Note: Descriptions are shown in the official language in which they were submitted.
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Golf Club Shaft Having Wave Shaped Reinforced Part
This application is a continuation-in-part of Serial No. 29/061,700 filed on
29 October
1996 and Serial No. 08/760,079 filed on 4 December 1996. This application
claims the
benefit of U.S. Provisional Application No. 60/047,697 filed on 23 May 1997.
BACKGROUND OF THE INVENTION
Since a carbon (graphite) shaft is lighter than a conventional steel shaft,
the head
speed of a golf club while swinging is increased, thus increasing the flying
distance of a ball
struck by the golf club. However, a graphite shaft has a disadvantage in that
its torsion
characteristics are poor. If the torsion characteristics of the shaft are
poor, the sweet spot of
the club head typically does not strike the ball during impact. When the ball
is impacted by
areas of the club head other than the sweet spot, the direction of the ball in
flight is not exact.
According to conventional methods for improving torsion characteristics of a
shaft,
first, the fiber orientation (angle formed by the axis of the shaft with the
textile tissue of
carbon fiber within prepreg sheet) of torsion layer should be f45 ° and
the prepreg sheets are
used for rolling the shaft several times; however, this method has
disadvantages in that flex
strength is significantly reduced and the weight of the shaft is increased,
even though torsion
characteristics are improved.
Second, steel or aluminum alloy is installed internally and on top of it,
prepreg sheets
are laminated in such a manner that the textile tissue of carbon fiber (mesh)
is at the same
position as
the axial direction of the shaft; however, the use of steel-type internal
conduit may be
responsible for increasing weight, thus adversely affecting the light weight
of a carbon shaft.
Meantime, for the improvement of flying distance of a golf ball, much research
has
focused on the enhancement of golf club head shape and material instead of the
golf club
shaft. However, the shaft is one of the important factors which influences the
flying distance
of a golf ball. The relevant conventional methods are as follows:
Korean Patent Open-Laid No. 95-23427 describes a method of providing some
reinforced lines within the shaft but this method has some disadvantages in
that the weight of
shaft increases.
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Korean Patent Open-Laid No. 96-1936 describes a method of forming the hollow
part
within the shaft with a hexagon or octagon but its manufacturing process is
very complicated
over the enhanced effects of flying distance.
Although these methods of the prior art provide shafts which may be used in
golf
clubs, these shafts suffer from the disadvantages described above. A need
therefore exists for
golf club shafts and golf clubs which overcome disadvantages such as those
described above.
SUMMARY OF THE INVENTION
The present invention relates to a golf club shaft comprising a base shaft
having an
internal surface and an external surface, and at least one wave shaped
reinforced part on at
least one of the surfaces wherein the wave shaped reinforced part has a
plurality of
reinforcement pieces. The wave shaped reinforced part is located on at least
one of the upper
portion, midpoint or lower portion.
The golf club shafts of the present invention can be made by applying a base
section
of a prepreg sheet or assembly having a plurality of finger like elements to a
portion of a base
shaft, wrapping the finger like elements around the base shaft to provide a
wave shaped
reinforced part having a plurality of reinforcement pieces, and curing the
shaft having the
wave shaped reinforced part thereon to produce a golf club shaft having a wave
shaped
reinforced part thereon.
Golf clubs made with the golf club shafts having at least one wave shaped
reinforced
part impart greater flying distance and/or directional accuracy to golf balls
struck with the
golf clubs. The wave shaped reinforced part improves the torsion
characteristics of the golf
club shaft and provides a means of changing the location of the kick point of
the shaft to
achieve a desired effect on flying distance and/or directional accuracy. The
present invention
provides a convenient means of adjusting the characteristics of a golf club
shaft according to
the skill level of the intended user.
Having summarized the invention, the invention will now be described in detail
by
reference to the drawings, detailed description and non-limiting examples.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a front view of a golf club shaft in accordance with a first
embodiment of the
invention in which a wave-shaped reinforced part is provided at the lower part
of the shaft.
Fig. 2 is a front view of a golf club shaft in accordance with a second
embodiment of
the invention in which a wave-shaped reinforced part is provided at the upper
part of the shaft
below the grip end.
