Abstract:
A club shaft for a golf club and method for making a club shaft for a golf club are provided herein. The club shaft includes a shaft butt section, a shaft tip section and a shaft intermediate section which connects the shaft butt section to the shaft tip section. The shaft intermediate section includes a shaft outer diameter which tapers from the shaft butt section to the shaft tip section. Uniquely, the amount of taper varies along the shaft intermediate section to avoid any abrupt transitions in the club shaft. The resulting club shaft has a continuous, smooth geometry, without stress concentration areas. This improves the strength, fatigue and fracture toughness of the club shaft. Further, the amount of taper can be specifically tailored to obtain a club shaft having the desired moment of inertia, resistance to torsion, mass distribution, flexure, frequency, strength, and stiffness properties.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to club shafts for golf clubs. More specifically, the present invention is directed to a golf club shaft having improved strength, stiffness, durability and torque characteristics. 
     BACKGROUND 
     The game of golf is becoming increasingly popular in the United States and internationally. Presently, golfers, both professional and non-professional, are continuously striving to improve their golf game. It is well known that the physical characteristics of the club shaft of a golf club can effect the travel of the golf ball. Club shafts having a high stiffness to weight ratio, low shaft vibration, good strength, good resistance to torsion and good resilience to fatigue are usually preferred by golfers. 
     Typically, each golf club shaft includes a shaft tip section, a shaft intermediate section and a shaft butt section. The shaft tip section typically has a relatively small outer diameter when compared to the shaft butt section. A head is secured to the shaft tip section, while a grip is secured to the shaft butt section. The shaft intermediate section extends between and tapers from the shaft butt section to the shaft tip section. Usually, the taper is substantially linear or includes a series of sequentially smaller, annular steps. 
     Unfortunately, existing club shafts are not entirely satisfactory. For example, existing club shafts can be too weak, have poor resistance to torsion and poor resilience to fatigue. One way to improve the strength and resistance to torsion of the club shaft is to increase the wall thickness of the club shaft. However, the resulting thicker walled club shaft is often too heavy and/or has other undesirable performance characteristics. 
     In light of the above, it is an object of the present invention to provide a club shaft and method for manufacturing a club shaft having improved strength and resistance to fatigue crack propagation. Yet another object of the present invention is to provide a composite club shaft having improved durability, torque characteristics and performance characteristics. 
     SUMMARY 
     The present invention is directed to a club shaft for a golf club which satisfies these needs. The club shaft includes a shaft butt section, a shaft tip section, and a shaft intermediate section which connects the shaft butt section to the shaft tip section. The shaft intermediate section has an outer diameter which tapers from the shaft butt section to the shaft tip section. 
     Uniquely, the rate or amount of taper in the outer diameter of the shaft intermediate section varies along the shaft intermediate section. Stated another way, the slope of the taper varies along the shaft intermediate section. Preferably, the outer diameter of the shaft intermediate section has a slope of approximately zero degrees relative to a shaft longitudinal axis near the shaft butt section and the shaft tip section. This allows the club shaft to have a continuous, smooth geometry and eliminates the abrupt transitions between shaft butt section, the shaft intermediate section, and the shaft tip section. The resulting club shaft has improved strength, durability and torque characteristics, without increasing the wall thickness or fiber modulus of the club shaft. 
     Each club shaft provided herein can be made by wrapping one or more patterns around a form, i.e. a mandrel or a bladder. Alternately, each club shaft could be made by winding one or more filaments around the form, or molding each club shaft in a closed die. 
