Golf club shaft having selective reinforcement

A golf shaft selectively reinforced with a composite outer shell substantially shorter in length than the golf shaft. A single shell is molded at a selected location over the shaft. The location of the shell controls the kick point of the golf shaft. The shell is comprised of a reinforced polymeric composite.

The present invention relates to golf club shafts and particularly to a 
golf club shaft having a reinforced polymeric composite shell selectively 
secured to said shaft so as to reinforce the shaft, vary the kick point of 
said shaft, and dampen vibration. 
BACKGROUND OF THE INVENTION 
In recent years, golf club shafts formed of fiber reinforced plastic have 
increasingly replaced metallic shafts in order to attain weight reduction. 
Such shafts are usually manufactured by rolling layers of oriented 
unidirectional prepreg (of carbon/graphite fibers) over a metallic 
mandrel. The lay-up is then compressed and heated to cure the epoxy matrix 
and form the shaft. 
In most of the conventional fiber-reinforced plastic shafts, the fiber 
orientation angle, which is the angle formed by each layer of prepreg 
relative to the shaft axis, varies from layer to layer paired with changes 
in shaft outside diameter through the entire shaft length and addition of 
costly high modulus fibers into certain sections of the shaft, which 
provide a particular flex section or kick point on the shaft. It is found 
to be desirable to be able to adjust the kick point, or shaft flex point, 
for various clubs in order to provide the feel of the club which is 
desirable for the golfer. 
Various means have been disclosed and used for changing the kick point of 
the club of these fiber-reinforced plastic shafts. One method of 
controlling the flex zone is disclosed in U.S. Pat. No. 4,319,750 issued 
Mar. 16, 1982. In this particular patent, various laminations fabricated 
from various layers of fiber materials embedded in a suitable synthetic 
resin material are used to adjust the kick point of the shaft, and organic 
reinforcing fibers and matrix serve to dampen vibration, thus, improving 
the feel of the shaft. 
Another means of adjusting the kick point of the shaft is disclosed in U.S. 
Pat. No. 4,725,060 issued Feb. 16, 1988. This patent also relates to 
fiber-reinforced plastic shafts. In order to adjust the kick point of the 
shaft, an intermediate section is interposed between a head-side section 
and a grip-side section, with the filament-winding angle in the 
intermediate section being different from that in the head-side and 
grip-side sections so that a maximum bendability is provided at the flex 
section. 
United Kingdom Patent Application 2,053,698A, published Feb. 11, 1981, 
discloses a golf club having a metal shaft, with the shaft being 
reinforced adjacent the hosel and/or the hand grip by a bonded sheath of 
carbon fiber-reinforced thermosetting plastic material which renders the 
shaft playable. 
United Kingdom Patent Application 2,053,004, published Feb. 4, 1981, 
discloses a golf club shaft which has a portion intermediate the 
extremities of the shaft which is of increased mass per unit length. This 
controls the position of the dynamic "kick" or "flex" of the shaft. 
U.S. Pat. No. 4,135,035, issued Jan. 16, 1975, discloses the use of aramid 
and carbon to form a lightweight, stiff golf club shaft. 
Canadian Patent 705,035, issued Mar. 2, 1975, discloses a ball bat which is 
reduced in cross-section at the handle so as to provide a sleeve with a 
flush fit. 
U.S. Pat. No. 4,280,700, issued July 28, 1981, discloses a golf club set 
where the grip is enlarged to enhance holding the club. The grip includes 
a weighted insert. 
U.S. Pat. No. 3,614,101, issued Oct. 19, 1971, discloses a golf club shaft 
which uses a lightweight wrapping for the grip. 
While the above patents provide the desired results, it is quite clear that 
such systems are available only in fiber-reinforced plastic and some 
specially designed metallic shafts. These shafts cannot be used without 
reinforcement due to lack of durability and weakness of the shaft. Even 
when reinforcing the shafts, the incorporation must be done during the 
manufacture of the shaft itself. When reinforcing a particular portion of 
a metallic shaft, the wall thickness and, therefore, the weight of the 
shaft are increased. 