Fig. 3 is a front view of a golf club shaft in accordance with a third
embodiment of the
invention in which wave-shaped reinforced parts are provided at both the lower
part and the
upper part of the shaft.
Fig. 4 is a front view of a golf club shaft in accordance with a fourth
embodiment of
the present invention in which a wave-shaped reinforced part is provided at
the middle part of
the shaft.
Fig. 5 is a front view of a golf club shaft in accordance with a fifth
embodiment of the
present invention in which a wave-shaped reinforced part is provided at a
location midway
between the grip end of the shaft and the middle point of the shaft.
Fig. 6 is a partial Longitudinal sectional view of a portion of the shaft
according to the
invention having a wave shaped reinforcement part that has a sinusoidal
configuration.
Fig. 7 shows frontal views of other possible shapes of waves of wave shaped
reinforcement parts useful in the invention.
Fig. 8 shows the preparatory state of forming the wave shaped reinforced part
before
wrapping finger like elements of the prepreg sheet around the shaft. The base
section of the
prepreg sheet or assembly is attached to the base shaft and the finger like
elements are shown
in an extended state.
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Fig. 9 is a perspective view of a section of a reinforced part of a golf club
shaft
according to the invention prior to curing of a wave shaped reinforced part
showing some of
the finger like elements of a prepreg sheet wound around the base shaft to
form reinforcement
pieces. Fig. 9 also shows some of the finger like elements in an extended
state prior to
winding around the base shaft.
Fig. 10 shows shaped reinforcement pieces that are formed by wrapping the
finger like
elements of the prepreg sheet around the shaft. One of the finger like
elements is shown in an
extended state to illustrate the effect of forming the finger like elements.
The figure also
shows a view of tape that is wrapped around the reinforcement pieces prior to
curing.
Fig. 11 shows a golf club shaft having a wave shaped reinforcement part that
partially
encircles a base shaft.
Fig. 12 shows a golf club shaft that has rib shaped reinforcement pieces.
Fig. 13 shows a golf club shaft having a wave shaped reinforcement piece on
the
interior of the shaft.
Fig. 14 is a frontal view of a golf club made with a first embodiment of a
golf club
shaft of the invention in which a wave-shaped reinforced part is provided at
the lower part of
the base shaft above the hosel.
Fig. 1 S is a frontal view of a golf club made with a second embodiment of a
golf club
shaft of the invention in which a wave-shaped reinforced part is provided at
the upper part of
the shaft below the grip.
Fig. 16 is a frontal view of a golf club made with a third embodiment of a
golf club
shaft of the invention in which wave-shaped reinforced parts are provided at
both the lower
part and the upper part of the shaft.
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Fig. 17 shows a golf club made with a fourth embodiment of a golf club shaft
of the
invention in which a wave-shaped reinforced part is located at the midpoint of
a base shaft.
Fig. 18 shows a golf club made with a fifth embodiment of a golf club shaft of
the
invention in which a wave-shaped reinforced part is located between the
midpoint and the
grip end of the shaft.
DETAILED DESCRIPTION OF THE INVENTION
Fig. 1 shows a first embodiment of the golf club shaft 25A of the present
invention, in
which a wave shaped reinforced part 1 is formed in the lower portion of the
golf club shaft.
The lower portion of the shaft that portion between the midpoint of the entire
length of the
shaft and the upper edge 12 of the hosel section. Fig. 1 shows the preferred
location a of the
reinforced part near hosel section P5. The wave shaped part 1, however, may be
located at
other positions between the upper edge of the hosel section and the midpoint
of the lower
portion of the shaft. When wave shaped reinforced part 1 is provided at
location a of base
shaft 5, there is a signif cant improvement in torsion characteristics of the
golf club shaft.
The wave shaped reinforced parts of the golf club shafts of the present
invention are
made up of reinforcement pieces. In wave shaped reinforced part 1, the number
of
reinforcement pieces is I to 6 reinforcement pieces, more preferably 1 to 3
reinforcement
pieces. Although a larger number of reinforcement pieces may be applied to the
shaft, it is
preferred to use at most 6 pieces to minimize the possibility that the weight
of the golf club
shaft may become excessive and thus reduce the flying distance of the ball.
