U.S. patent application number 09/745001 was filed with the patent office on 2002-06-27 for metal and composite golf club shaft.
Invention is credited to Cokeing, Scott D., Hedrick, Michael W., Horwood, Graeme, Thomas, James S., Walker, Michael D..
Application Number | 20020082111 09/745001 |
Document ID | / |
Family ID | 24994805 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020082111 |
Kind Code |
A1 |
Hedrick, Michael W. ; et
al. |
June 27, 2002 |
Metal and composite golf club shaft
Abstract
A golf club shaft is provided including a metal tip section and
a composite butt section. The butt section includes a reduced
diameter portion telescopically received within an axial bore of
the tip section. An adhesive is disposed between the tip section
and the butt section to secure the two together. An insulating
layer may be disposed between the tip section and the butt section
to prevent galvanic corrosion.
Inventors: |
Hedrick, Michael W.;
(Vyhalia, MS) ; Walker, Michael D.; (Memphis,
TN) ; Cokeing, Scott D.; (Eads, TN) ; Thomas,
James S.; (Barlett, TN) ; Horwood, Graeme;
(Germantown, TN) |
Correspondence
Address: |
Harness, Dickey & Pierce, P.L.C.
P.O. Box 828
Bloomfield Hills
MI
48303
US
|
Family ID: |
24994805 |
Appl. No.: |
09/745001 |
Filed: |
December 21, 2000 |
Current U.S.
Class: |
473/316 |
Current CPC
Class: |
A63B 53/12 20130101;
A63B 60/00 20151001; A63B 60/28 20151001; A63B 53/10 20130101 |
Class at
Publication: |
473/316 |
International
Class: |
A63B 053/10; A63B
053/12 |
Claims
What is claimed is:
1. A shaft comprising: a tip section formed of a metal material and
having a length between about 6 and about 12 inches and a diameter
at an upper end thereof between about .0.385 and about .0.415
inches; and a butt section formed of a composite material coupled
to said tip section.
2. The shaft of claim I wherein said tip section has a lower end, a
diameter of said lower end being about 0.335 inches or about 0.350
inches.
3. The shaft of claim 1 wherein said tip section has a wall
thickness between about 0.0125 and about 0.0175 inches.
4. The shaft of claim 1 wherein said butt section has a wall
thickness between about 0.025 and about 0.125 inches.
5. The shaft of claim 1 further comprising: an adhesive disposed
between said tip section and said butt section.
6. The shaft of claim 5 wherein said adhesive has a thickness
between about 0.003 and about 0.006 inches.
7. The shaft of claim 1 wherein said butt section has a plug
telescopically received within said tip section.
8. The shaft of claim 1 wherein said tip section overlaps said plug
over a length of about 0.75 to about 1.5 inches.
9. The shaft of claim 1 further comprising a plastic ferrule
disposed between said tip section and said butt section.
10. The shaft of claim 1 further comprising: an insulating layer
disposed between said tip section and said butt section.
11. The shaft of claim 10 wherein said insulating layer further
comprises one of a plurality of insulating spacers disposed between
said tip section and said butt section, and a glass layer formed as
an outboard part of said tip section so as to be located proximate
said butt section.
12. A shaft comprising: a tip section formed of a metal material;
and a butt section formed of a composite material and having a plug
extending from one end thereof telescopically received within said
tip section, said tip section overlapping said plug by a length
between about 0.75 and 1.5 inches.
13. The shaft of claim 12 wherein said tip section has a length
between about 6 and about 12 inches.
14. The shaft of claim 12 wherein said butt section has a wall
thickness between about 0.025 and about 0.125 inches.
15. The shaft of claim 12 wherein said tip section has a wall
thickness between about 0.0125 and about 0.175 inches.
16. The shaft of claim 12 wherein said tip section has an upper end
and a lower end, a diameter of said lower end being about 0.335
inches or about 0.350 inches.
17. The shaft of claim 12 wherein said tip section has an upper end
and a lower end, a diameter of said upper end being between about
0.385 inches and about 0.415 inches.
