Lightweight shaft

A lightweight shaft 22 of generally tubular configuration, for use with a golf club 20, is formed with a first layer 34 of a non-metallic composite material of a given density including graphite fibers 86 and cured epoxy resin 86. A second layer 38 of the shaft 22 is composed of a two foam half-forms 124, or a foam full-form 142, having a density which is lower than the given density and which are located around at least a portion of the length of the first layer 34. A third layer 40 of the shaft 22 is also composed of a non-metallic composite material including graphite fibers 86 and cured epoxy resin 86 which is located around the second layer 38 of the shaft 22. A portion of the third layer 38 is also located about the first layer 34 at a tip end 30 of the shaft 22.

BACKGROUND OF THE INVENTION 
This invention relates to a lightweight shaft and particularly to a 
lightweight shaft which forms a portion of a golf club. 
Golf clubs typically include a club head secured to a tip end of a club 
shaft and a hand grip assembled at a butt end of the shaft. The butt end 
of the shaft is formed with a diameter which is larger than the diameter 
of the tip end. The portion of the shaft which extends between the butt 
end and the tip end thereof is usually tapered from the larger diameter at 
the butt end to the smaller diameter of the tip end. The butt end and the 
tip end of the shaft could also be tapered or straight with a uniform 
diameter as noted above. 
In playing the game of golf, a golfer swings the club and aims the head 
thereof toward a golf ball which is located, for example, on a ground 
level surface. Ideally, when the club head strikes the ball, the ball is 
directed in a long trajectory toward, and on line with, an associated 
hole-like cup located on a fine grass surface. 
Many years ago, shafts for golf clubs were made from wood such as, for 
example, hickory which was suitable for the bending and twisting to which 
the club was subjected when swung by the golfer. However, the use of wood 
for the shafts influenced the manner in which the golfer had to swing the 
club. Later, clubs with metal shafts, such as steel shafts, were developed 
and evolved into a highly successful product which enhanced the golfers 
playing of the game. In recent years, clubs with non-metallic shafts have 
been developed and provide a viable and popular option to the use of the 
metal shafts. The non-metallic shafts are typically made from a fiber 
reinforced polymer matrix composite such as, for example, graphite fiber 
and an epoxy matrix. 
There are several factors which are considered when designing a golf club 
to enhance the playing of the game. Perhaps the most important factor is 
the weight of the shaft. One of the parameters which is considered in the 
use of a golf club is the "swing weight" of the club. The swing weight 
parameter represents generally the weight of the club as it is being swung 
and is related to the overall weight and the weight distribution in the 
club. Clubs are classified in several principal grades, and several sub 
grades within each principal grade, based on the swing weight of the 
clubs. The clubs with a low swing weight are typically used by the weaker 
hitters while the higher swing-weight clubs are used by the stronger 
hitters. 
The development of the composite shaft resulted in a shaft which is lighter 
in weight than the steel shaft and thereby presented a weight enhancement, 
particularly for the weaker hitters who use the low swing-weight clubs. 
When the composite shaft was developed, it provided an option for some 
golfers to switch from a club with the heavier metal shaft to a club with 
the lighter composite shaft if the golfer experienced improved play with 
the lighter club. Also, with the lighter composite club, the weight of the 
club head could be increased slightly whereby the speed of the head is 
increased which translates into increases in ball speed and distance 
thereby further enhancing the golfers playing of the game. 
With the realization and recognition that the above-noted advantages can be 
attained by using the lighter composite clubs, there is a need to develop 
even lighter clubs to provide further enhancement of the playing of the 
game by golfers. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of this invention to provide a lightweight 
shaft. 
Another object is to provide a lightweight shaft for use as a component of 
a golf club to enhance the feel and playability of the club. 
A further object of this invention is to provide a lightweight shaft which 
can be used to form a component of any type of golf club such as woods, 
irons, wedges or putters. 
Still another object of this invention is to provide a low cost composite 
shaft for use as a lightweight component of a golf club. 
With these and other objects in mind, this invention contemplates a 
lightweight shaft which includes a first layer of a material of a given 
density, a second layer of a material of a density lower than the given 
density and in engagement with at lease a portion of the first layer, and 
a third layer of a material of a density greater than the density of the 
second-layer material and in engagement with at least a portion of the 
second layer. 
This invention further contemplates a method of making a lightweight shaft 
which includes the steps of forming a first layer of a first material of a 
given density in a generally tubular configuration, placing a second layer 
of a second material having a density lower than the given density over at 
least portions of the first layer, and forming a third layer of a third 
material having a density greater than the density of the first layer over 
at least portions of the second layer. 