Typically, when the number of reinforcement pieces in wave shaped reinforced
part 1
is 3 pieces, about 10 percent improvement in torsion characteristics may be
expected. As a
result, even though the ball is not hit by the sweet spot of the golf club
head during impact,
the ball generally goes in the desired direction and a bad hook or slice is
prevented. Also,
when wave-shaped reinforced part 1 is provided at the lower part a of base
shaft 5, the kick
point moves upward.
The length of wave shaped reinforced part 1 is about 2 cm to about 15 cm,
preferably
about 3 cm to about 10 cm.
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Fig. 2 shows a second embodiment of the invention in which a wave shaped
reinforced part 1' is provided in the upper portion of the golf club shaft.
The upper portion of
the golf club shaft is that portion between the midpoint of the entire length
of the shaft and
the lower edge of the grip section of the shaft. Fig. 2 shows the preferred
location b of the
wave shaped reinforced part near grip section 22. However, the wave shaped
reinforced part
1' may be located at other positions between the midpoint of the upper portion
of shaft and
the lower edge of the grip section. When wave-shaped reinforced part 1' is
provided at
location b, the kick point of golf club shaft 25B moves down, away from the
grip end 20.
The total length of wave shaped reinforced part 1' can range from about 2 cm
to about
20 cm, preferably about 3 cm to 15 cm. In wave shaped reinforced part 1', the
number of
reinforcement pieces is 1 to 7 reinforcement pieces, more preferably 3 to 5
reinforcement
pieces. Although a larger number of reinforcement pieces may be applied to the
shaft, it is
preferred to use no more than 7 pieces to minimize the possibility that the
weight of the golf
club shaft may become excessive and thus reduce the flying distance of the
ball.
Generally, if the kick point is located closer to the grip end of the shaft,
the flying
distance of the ball is enhanced but the direction of the ball is less
accurate. In addition, it
may become very difficult to make a swing that will produce exact impact at
the point where
the force of shaft is maximized, creating much difficulty for amateur golfers.
However, since golf club shafts such as the shaft illustrated in Fig. 2, cause
the kick
point to move down, the golf club shafts of the invention overcome the
aforementioned
shortcomings so as to make an exact swing and impact much easier even for
amateur golfers.
In addition, any loss of flying distance produced by the move-down of the kick
point can be
countered by extending the length of the base shaft 5. The length of base
shaft 5 therefore can
be increased to cause the kick point of the resulting golf club shaft to have
the same height
(from tip 10 of the shaft) as the original height of the kick point on base
shaft 5 prior to
forming the wave shaped reinforced part thereon so that the flying distance of
the ball
increases.
Without wishing to be bound by theory, the following Table 1 shows typical
percentages of movement of the kick point which may be expected depending on
the number
of reinforcement pieces in a wave shaped reinforced part when applied to
location b of a base
3 0 shaft.
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TABLE 1
NUMBER OF PERCENTAGE OF MOVEMENT OF THE KICK POINT
REINFORCEMENT (the percent decrease in the height of the
kick point measured
PIECES from the club head tip of the shaft)
3 3%
5%
7 7%
Thus, if the height of the kick point of a base shaft (measured from the club
head tip 10) is 15
cm without a wave shaped reinforced part 1', then forming a wave shaped
reinforced part
having 3 reinforcement pieces at the upper part b of the base shaft moves the
kick point
"down" to a height 14.5 cm (measured from club head tip 10). This is a 3%
decrease in height
from the original height of the kick point of the base shaft.
1 S Fig. 3 shows a third embodiment of the invention in which wave shaped
reinforced
parts 1 and 1' are located at both the lower and upper portions of the golf
club shaft. Fig. 3
shows the wave shaped reinforced part at the preferred location a near hosel
section 15 and
the preferred location b near grip section 22 respectively of base shaft 5.
However, part 1 may
be located at other positions between the midpoint of the lower portion of the
shaft and the
upper edge of the hosel section 15. Likewise, part 1' may be located at other
positions
between the midpoint of the upper portion of the shaft and the lower edge of
the grip section.
When reinforced parts 1 and 1' are provided at both location a and location b
of the base
shaft 5, improvement of ball flight direction may be expected together with a
more
convenient and exact swing.