18. The shaft of claim 12 further comprising: an adhesive disposed
between said tip section and said butt section.
19. The shaft of claim 18 wherein said adhesive has a thickness
between about 0.003 and about 0.006 inches.
20. The shaft of claim 12 further comprising a plastic ferrule
disposed between said tip section and said butt section.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a golf club shaft having improved
performance characteristics and more particularly to a two piece
golf club shaft combining a metal portion and a composite portion
which retains the advantages of both materials while eliminating
their disadvantages.
[0002] Control and accuracy in the game of golf is influenced by
the torsional stiffness of the shaft. The torsional stiffness of
the shaft resists twisting of the club head during the swing and
particularly when there is less than perfect contact between the
golf ball and club head. Metal golf club shafts, the most popular
metal being steel, are used by many golfers. An advantage of steel
shafts is their high torsional stiffness which are known in the
relevant art as "low torque" shafts.
[0003] Many golf shaft manufacturers offer composite shafts, often
referred to as graphite shafts, which are usually made from a
composite of graphite or carbon fiber and epoxy resin. Composite
shafts can be significantly lighter than metal shafts, but the
torsional stiffness of a conventional graphite shaft is less than
that of a steel shaft. Graphite shafts are therefore known in the
art as `higher torque` than steel shafts.
[0004] In an attempt to torsionally stiffen composite shafts,
manufacturers have used different fiber types such as high modulus
carbon, aramid and boron fibers. They have also varied the
construction by wrapping the fibers at different angles in an
attempt to improve torsional stiffness. Most of these changes have
increased the cost and often had a negative effect on the
playability of the shaft.
[0005] Recent studies have shown that only the tip section of the
shaft provides the torsional resistance to prevent club head
twisting due to poor ball/head contact. Contact between the club
head and ball is a very brief dynamic event and only the tip
section of the shaft gets loaded during this time period. The event
is effectively over before the full length of the shaft is loaded.
It is therefore desirable to construct the tip section of the shaft
from metal which has a high torsional stiffness, such as steel,
whereas the butt section can be constructed from a composite, such
as graphite, with a lower torsional stiffness. In such a manner,
the effective torque characteristic of the shaft can be enhanced
while maintaining a light weight.
[0006] One attempt to combine the advantages of metal and composite
shafts is disclosed in U.S. Pat. No. 4,836,545 to Pompa. However,
Pompa does not describe the affect the physical characteristics of
the two shaft sections has on shaft performance. The length and
weight of the two sections of the Pompa shaft were arbitrarily
selected. Testing also revealed that the weight of the metal tip
section was extremely heavy as compared to the weight of the
composite butt section. By having a tip section that was too heavy,
the center of gravity (CG) of the shaft moved towards the tip end
and undesirably increased the swing weight of the club.
[0007] Swing weight is a measure of the static moment of the
assembled club about a point usually 14" from the grip end. The
absolute weight and balance point (CG position) of head, shaft and
grip all affect club swing weight. Although it is common for major
club manufacturers to specify head weights to achieve desired club
swing weights knowing the specifications of the shaft and grip,
this approach is not always possible. Component suppliers typically
offer club head weights which conform to industry accepted weight
ranges. As such, it is highly desirable to provide shafts that may
be used with such heads to achieve popular club swing weights.
[0008] Further, it is undesirable for the head to receive secondary
weighting to achieve a desired club swing weight. Secondary
weighting is usually introduced at the extreme tip end of the shaft
where the shaft is inserted in the hosel of the head. This
positioning is not optimal being away from the head center of
gravity and thus reduces momentum transfer to the ball for a given
swing speed. Less momentum transfer to the ball reduces the
distance the ball will travel.
[0009] Pompa also failed to appreciate the difficulty of joining
the metal and composite sections of the shaft. The joint must be
cosmetically acceptable and strong enough to prevent failure.
[0010] In view of the foregoing, it would be desirable to provide
an improved golf club shaft that exhibits the advantages of both
metal and composite shafts while eliminating their respective
disadvantages.