Accordingly, it would be desirable to be able to adjust the kick point and, 
thus, the feel of the shaft in a relatively easy-to-manufacture process 
using high strength/weight and high stiffness/weight ratio materials. The 
shaft of the present invention has good durability and stiffness even 
before the shaft is laminated with the novel composite combination shell 
described below. The use of 50% by volume aramid reinforcement is 
necessary as well as a strand angle between 30.degree. and 45.degree.. 
Further, no sandblasting is necessary since the braided reinforcement is 
bonded directly to the c steel shaft by the epoxy resin in the shell. 
Additionally, without the use of the aramid, the feel of the hit (with 
reference to vibration dampening) would be too severe using graphite 
bondings at an angle below 30.degree.. The present invention provides such 
a means for selecting the kick point of a shaft and reinforcing a section 
of the shaft by use of the lighter, stiffer composite material. 
SUMMARY OF THE INVENTION 
The present invention uses either a metallic or a reinforced plastic shaft 
which is selectively reinforced with a reinforced polymeric composite 
shell. The shell is substantially shorter in length than the golf shaft 
and may be secured to the shaft at selected locations over the shaft. The 
location of the shell controls the kick point of the golf shaft. The shell 
is formed from a sleeve of prepreg material containing epoxy resin and 
fibers. When the sleeve is placed about a section of the shaft and heated 
under pressure, a shell of a reinforced composite braided structure is 
secured in place. In the present invention, the braided reinforcement 
preferably consists mixture of aramid such as Kevlar and carbon/graphite 
fibers. When the braided reinforcement sleeve is placed over the steel 
shaft and pressure and heat are applied, the epoxy resin from the 
preimpregnated braid adheres to the chromed shaft so as to form the 
finished shell and laminate it to the shaft. The resultant composite shell 
serves to dampen vibrations, thus improving the feel of the club. The 
composite shaft of the present invention has a cost advantage over an 
expensive, high-modulus, composite shaft with the same torsional value.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown golf club 11 having shaft 13 
terminating at one end in club head 15 and at the other end in grip 19. In 
one embodiment of the invention there is shown braided composite shell 17 
which, in the illustration, extends from the butt end and outwardly from 
the grip. Preferably, composite shell 17 extends a distance L of at least 
six inches from the butt end of the club. A ferrule 18 of a material such 
as cellulose acetate-butyrate is secured about the distal end of shell 17. 
FIG. 2 is a partial sectional view of the shaft of FIG. 1, showing the 
location of composite shell 17 about shaft 13 and inside of grip 19. As 
shown, shell 17 is formed about the end of the shaft and is laminated to 
the interior wall of the shaft. For purposes of clarity, the ferrule is 
not shown. As indicated, braided composite shell 17 is located, in this 
instance, at the butt end of the club. 
The braided composite shell is comprised of reinforcement and resin matrix. 
The reinforcement can be any high-strength reinforcing fiber such as 
carbon/graphite, aramid, fiberglass, ceramic, other organic or inorganic 
fibers, etc., or combinations thereof. The matrix can be a toughened 
polymeric matrix (e.g., thermoset matrices such as epoxy or vinyl ester, 
or thermoplastic matrices such as nylon 6, 6, ABS, etc.). Preferably, the 
composite shell in its final configuration about the shaft has a thickness 
between 0.015 inch and 0.020 inch. 
After molding the composite shell to the shaft, a new flex, bounce point, 
or kick point is created to improve the feel by reducing vibration and 
playability of the shaft. This effect is obtained by increasing structural 
stiffness as well as reinforcing that particular area of the shaft where 
the composite shell is located. 
For instance, a steel shaft reinforced on the butt end as shown in FIG. 1 
would effectively improve the feel by reducing vibrations of the club. 
Further, it lowers the kick point, thus creating higher trajectories on 
the golfer's shots. This has long been known to be an area of needed 
improvement by golfers. 
Even though the additional material increases the overall weight of the 
shaft, a weight savings can be achieved with the use of a lightweight grip 
to fit over the additional material, thus creating standard or 
lighter-weight shafts, depending on what type of metallic shaft is used. 
In fact, it is critical to marry the lightweight grip to the hybrid shaft 
to keep good feel and playability for the golfer and to keep the balance 
point of the shaft proper to yield normal "swing weights" of D1-D2 on the 
14-inch fulcrum "Prorythmic" swing weight used by the majority of the golf 
industry. This marriage of the lightweight grip and hybrid shaft yields a 
lighter overall weight club at 12.25 ounces versus a standard weight club 
at 13.25 ounces. 