In this embodiment, the total number of reinforcement pieces in wave shaped
reinforced parts 1 and 1' is 5 to 7 pieces. The wave shaped reinforced part 1'
located at upper
part b preferably has a larger number of reinforcement pieces than wave shaped
reinforced
part 1 located at lower part a. Reinforced part 1 typically has 2 to 3 pieces
and a length of
about 2 cm to about 8 cm. Wave shaped reinforced part 1' typically has 4 to 5
pieces and a
length of about 10 cm to about I S cm.
When wave shaped reinforced parts 1 and 1' are provided as described in this
embodiment, improvement of ball flight direction also may be expected together
with a more
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convenient and exact swing. Also, the direction of the kick point moves down
relative to the
kick point of the base shaft.
Fig. 4 shows a fourth embodiment of the present invention, in which a wave
shaped
reinforced part lA is provided at midpoint m of the length of the base shaft
5. If the wave
shaped reinforced part lA is provided at midpoint m, the kick point moves down
relative to
the location of the kick point of the base shaft 5.
In this embodiment, reinforced part lA typically has 5 to 7 pieces and a
length of 2
cm to about 20 cm, preferably about 3 cm to about 15 cm. When reinforced part
lA is
provided at midpoint m of base shaft 5, improvement of ball flight direction
also may be
expected together with a more convenient and exact swing.
The position of wave shaped reinforced part 1 A relative to midpoint m may
vary. For
example, wave shaped reinforcement part lA may be provided so as to cause wave
shaped
reinforced part lA to extend equally on each side of midpoint m. Wave shaped
reinforced
part lA also can be positioned to have unequal portions thereof extend on
either side of
midpoint m.
Fig. 5 shows a fifth embodiment of the present invention in which a wave
shaped
reinforced part 1 B is provided midway between the lower edge of grip section
22 and
midpoint m of the base shaft 5. In the golf club shaft shown in Fig. S, the
kick point moves
down relative to the location of the kick point of the original base shaft 5.
In this
embodiment, reinforced part 1B typically has 5 to 7 pieces and a length of
about 10 cm to
about 20 cm. When reinforced part 1 B is provided at midpoint m of base shaft
5,
improvement of ball flight direction also may be expected together with a more
convenient
and exact swing.
Fig. 6 is a partial cross sectional view of a portion of the shaft according
to the
invention having a wave shaped reinforced part that has a sinusoidal
configuration, i.e., the
surfaces of the waves are curved as opposed to an angular or compressed wave
configuration.
The reinforcement pieces of the wave-shaped reinforced parts of the golf club
shafts of the
invention preferably have a sinusoidal configuration as shown, for example, in
Fig. 6.
The shape of the waves formed by reinforcement pieces may have alternative
configurations such as, for example, square wave configuration, triangular
wave
configuration, compressed wave configuration, and trapezoidal configuration.
Examples of
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these alternative configurations are shown in Fig. 7 which shows frontal views
of other
possible configurations of wave shaped reinforced parts used in the invention.
BASE SHAFT
The base shafts that can be employed to make the golf club shafts of the
present
invention include, but are not limited to, commercially available graphite
shafts, titanium
shafts, steel shafts, fiberglass shafts and other shafts that are suitable for
use in making golf
clubs. Graphite shafts are preferred as the base shaft. The base shaft can be
in an unfinished
state, i.e., prior to application of finishing materials such as lacquers.
Finished shafts that
have been treated with finishing materials can also be used as the base shaft.
Many prior art golf club shafts such those disclosed in Korean Patent
Application No.
96-1939 require complicated manufacturing processes. An advantage of the
present invention
over golf club shafts of the prior art is that commercially available base
shafts can be used to
produce the golf club shafts according to the invention. The present invention
provides a
convenient means of moving the kick point of the golf club shafts according to
the skill level
I 5 of the intended user.
PREPREG SHEET STARTING MATERIAL
Prepreg is the composite industry's term for continuous fiber reinforcement
material
which is pre-impregnated with a partially cured polymer resin. Prepreg sheets
are well known
in the art. Prepreg sheets are produced by known methods such as that
disclosed in Callister,
William D., Materials Science and Engineering: An Introduction, John Wiley &
Sons, Inc,
N.Y. ( 1994) herein incorporated by reference. Commercially available prepreg
sheets can be
used to
form wave shaped reinforced parts of the golf club shaft according to the
invention.