Other objects, features and advantages of the present invention will become 
more fully apparent from the following detailed description of the 
preferred embodiment, the appended claims and the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, a golf club 20 is formed by a shaft 22, a club head 
24, shown in phantom, and a grip 26, also shown in phantom. The shaft 22, 
which is generally tubular with an axial opening 27 (FIG. 2), is formed 
with a butt end 28 to which the grip 26 is attached and is also formed 
with a tip end 30 to which the head 24 is secured. An intermediate section 
32 of the shaft 22 extends between the butt end 28 and the tip end 30 
thereof and tapers inwardly from an inboard extremity of the butt end to 
an inboard extremity of the tip end. The butt end 28 and the tip end 30 
each could be of a uniform diameter, or either or both of the butt and tip 
ends could be tapered or the entire shaft 22 could be tapered from one 
extremity to the other, all without departing from the spirit and scope of 
the invention. 
As shown in FIG. 2, the shaft 22 of the preferred embodiment is formed by a 
first layer or skin 34 which forms an inner layer of the shaft, the inner 
wall of which forms the axial opening 27. The layer 34, which has a given 
density, is composed of a composite material such as graphite fibers 86 
(FIG. 6) and an epoxy resin matrix 88 (FIG. 6) as described hereinbelow. 
The fibers of the composite material also could be fiberglass, aramid, 
boron or other suitable fiber materials, and the epoxy resin matrix could 
be polyester, vinylester, nylon or any other suitable thermoset or 
thermoplastic matrix, all without departing from the spirit and scope of 
the invention. The fibers 86 are typically in a parallel, spaced array 
within the epoxy resin 88 and are arranged in the formation of the shaft 
22 so that the fibers are parallel with, and/or on a bias with respect to, 
an axis 36 of the shaft. 
The shaft 22 is further formed by a second layer or core 38 of a low 
density foam material. The foam material used in the preferred embodiment 
to form the second layer 38 is available commercially under the trademark 
"ROHASELL" from Richmond Aircraft Products of Norwalk, Calif., and is 
manufactured by Rohm Gmbh of Darmstadt, Germany. The foam material of the 
second layer 38 has a density much lower than the given density of the 
first layer 34. Other suitable foam materials and low density materials 
could be used to form the second layer 38 without departing from the 
spirit and scope of the invention. 
The shaft 22 is also formed with a third layer or skin 40 which forms an 
outer layer of the shaft. In the preferred embodiment, the third layer 40 
is composed of the same composite material as the first layer 34 and is 
arranged so that the fibers thereof are parallel and/or on a bias with the 
axis 36 of the shaft 22. 
As further illustrated in FIG. 2, the preferred embodiment of the shaft 22 
is in a laminated configuration from the outboard extremity of the butt 
end 28 to a location generally at the inboard end of the tip end 30 and 
includes the first or inner layer 34, the second or core layer 38 and the 
third or outer layer 40. The remaining portion of the shaft 22, which is 
generally defined by the tip end, is formed by a lamination of the first 
layer 34 and the third layer 40. The portion of the second layer 38, which 
is located in the butt end 28 of the shaft 22, is generally of a uniform 
diameter. The remaining portion of the second layer 38 decreases in 
thickness toward the tip end 30 and along the intermediate section 32. 
A second embodiment of the invention is shown in FIG. 3 in the form of a 
shaft 42. Shaft 42 is formed by a first or inner layer 44 in the same 
manner, and is composed of the same composite material, as the first layer 
34 of the shaft 22. The shaft 42 is formed with a second layer or core 46 
in a butt end 48 of the shaft. The second layer 46 is composed of the same 
low density foam material as the second layer 38 of the shaft 22 (FIG. 2). 
A third or outer layer 52 of the shaft 42 is composed of the same 
composite material as the first layer 44 thereof and overlays the second 
layer 46 generally in the butt end 48 and blends with the first layer 
generally along an intermediate section 50 and at a tip end 54 of the 
shaft. 
As shown in FIG. 4, a third embodiment of the invention includes a shaft 56 
having a first or inner layer 58 formed in the same manner, and composed 
of the same composite material, as the first layer 34 of the shaft 22. A 
second layer or core 60 of the shaft 56 is formed by a low density foam 
material, which is the same as the foam material of the shaft 22, and is 
located over the first layer 58 generally along an intermediate section 62 
of the shaft 56. A third or outer layer 64 of the shaft 56, of the same 
composite material as the third layer 52 of the shaft 42, is in engagement 
with the first layer 58 at a butt end 66, with the second layer 60 of the 
foam material along the intermediate section 62 and with the first layer 
58 along a tip end 68 of the shaft 56. 