The preimpregnated braid (prepreg) is laminated directly to the 
vapor-degreased metal without the use of special surface preparation or 
additional adhesives other than the prepreg matrix epoxy resin impregnated 
within the reinforcing braided sleeve. 
The method of laminating the prepreg to the shaft is shown in FIGS. 6 and 
7. Sleeve 22, which includes the epoxy resin, is placed over shaft 13 and 
extended into the interior of the butt end. Removable rubber plug 20 is 
secured within the butt end so as to press the distal end of sleeve 17 
against the interior wall of the shaft. Polypropylene tape or nylon 6, 6 
film 14 is wrapped about the shaft in several layers adjacent the shell to 
prevent the resin from flowing onto the exposed section of the shaft. 
Polypropylene tape or nylon 6, 6 film 43 is then spirally overlapped with 
tight tension over the prepreg so as to apply pressure thereto. This 
provides a pressure substantial enough to ensure a high quality laminate. 
As an example, a 5/8" wide film is wound so as to have three to four 
overlays per film width. 
The shaft, wrapped as shown in FIG. 6, is passed through a 265.degree. F. 
oven 45 for approximately two hours. The heat and pressure cause the resin 
in the prepreg to bond to the shaft so as to secure the prepreg 
reinforcement to the shaft. It is preferable to apply the heat with the 
shaft hung vertically in the oven. When finished, film 43 and plug 20 are 
removed. When a grip is placed over the butt end, the finished shaft of 
FIG. 2 results. 
Referring to FIG. 3, there is shown schematically the effect of force F on 
standard golf shaft 21. The club is tested by placing the butt end in 
clamp 23. With a designated force F, kick point K1 occurs at a particular 
point on the shaft, as indicated. 
FIG. 4 illustrates schematically the same test results using club 13 as 
modified in the manner shown in FIG. 2. In this case, composite shell 17 
has been secured as shown in FIG. 1, extending to the butt end of the 
club. The force F, which is the same force exerted in the illustration of 
FIG. 3, shows that kick point K2 has been moved in the direction of the 
club head by the addition of composite shell 17. 
FIG. 5 is a modification which reduces the weight of the club to compensate 
for the weight of the composite shell. In this case, diameter D of section 
29 of shaft 27 has been reduced substantially a distance equivalent to the 
width of composite shell 31, which results in a diameter D of 
substantially 0.500 inch. This not only compensates for the weight, but 
also provides a smooth, continuous surface over the shaft itself. 
FIG. 8 illustrates the placement of composite web 37 further down the shaft 
adjacent the club head. A test of the forces on such a shaft is shown 
schematically in FIG. 9, wherein the placement of web 37 as illustrated in 
FIG. 7 causes kick point K3 to move in a direction towards the butt end of 
the shaft. 
As discussed above, the present invention provides a relatively economical 
and weight-saving method in which steel or other metallic shafts may be 
modified so as to adjust the kick point of the shaft. The reinforcing 
fibers, preferably at an angle between 30.degree. and 45.degree. from the 
axis of the shaft, and epoxy resin serve to dampen vibration, thus 
improving the feel of the golf club. For example, using a tailored shell 
composed of a toughened epoxy matrix stiffened with fifty per cent (50%) 
by volume aramid reinforcing fiber (e.g., Kevlar) and fifty per cent (50%) 
by volume carbon/graphite braided reinforcing strands provides both 
structural stiffness and vibration dampening since aramid fiber composites 
have an order of magnitude higher damping ratio than carbon/graphite 
reinforced composites. The strands are at an angle, FIG. 2 between 
30.degree. and 45.degree. relative to the longitudinal axis of the shaft. 
EXAMPLE 
Tests conducted by a robotic golfer developed the following results: 
Using golf heads of exactly the same loft, lie, face angle, roll and bulge, 
two identical length clubs were built to the same swing weight 
specification. The control club used was a standard steel-shafted club. 