Prepreg sheets useful in the invention include carbon fiber reinforced prepreg
sheets
wherein the carbon fibers run in a single direction. Glass fiber reinforced
prepreg sheets can
also be used wherein the glass fibers are woven to intersect each other in a
perpendicular
orientation forming a criss-cross pattern. In a preferred embodiment of the
invention, the
prepreg sheet starting material is an assembly of a glass fiber prepreg sheet
on top of a carbon
prepreg sheet so that the glass prepreg sheet is on the outside surface of the
reinforced part.
This type of assembly prevents the carbon fibers from leaking or peeling off
during the
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manufacturing process.
Prepreg sheets useful in the invention include but are not limited to those
which are
impregnated with a thermoplastic resin, preferably epoxy resin. The thickness
of the prepreg
sheet is typically between about 0. I mm to about 0.15 mm. An example of a
carbon fiber
prepreg sheet useful in the invention is known as T700 and was obtained
through Korea Fiber
Co. of Korea.
TOTAL WEIGHT OF GOLF CLUB SHAFT WITH REINFORCED PARTS)
The desired total weight of the golf club shaft with wave shaped reinforced
parts) is
an important factor in determining the appropriate thickness of the prepreg
sheet and the
thickness of the reinforcement pieces. Typical total weights of the golf club
shaft can range
from about 70g to about I OOg. It is preferred that the total weight of a golf
club shaft for a
driver in accordance with the invention which has three or more wave shaped
reinforced
parts is about 70g to about 75g. The preferred total weight for a golf club
shaft of the
invention which has three or more wave shaped reinforced parts, when used in a
5-iron, is
about 68g to about 72g.
PREPREG SHEET BASE SECTION AND FINGER LIKE ELEMENTS
Fig. 8 shows base section 2B of prepreg sheet 2A attached vertically onto a
portion
of base shaft 5. As illustrated in Fig. 8, prepreg sheet 2A has finger like
elements 2 that are
formed by removing sections from a prepreg sheet starting material. The base
section 2B of
prepreg
sheet 2A is attached to base shaft 5, and finger like elements 2 are shown in
a position for
wrapping around and onto base shaft 5. Generally, the length of base section
2B of a prepreg
sheet corresponds to the desired length of the wave shaped reinforced part.
As discussed in more detail below, prepreg sheet 2A can be made from a single
prepreg sheet or an assembly of prepreg sheets such as a glass fiber prepreg
sheet on top of a
carbon fiber prepreg sheet. The assembly is cut to form a prepreg sheet 2A
with finger like
elements 2.
The finger like elements 2 preferably have an elongated, tapered shape as
shown in
Fig. 8. Although it is preferred to use finger like elements 2 which have a
tapered shape,
finger like elements 2 may have a variety of shapes depending on the
configuration of the
waves desired in the wave shaped reinforced part. The shape of the finger like
elements 2
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may be readily determined by those of ordinary skill in the art depending on
the
configuration of the waves desired in the wave shaped reinforced part.
Finger tike elements 2 are formed by cutting a prepreg sheet or assembly by
known
means such as utility knives, carbide disk cutters, and the like. More
advanced cutting means
includes die cutting and laser cutting. In the example shown in Fig. 8, finger
like elements 2
are curved toward the grip end of the base shaft 5. This configuration is
useful to form
reinforcement pieces which yield a wave shaped reinforced part that has a
sinusoidal
configuration. The degree of curvature of the finger like elements used to
form a wave
shaped reinforced part that has a sinusoidal configuration can readily be
determined
according to the size and shape of a particular base shaft. For example, when
the base shaft
tapers in the direction of the club head tip of the base shaft, the length of
finger like elements
2 can be increased as the radius of the base shaft decreases toward the tip
end of the shaft.
SHAPE OF THE REINFORCEMENT PIECES
The outer shape of the reinforcement pieces which form a wave-shaped
reinforced
part can be formed according to the type of wave desired in the wave shaped
reinforced part.
For example, the reinforcement pieces may have a sinusoidal shape to provide a
wave
shaped reinforced part having a sinusoidal configuration as shown in Fig 6.