SUMMARY OF THE INVENTION
[0011] It is a primary purpose and principal objective of the
present invention to provide a golf club shaft combining the
separate advantages of metal and composite shafts into a single,
hybrid design.
[0012] It is another objective of the present invention to
eliminate the separate disadvantages of metal and composite shafts
in a single, hybrid design.
[0013] It is yet another objective of the present invention to
provide a method for manufacturing a golf club shaft having a tip
section of a metallic material and a butt section of a composite
material.
[0014] It is still yet another objective of the present invention
to provide a method and device for achieving the above objectives
while conforming to the rules of golf as defined by the United
States Golf Association.
[0015] According to one embodiment of the present invention, a golf
club shaft is provided including a metal tip section and a
composite buff section. The cylindrical tip section is formed of a
metallic material such as steel. The cylindrical butt section is
formed of a composite material such as graphite and includes a
reduced diameter portion or plug formed at an end thereof. The plug
of the butt section is telescopically received in the end of the
tip section such that the end of the tip section overlaps the
reduced diameter portion of the butt section. An adhesive, such as
epoxy, is disposed between the tip and butt sections to secure the
two sections together.
[0016] In another embodiment of the present invention, an
insulating layer is disposed between the tip and butt sections to
prevent metal to composite contact within the metal/composite
joint. By preventing metal to composite contact, the insulating
layer reduces or eliminates the potential for galvanic corrosion
within the joint. The insulating layer may be formed as a plurality
of insulating spacers such as glass beads or a glass layer built
into the butt section within the joint.
[0017] The invention will be better understood and further objects
and advantages thereof will become more apparent from the ensuing
detailed description taken in conjunction with the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 is a schematic side elevation view of a golf club
shaft incorporating the teachings of the present invention;
[0019] FIG. 2 is a graph showing the relationship of torsional
resistance to metal tip length;
[0020] FIG. 3 is a graph showing the relationship of torsional
resistance to metal and composite tip lengths;
[0021] FIG. 4 is a graph showing the relationship of shaft weight
to tip length and its affect on club swing weight;
[0022] FIG. 5 is a detailed schematic cross sectional view of a
metal/composite joint of the golf club shaft of FIG. 1;
[0023] FIG. 6 is a graph showing the relationship of the tip
bending stiffness of the shaft of the present invention to that of
a conventional steel shaft;
[0024] FIG. 7 is a graph showing the relationship of the tip wall
thickness of the shaft of the present invention to that of a
conventional steel shaft;
[0025] FIG. 8 is a graph showing the relationship of the butt wall
thickness of the shaft of the present invention to that of a
conventional graphite shaft;
[0026] FIG. 9 is a detailed schematic cross sectional view of a
metal/composite joint of the golf club shaft of FIG. 1 according to
a second embodiment of the present invention;
[0027] FIG. 10 is a detailed schematic cross sectional view of a
metal/composite joint of the golf club shaft of FIG. 1 according to
a third embodiment of the present invention; and
[0028] FIGS. 11a and 11b are detailed schematic cross sectional
views of a metal/composite joint of the golf club shaft of FIG. 1
according to a fourth embodiment of the present invention.
DETAILED DESCRIPTION
[0029] Referring to FIG. 1, there is shown a golf club 10 having a
grip 12, a head 14 and a tubular shaft 16. Although the club 10 is
illustrated as a wood, it may also be an iron or a putter. The
shaft 16 includes a tip section 18 and a butt section 20. The tip
section 18 is preferably formed of a metallic material such as high
strength steel while the butt section 20 is preferably formed of a
composite material such as graphite. While the shaft 16 has been
illustrated as having a smooth, tapered sidewall 22, it should be
appreciated that a parallel or stepped sidewall could substitute
therefore.
[0030] The tip section 18 is secured at a lower end 24 to head 14
by sizing it to fit standard club head hosel sockets. The upper end
26 of tip section 18 is telescopically and slidingly fit over the
lower end 28 of the butt section 20. The physical characteristics
of the tip section 18 from head 14 to the joint 30 where it meets
the butt section 20, are designed to provide desired balance of
torsional stiffness, bending stiffness (flex), strength, and weight
in order to yield the best playability when combined with the
composite butt section.