Referring to FIG. 5, a shaft 70 illustrates a fourth embodiment of the 
invention and includes a first or inner layer 72 formed in the same 
manner, and composed of the same composite material, as the first layer 34 
of the shaft 22. A second layer or core 74 of the shaft 70 is composed of 
the same low density foam material as the second layer 38 of the shaft 22. 
The second layer 74 is located at a tip end 76 of the shaft 70 and extends 
from the outboard extremity of the tip end to a juncture of the tip end 
with an intermediate section 78 of the shaft. A third or outer layer 80 of 
the shaft 70, which is composed of the same composite material as the 
first layer 72 of the shaft, is in engagement with the second layer 74 at 
the tip end 76 of the shaft and is in engagement with the first layer 72 
along the intermediate section 78 and a butt end 82. 
In general, each of the first and third layers of the above-described 
shafts 22, 42, 56 and 70 may be formed by several uncured layers of the 
composite material which blend together when heated and cured to form, 
respectively, the first and third layers without departing from the spirit 
and scope of the invention. 
Each of the above-described shafts 22, 42, 56 and 70 may be used for any 
type of golf clubs including woods, irons, wedges and putters. The 
above-described structure of these shafts allows for the increased 
stiffness of a sandwich or laminated configuration which decreases the 
requirements of a thick wall section in comparison with a conventionally 
designed golf shaft. The design of each of these above-described shafts 
separates a single load carrying member, such as an all-composite-material 
shaft typically found in a conventional shaft, into two thinner walls 
formed by the above-described first and third layers of the composite 
material. The foam layer or core, represented by the above-described 
second layers, is sandwiched between the two thinner walls in each of the 
above-described embodiments. This allows for a much stiffer and stronger 
structure with the same mass of wall material when compared with the 
conventional all-composite-material shaft. Taking this into consideration, 
the wall mass may be reduced to obtain a shaft stiffness consistent with 
the stiffness of the conventional all-composite-material shaft and thereby 
reduce the overall weight of the shafts of each of the above-described 
embodiments. A shaft embodying the above-described inventive structures 
also produces greater feel and response to the golfer who uses a club 
which includes the shaft. 
While the preferred embodiment, and the second, third and fourth 
embodiments are formed by first and third layers of the composite material 
as described, the first and/or third layers may also be composed of 
suitable metals such as, but not limited to, aluminum, steel or titanium 
without departing from the spirit and scope of the invention. 
The material which forms the second layer in each of the above-described 
shafts 22, 42, 56 and 70 must have sufficient compressive strength to 
transmit compressive loads from the outer or third layer to the inner or 
first layer. This will improve the overall stiffness and buckling strength 
of the inventive shafts. Also, while the four above-described embodiments 
of the inventive shafts 22, 42, 56 and 70 define particular locations of 
the foam material, the foam material could be placed at locations other 
than those described above without departing from the spirit and scope of 
the invention. For example, the foam layer could be located between the 
first and third layers along the entire length of the shaft. Or separate 
sections of the foam material could be located in spaced portions, but not 
all, of any one major section of the shaft (i.e., the butt end, the 
intermediate section or the tip end) or in any combination of two or three 
of the major sections of the shaft. 
As shown in FIG. 19, a shaft 160 represents variations of a fifth 
embodiment of the shaft and is composed of a first layer or skin 162 and a 
second layer of skin 164 in an interfacing engagement in the manner 
described above. Three separate foam layers 166, 168 and 170 are arranged 
along the axis of the shaft 160. As noted above, without departing from 
the spirit and scope of the invention, the shaft 160 could include only 
one of the three layers 166, 168 and 170, or could include any combination 
of two or three of the foam layers in the major sections of the shaft as 
illustrated. 
While the wall mass of the inventive shafts 22, 42, 56, 70, and 160 is 
thinner than the conventional all-composite-material shaft, the inventive 
shafts are formed with a conventional outside dimension planform with the 
major thickness differences appearing within the laminated structure. 
The following chart shows dimensions of the preferred embodiment of the 
invention which correlate to the dimension letters "A" "B" "C" "L" and "T" 
shown in FIG. 2. 
______________________________________ 
Dimension 
Description Woods Irons 
______________________________________ 
A Tip Diameter 0.335 in. 0.370 in. 
B Butt Diameter 
0.600 in. 0.600 in. 
C Foam End Point 
5.00 in. 5.00 in. 
L Shaft length 45.00 in. 40.00 in. 
T Foam Thickness 
2 to 3 mm. 2 to 3 
mm. 