     The invention is also a method for manufacturing a club shaft. The method includes the steps of: (i) providing a form; (ii) providing at least one pattern; and (iii) wrapping the at least one pattern around the form. Each of the forms can be a mandrel having an elongated cylindrical rod-like structure. Each form includes a form butt section, a form tip section, and a form intermediate section. In order to make the club shaft outlined above, the form intermediate section includes an outer diameter which tapers from the form butt section to the form tip section. Importantly, the rate or amount of taper of the outer diameter varies along the form intermediate section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
     FIG. 1 is a side plan view of a representative set of golf clubs having features of the present invention; 
     FIG. 2 is a graph which illustrates the dimensions of a first embodiment of a club shaft having features of the present invention; 
     FIG. 3 is a graph which illustrates the dimensions of another embodiment of a club shaft having features of the present invention; 
     FIG. 4 is a graph which illustrates the dimensions of yet another embodiment of a club shaft having features of the present invention; 
     FIG. 5 is a graph which illustrates the dimensions of a form having features of the present invention; 
     FIG. 6 is a graph which illustrates the dimensions of another embodiment of a form; 
     FIG. 7 is a graph which illustrates the dimensions of yet another embodiment of a form; 
     FIG. 8 is a side plan view of a plurality of patterns having features of the present invention; 
     FIG. 9 is a side plan view of a portion of a filament; and 
     FIG. 10 is a side plan view of a die which can be used to make a club shaft having features of the present invention. 
    
    
     DESCRIPTION 
     FIG. 1 illustrates a plurality of golf clubs  10  in a set  12  of golf clubs  10 . Each golf club  10  includes a head  14 , a grip  16  and a club shaft  18 . Importantly, the club shaft  18  for each golf club is uniquely manufactured and designed to have improved strength characteristics, smoother load distribution, torque characteristics and durability. This allows a golf player (not shown) to have better control over flight, trajectory, distance and shot dispersion. 
     A typical set  12  of golf clubs  10  includes a set of irons  20 , a set of woods  22 , one or more wedges  21 , and one or more putters  23 . The actual number of golf clubs  10  in a set  12  of golf clubs can vary. For example, typically, a player in a tournament utilizes a set  12  of golf clubs  10  which includes No.  1  through No.  9  irons  10  and a No.  1 , No.  3 , and No.  5  woods  22 . The irons  20 , wedges  21 , woods  22 , and putter  23  shown in FIG. 1 are for exemplary purposes. 
     FIGS. 2-4 each illustrate an alternate, cross-sectional view of a club shaft  18  positioned on a graph. It should be recognized that these embodiments provided below are merely exemplary and can be varied. Each club shaft  18  is substantially tubular and includes a shaft butt section  24 , a shaft intermediate section  26 , and a shaft tip section  28 . The grip  16  (illustrated in FIG. 1) encircles and attaches to the shaft butt section  24  while the head  14  (illustrated in FIG. 1) attaches to the shaft tip section  28 . The club shaft  18  has a shaft outer diameter  30 , a shaft inner diameter  32 , a shaft length  33  and a shaft longitudinal axis  34 . 
     Depending upon the design of the grip  16  and the head  14 , the shaft butt section  24  and the shaft tip section  28  can have a substantially constant outer diameter as illustrated in FIGS. 2-4 or a tapering diameter (not shown). The club shafts  18  illustrated herein have a shaft wall thickness  36  which varies along the shaft length  33  of the club shaft  18 . 
     The shaft intermediate section  26  connects the shaft butt section  24  to the shaft tip section  28 . Importantly, the present invention recognizes that the physical characteristics of each club shaft  18  can be tailored by adjusting the shape of the shaft intermediate section  26 . The club shafts  18  provided herein are superior to prior art club shafts because of the unique shape of the shaft intermediate section  26 . To highlight the unique shape, dashed lines designated  37 P in FIGS. 2-4 illustrates how the shaft outer diameter  30  would appear if the shaft intermediate section  26  had a substantially linear taper. Similarly, dashed lines  39 P illustrate how the shaft inner diameter  32  would appear if the shaft intermediate section  26  had a substantially linear taper. 