[0031] The relationship between the physical characteristics of the
tip 18 and the playability of the shaft 16 is complex and many
factors must be taken into consideration.
[0032] 1) As the metallic tip section 18 is shortened, the
torsional stiffness it provides becomes less significant. As the
tip section 18 is lengthened, the weight of the tip section 18
becomes more significant.
[0033] 2) It is desirable to retain an industry standard diameter
of either 0. 335 or 0.350 inches at the lower end 24 of the tip
section 18 to allow fitment of industry standard club heads.
However, the diameter can be increased towards the upper end 26 of
the tip section 18 to increase both torsional and bending
stiffness.
[0034] 3) For the same weight tip section 18, increasing the
diameter at the upper end 26 decreases the wall thickness and
reduces durability.
[0035] 4) To minimize the weight of the tip section 18, the wall of
the tip section 18 can be made thinner. However, as the wall
thickness is reduced, the strength and stiffness of the tip section
18 is reduced.
[0036] 5) As the diameter and wall thickness of tip section 18 is
varied, the bending stiffness (flex) is also changed. If the
bending stiffness (flex) is too high or too low the playability and
feel of the shaft becomes unacceptable.
[0037] Extensive playability and durability testing has allowed an
acceptable geometry range and a preferred geometry to be defined
for the tip section 18 of a 46 inch wood shaft weighing between 65
g and 90 g.
[0038] If the length of tip section 18 is less than 6 inches it
does not provide sufficient torsional stiffness to improve shot
accuracy. FIG. 2 shows how the torque of the club, as measured
using a torque test, is reduced as the length of the tip section is
increased. FIG. 3 shows the lower torque characteristics of a steel
tip compared to a graphite tip.
[0039] If the tip section 18 is greater than 12 inches, the shaft
weight is undesirably increased and the center of gravity position
of the shaft 16 is moved too far towards the tip end 24. FIG. 4
shows how the shaft weight increases with tip length. FIG. 4 also
shows that with shaft weights for tip lengths between 6 and 12
inches it is possible to achieve club swing weights ranging from D1
to D5 using an industry accepted head weight.
[0040] If the diameter of the upper end 26 of the tip section 18 is
increased above 0.415 inches, the bending stiffness becomes
undesirably high adversely affecting tip flexibility and providing
a low ball trajectory and a harsh feel to the club. Likewise, if
the diameter of the upper end 26 of the tip section 18 is reduced
below 0.385inches, the bending stiffness is undesirably low
providing a high ball trajectory and too soft a feel to the
club.
[0041] Durability testing carried out with an air cannon has shown
that diameters above 0.415 inches for the upper end 26 of tip
section 18 with a length range from 6 to 12 inches and an overall
weight of shaft 16 of less than 65 g does not provide a tip section
18 with sufficient durability.
[0042] In the preferred embodiment, a 46 inch wood shaft weighs 75
g and has a tip section 18 with a length of 8 inches and a diameter
at the upper end 26 of .4 inches and a diameter of 0.335 or 0.350
inches at the lower end 24. Such a preferred tip section 18 has a
torque of less than 0.6 degrees over the 8 inch length when
measured using a torque test. This compares with a torque of
greater than 1.5 degrees for the tip section of a typical graphite
shaft measured using the same test method.
[0043] Turning now to FIG. 5, the joint 30 of FIG. I is illustrated
in greater detail. An important aspect affecting the durability of
the shaft 16 is the strength of the joint 30 between the metal tip
section 18 and the composite butt section 20. As can be seen, the
tip section 18 is in the form of a hollow metal cylinder and the
butt section 20 is formed as a hollow composite cylinder. The butt
section 20 includes a reduced diameter cylindrical portion or plug
32 for insertion into the tip section 18. The reduced diameter
portion 32 may be formed during the lay-up of the composite butt
section 20 or may be formed by grinding away a pre-selected annular
amount of the butt material after initial formation. The reduced
diameter portion 32 is dimensioned to ensure a sufficient overlap
and durable interconnection with the tip section 18.