Similarly, the
reinforcement piece may have other shapes to provide wave shaped reinforced
parts which
have, for example, compressed wave configurations, triangular wave
configurations, square
wave configurations and the like as shown in Fig. 7. Other possible
configurations include
arc, tetragonal or spiral configurations. A particular configuration can be
formed by sanding
the waves to the desired configuration. A wave shaped reinforced part that has
a spiral form
can be formed, for example, by forming a "rope" from carbon fibers. The "rope"
is wound
spirally around a base shaft to form the desired number of reinforcement
pieces.
THICKNESS OF THE REINFORCEMENT PIECES
Fig. 9 shows a section of a golf club shaft having a wave shaped reinforced
part prior
to curing. Fig. 9 also shows finger like elements 2 extended prior to winding
around the
shaft. During manufacture, finger like elements 2 are wrapped around base
shaft 5 to form
reinforcement pieces 30 having thickness T and overall diameter D. The
thickness T of
reinforcement pieces such as those shown in Fig. 9 is a function of 1 ) the
desired total
weight of the golf club shaft with the wave shaped reinforced part and 2) the
taper of the
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shaft. The thickness T of the reinforcement pieces is at least about 0.5 mm.
Typically, the
maximum thickness of the~reinforcement pieces is about 1.5 mm to maintain the
total weight
of the golf club shaft within current commercially desirable weight limits.
In one embodiment of the golf club shaft of the invention, the overall
diameters D as
shown in Fig. 9 of the base shaft and reinforcement pieces in a wave shaped
reinforced part
are the same. In this embodiment, the thickness T of each reinforcement piece
can vary
depending on the taper of the shaft. For example, as the diameter of the base
shaft
decreases, the thickness T of reinforcement pieces can increase so that the
overall diameters
D of the base shaft and reinforcement pieces is constant. In another
embodiment, the
thicknesses of the reinforcement pieces is constant and the overall diameters
D of the base
shaft and the reinforcement pieces can vary.
MANUFACTURE AND ASSEMBLY
A golf club shaft of the invention is formed by bonding a prepreg sheet or,
preferably, a prepreg sheet assembly onto a base shaft. The prepreg sheet or
assembly
includes a base section and finger-like members joined to the base section.
The finger-Iike
members are wrapped around the base shaft to provide a wave shaped reinforced
part.
In one embodiment of the manufacture of the golf club shafts of the invention,
the
base section of a prepreg sheet or assembly having finger like elements 2 as
shown, for
example, in Fig. 8, is attached vertically along the length of a desired
section of a base shaft
24 by an adhesive such as epoxy resin. Finger like elements 2 are wrapped
around base shaft 5
to produce reinforcement pieces 30 such as those shown, for example, in Fig.
9.
Fig. 10 shows a section of a golf club shaft having a wave shaped reinforced
part wherein the reinforcement pieces are covered by tape 40 prior to curing.
Fig. 10 also
shows a finger like element 2 extended prior to winding around the shaft.
During
manufacture, finger like elements 2 are wrapped around base shaft to form
reinforcement
pieces 30 having thickness T and overall diameter D. The resulting wave shaped
reinforced
part can be covered with carbon tape 40 prior to curing as shown in Fig. 10.
The wave
shaped reinforced part is cured by heat at an appropriate temperature for the
particular
prepreg sheet. Generally, the curing temperature and time are functions of the
particular
prepreg sheet starting material. Curing temperatures and times are widely
known and
published for various prepreg sheets that can be used alone or in an assembly
in the present
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invention. One skilled in the art can readily determine the time and
temperature values for
the specific prepreg sheet being used, the length of the reinforced part, and
the number and
thickness of the reinforcement pieces. The time and temperatures can be
selected for full or
limited cure.
Although it is preferred to bond a prepreg sheet or assembly around a base
shaft as
described above, a wave shaped reinforced part having a sinusoidal
configuration shown in
Fig. 6 or any of the other configurations shown in Fig. 7 may be formed by
well known
techniques such as compression molding, flame spraying, plasma deposition and
the like.