______________________________________ 
Other dimensions could be used without departing from the spirit and scope 
of the invention. 
As noted above, several of the figures include portions which are shown 
disproportionately enlarged for illustration purposes. The dimensions of 
the chart above will provide representative dimensions for the shafts 
described herein. 
Referring to FIG. 6, in the preferred method of making the preferred 
embodiment of the invention, that is the shaft 22, a sheet 84 (one shown) 
of the composite material includes the graphite fibers 86 held and 
suspended in a parallel, spaced array by the uncured epoxy resin 88. It is 
to be understood that the fibers 86 could be arranged in a different 
parallel array or matrix other than the array illustrated in FIG. 6 
without departing from the spirit and scope of the invention. Also, the 
illustrated configuration of the sheet 84 is representative of a 
configuration of such a sheet. Several different configurations of the 
sheet 84 could be used, depending on the desired configuration of the 
cured first layer 34. As shown in FIG. 7, a first of the composite sheets 
84 is wrapped around a mandrel 90. The mandrel 90 is formed (1) with a 
butt end 89 of uniform diameter along a given length thereof, (2) with a 
tip end 91 for a given length of the shaft at a uniform diameter smaller 
than the uniform diameter of the butt end, and (3) with a tapered 
intermediate section 93 extending between inboard extremities of the butt 
and tip ends. The mandrel 90 is typically formed from a metal such as, for 
example, steel but could be formed from any other suitable metal or 
non-metal material without departing from the spirit and scope of the 
invention. The sheet 84 could be wrapped around the mandrel 90 in such a 
manner that the fibers 86 are parallel, and/or on a bias, with an axis 98 
of the mandrel. 
As noted above, if desired, several uncured sheets 84 could be wrapped 
around the mandrel 90 to form the first layer of any of the shafts 22, 42, 
56 and 70 to obtain a desired thickness and/or fiber orientation of the 
first layer without departing from the spirit and scope of the invention. 
Thereafter, the foam layer such as, for example, the second layer or core 
38 of the shaft 22, is to be prepared for assembly about the first layer 
34. Referring to FIG. 8, the preferred technique for preparing the second 
or foam layer 38 involves the step of feathering a sheet 102 of the 
above-noted foam material from an intermediate portion 104 to an edge 106 
thereof to form a section 108 of uniform thickness and a section 110 of 
varying thickness. Thereafter, a major flat surface 112 of the feathered 
sheet 102 is placed on a mold section 113 (FIGS. 9 and 10) having a cavity 
114 formed therein so that the sheet covers the cavity. The cavity 114 is 
formed with a cylindrical section 116 at one end thereof and a concave 
section 118 extending from an inboard end of the cylindrical section to an 
opposite end 119 of the cavity which is in line (FIG. 9) with an edge 121 
of the mold section 113 and which tapers outward from the inboard end to 
the opposite end. As shown in FIG. 11, another mold section 120, having a 
forming section 122 in a configuration complementary to the configuration 
of the cavity 114, is assembled with the mold section 113 so that the foam 
sheet 84 is captured between the cavity and the forming section. 
Thereafter, the mold sections 113 and 120 are heated so that the foam 
sheet 84 assumes the shape illustrated in FIG. 12 as a foam half-form 124 
having a cylindrical section 126 of uniform thickness, an inward tapered 
section 128 of decreasing thickness from its juncture with the cylindrical 
section to the opposite end thereof and a pair of spaced mating surfaces 
129 which are in the same plane. 
In another technique for making the second or core layer 38, and referring 
to FIG. 13, a mold 130 is formed with a cavity 132 which includes a 
cylindrical section 134 and an inward tapered, cone-like section 136. A 
cavity insert 138, which has an outer configuration which is complementary 
to the configuration of the cavity 132, is moved into the cavity to form a 
cavity space 140 between the cavity and the insert. A foam material in a 
liquid form is poured into the cavity space 140 and the mold 130 is heated 
and cooled to cure the foam in the configuration of the cavity space 140. 
The cavity insert 138 with the formed foam is retracted from the mold 130 
to reveal a foam full-form 142, as illustrated in FIG. 14, which is 
removed from the insert. The full-form 142 is formed with an axial opening 
144 which extends through the full-form an includes a cylindrical section 
146 of uniform diameter and an inward tapered section 148 of varying 
thickness. If the full-form 142 were cut in half vertically through the 
centerline, each of the two halves formed thereby would appear essentially 
as the half-form 124 of FIG. 12. An example of a fluid foam material which 
can be used for this process is a phenolic foam commercially available 
under the trademark "THERMO-COR2" from American Foam Technologies of 
Ronceverte, W.V. 
