodied into an arbitrary form with the degree of freedom
as well as various modifications of design. For example, the metal
containing prepreg may be contained in the prepregs constituting
the shaft body 110 so that the resultant prepreg structure serves
as the "gravity center shifting member, weight" for adjusting the
position of the shaft gravity center. The laminated prepreg
structure constituting the shaft 110 may be arbitrarily devised to
serve as the "gravity center shifting member, weight" for adjusting
the position of the shaft gravity center.
[0068] The golf club shaft and the golf club according to the
embodiment, for example, for golf players, are suitable for
offering excellent feel of swing motions without demanding the fine
setting while keeping advantages of the short-sized golf club
shaft.
[0069] While the present disclosure has been illustrated and
described with respect to a particular embodiment thereof, it
should be appreciated by those of ordinary skill in the art that
various modifications to this disclosure may be made without
departing from the spirit and scope of the present disclosure.
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