In a first embodiment of a compression molding method useful in the invention,
one
or more layers of uncut prepreg sheet material is wrapped onto the surface of
the shaft. The
wrapped shaft then is compressed under heat and pressure in a mold having the
desired
configuration of the waves in the wave shaped reinforced part. Preferably, the
wave shaped
reinforced part such as reinforced part 1, 1' is formed on the exterior
surface of base shaft 5.
As an alternative to compression molding, techniques such as flame spraying
may be
employed to deposit material onto the surface of the shaft to yield a wave
shaped reinforced
part having a desired wave shape on selected portions of the base shaft.
Although it is preferred that the wave shaped reinforced part completely
encircle the
base
shaft as shown, for example, in Fig. 10, a wave shaped reinforced part 32 may
be formed on
selected portions of shaft 25I which only partially encircles the shaft as
shown in Fig. 11.
Wave shaped reinforced parts which only partially encircle the shaft may
readily be formed
by techniques such as compression molding and flame spraying. Techniques such
as
compression molding and flame spraying are especially suitable for forming a
golf club shaft
25F which has, for example, rib shaped reinforcement pieces 31 as shown in
Fig. 12.
Compression molding also may be used for example, to form a wave shaped
reinforcement pieces 30 on the internal surface of a base shaft 25G as shown
for example, in
Fig. 13. In this aspect, a rod having expandible sections may be inserted into
a base shaft.
The expandible sections of the rod then are compressed against the interior
surface of the
base shaft to form reinforcement pieces. Preferably, the reinforcement pieces
are wave
shaped to produce a wave shaped reinforced part that has a sinusoidal
configuration. Other
wave shapes, e.g., any of those shown in Fig. 7, may be made by compression
molding.
Fig. 14 shows a golf club made from a first embodiment of golf club shaft 25A
of the
present invention in which a wave shaped reinforced part 1 is located at the
lower part a of a
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base shaft 5 near hosel section 15. When wave shaped reinforced part 1 is
provided at the
lower part a of base shaft 5, there is a significant improvement in torsion
characteristics of
the golf club shaft.
Fig. 15 shows a golf club made from a golf club shaft 25B in accordance with a
second embodiment of the invention in which wave shaped reinforced part 1' is
located at
location b of the golf club shaft near the grip 27. When wave-shaped
reinforced part 1' is
provided at location b, the kick point of golf club shaft 25B moves down, away
from the
grip 27.
Fig. 16 shows a golf club made from a golf club shaft 25C in accordance with a
third embodiment of the invention in which wave shaped reinforced parts 1 and
I' are
located at location a and location b respectively of base shaft 5. When
reinforced parts 1 and
1' are provided at both location a and location b of the base shaft 5,
improvement of ball
flight direction may be expected together with a more convenient and exact
swing.
Fig. 17 shows a golf club 29D made from a golf club shaft 25D in accordance
with a
fourth embodiment of the invention in which a wave shaped reinforced part lA
is located at
the midpoint m of base shaft 5. When reinforced part lA is provided at
midpoint m of base
shaft 5, improvement of ball flight direction also may be expected together
with a more
convenient and exact swing.
Fig. 18 shows a golf club 29E made from a golf club shaft 25E in accordance
with a
fifth embodiment of the invention in which a wave shaped reinforced part 1B is
located
between midpoint m and the lower edge of grip 27 of base shaft 5. When
reinforced part 1B
is provided at midpoint m of base shaft 5, the kick point moves down and
improvement of
ball flight direction may be expected together with a more convenient and
exact swing.
The golf club shaft of the present invention has various advantages such as:
a)
improvement of torsion characteristics of the shaft, b) controllable movement
of the kick
point of the golf club shaft to a desired location to improve the direction of
a golf ball with a
more convenient and accurate swing, and c) the ability to further extend the
length of the
reinforced shaft to improve the flying distance of a golf ball without
application of added
force, i.e., without the need to employ a higher swing speed. Another
advantage is the ability
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to use of commercially available base shafts to produce the golf club shafts
of the present
invention thus avoiding the complicated manufacturing processes required by
golf club
shafts of the prior art.
Golf clubs made with the shafts of the present invention impart greater flying
distance and/or directional accuracy to golf balls struck by the golf clubs.
The reinforced
part provides a means of moving the kick point of the shaft to achieve a
desired effect on
flying distance and/or accuracy. The present invention also provides a
convenient means of
adjusting the characteristics of a golf club shaft according to the skill
level of the intended
user.