[0044] The metal tip section 18 and composite butt section 20 are
joined together with an adhesive, such as epoxy bond 31. The
thickness of the adhesive 31 is carefully controlled and the
surface area of the tip section 18 and butt section 20 along the
adhesive 31 is sufficient to ensure adequate strength. Bond
strength is selected such that the joint 30 does not fail in shear
from the torsional loads imposed through generally accepted levels
of abuse while playing the game of golf. Limiting the maximum
thickness of the adhesive 31 and increasing the surface area of the
joint 30 also maintains the highest straightness standard for the
assembled shaft 16.
[0045] Static and dynamic durability testing has shown that bond
thickness should be controlled to between 0.003" and 0.006".
Testing has also shown that for a metal tip section 18 with a
diameter at the upper end 26 of between 0.385" and 0.415" the
composite butt section 20 should be inserted into the metal tip
section 18 between about 0.75" and about 1.5" to provide an
adequate bond area. In the preferred embodiment, a 46 inch shaft
driver has a bond thickness of .0045" and the composite butt
section 20 is inserted 1.25" into the metal tip section 18. Such
geometry has been proven to provide adequate strength and
straightness in the assembled shaft 16.
[0046] The overall bending stiffness of the shaft 16, which defines
the shaft flex, is influenced by the design of the tip section 18,
the butt section 20 and the geometry of the joint 30. Local
stiffness in the joint could be high and the length of the joint 30
must be such to provide sufficient durability while not being
excessively stiff.
[0047] Flex ranges for various categories of players with different
swing characteristics are generally accepted throughout the
industry with those provided by True Temper Dynamic (trademark)
shafts often being used as a point of reference. Using the geometry
range and overall shaft weights defined above, FIG. 6 shows the
bending stiffness of shaft 16 through the joint compares favorably
to that of a Dynamic shaft ensuring excellent feel and desirable
ball flight. The stiffness of the shaft in FIG. 6 is measured as
the tip deflection in a simple cantilever load test.
[0048] FIGS. 7 and 8 compare the wall thickness along the length of
the metal tip section 18 and composite butt section 20 in the
preferred embodiment of shaft 16 with the wall thickness found in a
popular True Temper Dynamic (trademark) steel shaft and a popular
Grafalloy Prolite (trademark) graphite shaft. It will be apparent
that the wall thickness in the shaft 16 is very different to that
in the available True Temper steel and Grafalloy graphite shafts.
This illustrates that the shaft 16 cannot be made by bonding
together tip and butt sections cut from commercially available
steel and graphite shafts.
[0049] Referring again to FIG. 5, the formation of the reduced
diameter portion 32 also defines an edge in the form of a radial
wall 34 in the butt section 20. Although the radial wall 34 is
illustrated as extending orthogonally to the reduced diameter
portion 32, the radial wall 34 may also be formed at an acute or
obtuse angle relative thereto. The radial wall 34 is preferably
dimensioned so as to be equal to or slightly greater than the sum
of the thickness of the end 38 of the tip section 18 and the
thickness of the adhesive 31 so as to yield a smooth-wall,
concentric transition between the tip section 18 and the butt
section 20 along the perimeter of the shaft 16 adjacent the joint
30.
[0050] Turning now to FIG. 9, a second embodiment of the present
invention is illustrated. In this embodiment, the components which
are the same as those in the previous embodiment are identified
with the same reference numeral but increased by 200. The second
embodiment differs from the previous embodiment by the insertion of
an insulating layer 252 in the form of a plurality of spacers
between the tip section 218 and the butt section 220. The
insulating spacers 252 are preferably in the form of beads and are
preferably formed of an insulating material such as ceramic or
glass. The insulating beads 252 prevent the metal of the tip
section 218 from contacting the graphite of the butt section 220 to
reduce or eliminate galvanic corrosion within the joint 230.