The other club used was the shafted club of the present invention as shown 
in FIG. 1 with a shell having a composition as described above. The most 
notable difference in the clubs was the use of the shaft of the present 
invention for one club, which yielded a lighter overall weight of that 
club. This resulted from the use of a thinner grip and lighter weight 
steel shaft. 
Using a mechanical golfer and the same standard launch conditions, machine 
power, and standard test golf balls, a test was conducted where a series 
of hits were conducted with the shafted club of the present invention and 
the standard steel control club. The hits were in a face scan sequence 
where a center hit is performed, then a toe hit, center hit again, then a 
heel hit, and so on, to create a series of impact points on the test field 
that show where the golf balls would land if hit on center or off center. 
The off center hits are important to simulate the tendencies of actual 
live golfers. The test produced the following results: 
______________________________________ 
Average 
Lateral Deviation 
Distance 
from Center Line 
(Yards) 
(Yards) 
______________________________________ 
Control Club with 
Standard Steel Shaft 
Center Hit 252 1 Left 
Toe Hit 239 19 Right 
Heel Hit 249 2 Left 
Shafted 
Club of the 
Present Invention 
Center Hit 254 1 Right 
Toe Hit 247 12 Right 
Heel Hit 251 0 
______________________________________ 
If a shot pattern "spread" is created by looking at the average lateral 
deviation of the shots farthest to the left and the distance to average 
lateral deviations of the shots farthest to the right, it is seen that a 
"spread" for the control club is 21 yards while the spread for the shafted 
club of the present invention is only 12 yards. 
Referring to FIGS. 9 and 10, there is shown computer generated elipses on 
the test field showing the landing locations from the data that was 
gathered. 
As can be seen by the above information and the test field pictures of 
FIGS. 9 and 10, the shaft of the present invention was substantially more 
accurate, as well as longer in distance, most notably on the toe hits. 
The benefits of the shaft of the present invention when the shell is placed 
at the butt end of the shaft are as follows: 
(1) Stiffens the butt so as to remove unnecessary flex in the butt of the 
shaft, thus creating a slightly lower flex point for better feel and 
higher trajectory. 
(2) Achieves the same low torque (e.g. 2-2.75 degrees per 1 
ft..multidot.lb. applied torque over full shaft length) as steel shafts 
for a much lower price than a high modulus graphite composite shaft. 
(3) Allows the use of a softer flex (i.e., lighter) steel shaft that will 
create the desired stiffer flex after attaching the low density composite 
material. 
(4) Using a standard butt size of 0.560 inch to 0.635 inch and then molding 
the composite shell thereon creates a larger outside diameter of shaft 
"butt" of 0.640 inch to 0.655 inch, thus allowing the use of a lighter, 
thinner grip to yield standard outside diameter grip sizes. This allows 
the steel shaft, composite material, and light weight grip to be equal to 
the weight of a high modulus, low torque, expensive graphite shaft and 
standard grip. 
It should be noted that the non-reinforced shaft weight (prior to molding 
on the composite shell) should be greater than 90 grams to ensure a 
durable shaft base having a proper shaft flex desired by golfers. Anything 
less than this weight, such as shown in the above-referenced U.K. Patent 
Application 2,053,698A, would have durability problems and very weak flex 
characteristics. 
While a standard grip could be used over the composite shell and still 
retain the benefits of the shell as discussed above, the reduction of 
weight by using a lighter grip is a definite advantage and, as stated 
earlier, critical to keeping the good feel and playability for the golfer. 
The weight of the composite material is from 10 to 15 grams per foot and 
preferably 13 grams per foot. The length of the material will determine 
the final weight of the shell. 
The weight of the grip is preferably from 20 grams to 39 grams. This is 
substantially lighter than the weight of the standard grip, which is 
approximately 52 grams. 
______________________________________ 
EXAMPLE OF WEIGHTS 
Weight 
in Grams 
______________________________________ 
Shaft of the Present Invention 
Light Weight Steel Shaft 
97 
Composite Material 13 
Light Weight Grip 39 
149 
Expensive Graphite Shaft 
High Modulus Graphite Shaft 
98 
Standard Grip 52 
150 
______________________________________ 
The above description and drawings are illustrative, only, since 
modifications could be made without departing from the invention, the 
scope of which is to be limited only by the following claims.