In addition, the wave-shaped reinforced part offsets the impact wave induced
when
impacting a ball, thus protecting the human body.
EXAMPLES
In an illustrative but non-limiting example, a commercially available carbon
fiber
prepreg sheet known as T700 obtained through Korea Fiber Company of Korea and
a
commercially available glass fiber prepreg sheet are placed together and then
the assembly is
cut to form a base
section with finger-like elements having curved edges as shown in Fig. 8. Base
section 2B of
the prepreg assembly is attached along the length of the desired section of
the base shaft by
epoxy resin and the finger-like elements are wrapped tightly around the base
shaft to form a
wave shaped reinforced part that has a sinusoidal wave configuration. The
resulting wave
shaped reinforced part is covered with carbon tape. The covered wave shaped
reinforced part
is then heat cured by placing the shaft having the wave shaped reinforced part
into an oven
at 80 °C and then raising the temperature to 120 °C over 30
minutes. Thereafter, the
temperature is raised to 130 °C over 60 minutes. The shaft having the
cured wave shaped
reinforced part thereon then is removed from the oven and cooled to room
temperature.
After curing is completed, the tape is removed by sandpaper, and the shaft is
ground to
remove any imperfections and to give the resulting wave shaped reinforced part
a smooth
finish. Grinding may also be employed to alter the shape of a reinforcement
piece or pieces
in the cured wave shaped reinforced part to achieve a desired wave
configuration.
In another non-limiting example of the invention, a golf club shaft such as
that
illustrated in Fig. 2 is produced. In this example, the golf club shaft
includes a base shaft
that has a weight of 62 gram, and total length of 1143 mm. The original kick
point is
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located 46 cm from the club head tip of the shaft. In accordance with the
invention, it is
found that after adding a wave shaped reinforced part having a length of 20 cm
and having 5
reinforcement pieces, the kick point moves down to 44 cm from the club head
tip of the
shaft. The weight of the shaft having the reinforced part, measured prior to
application of
finishing materials such as lacquers and the like, is 68 grams. If it is
desired to the same
height of kick point as the original base shaft prior to forming the
reinforced part thereon,
the length of the base shaft may be extended by about 70 mm to about 1 I 0 mm.
The following Tables 2-4 show measurements of carry, and of carry and roll
distances (in yards) for a golf club made from a commercially available golf
club shaft
("CONTROL") and the same type of golf club made from a golf club shaft
according to the
invention ("INVENTION"). The specifications of the Test Clubs were comparable.
The
clubs were tested in a mechanical swinging device wherein the club head speed
was 95mph.
CONTROL
Test Club Head: Tour Edge Titanium 950-Driver (9.0°)
Club Shaft: Aldila - R/S Flex
INVENTION
Test Club Head: Tour Edge Titanium 950-Driver
Club Shaft: Golf club shaft according to the invention with the wave
shaped reinforced part having five reinforcement pieces near
the grip section. The upper edge of the reinforced part was
located around 2.5 inches below a 10 3/8 inch grip. The shaft
was made from a graphite base shaft that was 45 inches long.
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TABLE 2
CENTER HITS Carry Carry and
Roll
Distance Accuracy Distance Accuracy
(yds) (yds)
CONTROL 235.0 -0.8 281.8 -6.0
Std. Dev. 1.4 4.5 7.4 6.4
INVENTION 244.0 2.4 272.8 2.4
Std. Dev. 3.5 4.5 3.6 4.2
TABLE 3
'/Z TOE HITS Carry Carry and
Roll
Distance Accuracy Distance Accuracy
(yds) (yds)
CONTROL 221.4 13.4 271.2 12.8
Std. Dev. 4.7 2.1 8.3 1.9
IS
INVENTION 240.0 2.4 268.8 0.3
Std. Dev. 1.9 2.2 4.8 2.9
TABLE 4
'/Z HEEL HITSCarry Carry and
Roll
Distance Accuracy Distance Accuracy
CONTROL 215.4 -18.8 265.0 -20.0
Std. Dev. 4.6 3.7
INVENTION 235.8 -27.6 271.0 -19.0
Std. Dev. 6.6 10.1 5.7 1.4
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