If the technique involving the half-form 124 is used, two of the half-forms 
are positioned around the sheets 84 which are wrapped on the mandrel 90, 
as shown in FIG. 15, with the mating surfaces 129 of the two half-forms 
being in abutting engagement. The two half-forms 124 are retained in this 
assembly by use of a small strip of adhesive tape (not shown) or by 
applying a small amount of glue to the abutting surfaces 129 of the two 
half-forms. 
If the technique involving the full-form 142 is used, a single full-form is 
assembled axially over the mandrel 90 and the sheets 84 wrapped around the 
mandrel to encompass the wrapped sheets in a manner similar to sectional 
illustration of FIG. 15. 
In either of the above-described techniques, a portion 150 of the wrapped 
sheets 84 of the first layer 34, which is adjacent to the tip end 91 of 
the mandrel 90, will not be covered by the half-form 124 or the full-form 
142 as shown in FIGS. 15 and 16. 
Thereafter, as shown in FIG. 17, a second one, or several if desired, of 
the sheets of the composite material, which is designated by the numeral 
"84a" to distinguish from the first-layer sheets 84, is wrapped around the 
half-forms 124, or full-forms 142, and the exposed portion 150 of the 
first wrapped sheets 84. As shown in FIG. 18, a heat-shrinkable film 152 
is positioned to be, and is eventually, placed over the third wrapped 
sheet or sheets 84a. The assembly of the mandrel 90, the sheets 84 and 
84a, and the half-forms 124 or the full form 142 is then processed through 
an oven (not shown). While in the oven, the epoxy resin 88 of the wrapped 
sheets 84 and 84a is transformed into a fluid state and the film 152 
shrinks to compress the fluid epoxy resin with the fibers 86 remaining in 
place. The film 152 shrinks generally to the shape defined by butt end 89, 
intermediate section 93 and the tip end 91 of the mandrel 90. The assembly 
of the mandrel 90, the sheets 84 and 84a and the shrinkable film 152 is 
then removed from the oven and the epoxy resin 88 is allowed to cure 
generally in the shape defined by the shrunken film and the mandrel. The 
film 152 is removed to reveal generally the shaft 22 as illustrated in 
FIG. 2. During the heating process, the epoxy resin 88 blends generally 
into an homogenous form on each side of the forms 124 or 142, and at the 
portions adjacent the tip end 91 of the mandrel 90, with the fibers 86 
remaining in place. In addition, the portions of the composite sheets 84 
and 84a which are in engagement with the forms 124 or 142 blend to some 
extent with the adjacent portions of the foam forms to enhance the 
unitized formation of the sheets with the foam forms. However, the 
interior portions of the half-forms 124 or the full-form 142 retain their 
structural integrity with respect to the foam material thereof. After the 
curing process has been completed, the shrunken film 152 is removed to 
reveal the shaft 22 mounted on the mandrel 90. 
It is noted that, except for the portions of the above-described heating 
and curing process which relate to the foam half-form 124 and the 
full-form 142, the heating and curing process is similar to conventional 
processes for making composite shafts. 
The mandrel 90 can be removed from assembly with the cured first, second 
and third layers 34, 38 and 40, respectively, of the shaft 22 whereafter 
the third layer can be further processed if necessary or desired, to 
provide a desired sizing and/or finish on the outer surface of the shaft 
22. 
Other techniques for making the shaft 22 may be used without departing from 
the spirit and scope of the invention. For example, an autoclave technique 
can be used wherein the sheets 84 and 84a of composite material are 
wrapped around the mandrel 90 and forms 124 or 142 to form an assembly in 
the manner described above. Thereafter, a small diaphragm bag (not shown) 
is placed over the assembly and cured in an autoclave (not shown) with an 
external pressure of up to 150 psi applied to the assembly. The assembly 
is then removed from the autoclave and the bag is removed to reveal the 
completed shaft 22. 
The shaft 22 may also be made by using a pressure molding process. For 
example, a small diaphragm bag (not shown) is placed over the assembly of 
the mandrel 90, the composite sheets 84 and 84a, and the foam forms 124 or 
142 which is processed and cured in a clamshell mold (not shown) with an 
internal pressure of up to 150 psi applied to the assembly. The cured 
product is removed from the mold and the bag to reveal the completed shaft 
22 mounted on the mandrel 90. 
In general, the above-identified embodiments are not to be construed as 
limiting the breadth of the present invention. Modifications, and other 
alternative constructions, will be apparent which are within the spirit 
and scope of the invention as defined in the appended claims.