[0051] The beads 252 also help control the alignment and separation
of the tip section 218 relative to the butt section 220. In this
regard, the diameter of the beads 252 is selected in accordance
with the gap 242 so as to provide sufficient space for the adhesive
231 between the beads while also coaxially aligning the tip section
218 with the butt section 220 so as to ensure a smooth perimeter
surface along the shaft 216 adjacent the joint 230. Preferably, the
beads 252 are pre-mixed with the adhesive 246 prior to its
application within the joint 230.
[0052] Turning now to FIG. 10, a third embodiment of the present
invention is illustrated. In this embodiment, the components which
are the same as those in the previous embodiments are identified
with the same reference numeral but increased by 300. The third
embodiment differs from the previous embodiments by the inclusion
of an insulating layer 352 in the form of an overlayer between the
tip section 318 and the butt section 320. The overlayer 352 is
preferably in the form of an insulating layer integrally formed
along the outboard surface of the reduced diameter portion 332 and
is preferably formed of an insulating material such as ceramic or
glass to prevent the metal of the tip section 318 from contacting
the graphite of the butt section 320 to reduce or eliminate
galvanic corrosion within the joint 330. The layer 352 also helps
control the alignment and separation of the tip section 418
relative to the butt section 320. The layer 352 is preferably
formed by forming the butt section 320 with a relatively thick
layer of glass at one end thereof prior to the formation of the
reduced diameter portion 332. The reduced diameter portion 332 is
then formed by grinding away a pre-selected annular amount of the
glass so as to leave the layer 352 as an outboard surface of the
reduced diameter portion 332. In this way, the fabric 352 isolates
the remaining composite material of the butt section 320 from the
metallic material of the tip section 318.
[0053] Referring to FIGS. 11 a and 11 b, in production shafts, a
plastic ferrule 500 is incorporated in the joint 430 between the
steel tip 418 and the graphite butt section 420. The ferrule 500,
is made from suitable extruded or injection molded plastic and is
used to accommodate any slight geometrical misalignment between the
graphite section 420 and steel section 418. The outside diameter of
the ferrule 500 is sized to be slightly larger than the diameter of
either the graphite section 410 or steel section 418. After
assembly, excess material can be removed from the plastic ferrule
500 either by buffing on a fine abrasive belt or by wiping with a
solvent such as acetone. Removing material from the ferrule 500 in
this way can provide a smooth transition on the outside surface
between the steel and graphite sections 418 and 420.
[0054] The cross section of the ferrule 500 can be altered from the
rectangular form in FIG. 11 a to incorporate inwardly sloping faces
as shown in FIG. 11 b. Such ferrule geometry can be used to
accommodate a small radius in the corner of the machined graphite
butt section 420 that can ease the manufacture of the shaft
416.
[0055] Referring again to FIGS. 1 and 2, the steps for
manufacturing the shaft 16 will be described. The hollow
cylindrical butt section 20 is formed to a given length by
arranging a plurality of layers of a pre-selected composite fibers
such as carbon-graghite at different angles relative to one another
and bonding them with a resin. The butt section 20 may be formed
with parallel, tapered or stepped sidewalls as desired. The reduced
diameter portion 32 is formed at one end of the butt section 20
during lay-up or by grinding away a pre-selected annular amount of
the material at one end thereof.
[0056] The hollow cylindrical tip section 18 is formed to a given
length by drawing a blank of metallic material such as a high
strength steel or aluminum through a mandrel. The tip section 18
may be formed with parallel, tapered or stepped sidewalls as
desired. The length and weight of the tip section 18 is selected as
described above.
[0057] An adhesive is deposited on at least one of the reduced
diameter portion 32 and the inside of the tip section 18. The
reduced diameter portion 32 is then telescopically inserted within
the tip section 18. As illustrated in FIGS. 9 and 10, an insulating
layer 52 may be inserted between the tip section 18 and the butt
section 20 to prevent galvanic corrosion within the joint 30.
[0058] The foregoing relates to preferred exemplary embodiments of
the present invention, it being understood that other embodiments
and variants thereof are possible within the scope of the
invention, the latter being defined by the appended claims.
* * * * *