     It should be noted from FIGS. 2-4 that the shaft outer diameter  30  and the shaft inner diameter  32  of the shaft intermediate section  26  tapers from the shaft butt section  24  to the shaft tip section  28 . Importantly, the rate or amount of taper of the shaft outer diameter  30  varies along the entire shaft intermediate section  26 . Thus, the slope or pitch of the taper relative to the shaft longitudinal axis  34  varies along the shaft intermediate section  26 . Further, the slope of the taper of the shaft intermediate section  26  relative to the shaft tip section  28  or the shaft butt section  24 , near the shaft tip section  28  and the shaft butt section  24  is approximately zero. This allows the club shaft  18  to have a smooth, continuous shape and eliminates the abrupt transition from (i) the shaft butt section  24  to the shaft intermediate section  26  and (ii) the shaft intermediate section  26  to the shaft tip section  28 . Thus, the transition between the shaft butt section  24  and the shaft intermediate section  26  and the transition between the shaft intermediate section  26  and the shaft tip section  28  is gradual and rounded. 
     Stated another way, the shaft outer diameter  30  and the shaft inner diameter  32  of the shaft intermediate section  26  includes a superficially segmented, undulating or curved surface profile. FIGS. 2-4 illustrate three preferred embodiments of the club shaft  18 . In the embodiment illustrated in FIG. 2, the cross-sectional profile of the shaft outer diameter  30  relative to dashed lines  37 P is substantially similar to a single, rounded, sine shaped wave. Similarly, in FIG. 2, the cross-sectional profile of the shaft inner diameter  32  relative to dashed lines  39 P is also substantially similar to a ingle, rounded sine wave. Alternately, in the embodiment illustrated in FIG. 3, the cross-sectional profile of the shaft outer diameter  30  relative to dashed lines  37 P is substantially similar to a pair of sine shaped waves. Similarly, in FIG. 3, the cross-sectional profile of the shaft inner diameter  32  relative to dashed lines  39 P is also substantially similar to a pair of sine shaped waves. Alternately, in the embodiment illustrated in FIG. 4, the cross-sectional profile of the shaft outer diameter  30  relative to dashed lines  37 P is substantially similar to three sine shaped waves. Somewhat similarly, in FIG. 4, the cross-sectional profile of the shaft inner diameter  32  relative to the dashed line  39 P is also substantially similar to three sine shaped waves. 
     In the embodiments provided herein, the shaft tip section  28  extends from approximately 0 to 4 inches, the shaft intermediate section  26  extends from approximately 4 to 38 inches, while the shaft butt section  24  extends from approximately 38 to 58 inches. 
     As provided herein, the club shafts  18  can be made by sequentially wrapping a plurality of patterns  38  (shown in FIG. 8) onto a form  40  (shown in FIGS.  5 - 7 ). FIGS. 5-7 each illustrate an alternate, cross-sectional view of a form  40  positioned on a graph. Each form  40  illustrated in FIGS. 5-7 is a mandrel which is substantially solid, rod shaped and has a circular cross-section. The form  40  includes a form butt section  42 , a form intermediate section  44 , and a form tip section  46 . The form intermediate section  44  attaches the form butt section  42  and the form tip section  46 . The form  40  has a form outer diameter  48 , a form length  50  and a form longitudinal axis  52 . 
     A cross-sectional profile of each of the three forms  40  is provided in FIGS. 5-7 respectively. Importantly, the form  40  illustrated in FIG. 5 can be used to make the club shaft  18  illustrated in FIG.  2 . Similarly, the form  40  illustrated in FIG. 6 can be used to make the club shaft  18  illustrated in FIG.  3 . Further, the form  40  illustrated in FIG. 7 can be used to make the club shaft  18  illustrated in FIG.  4 . 
     The form outer diameter  48  is substantially equal to the shaft inner diameter  32  of the club shaft  18 . To manufacture the unique club shafts  18  provided above, the form intermediate section  44  of each form  40  has a unique shape. To highlight the unique shape, dashed lines  54 P in FIGS. 5-7 illustrate how the form outer diameter  48  would appear if the form intermediate section  44  had a substantial linear taper. 
     It should be noted from FIGS. 5-7, that the form outer diameter  48  of the form intermediate section  44  tapers from the form butt section  42  to the form tip section  46 . Importantly, the rate or amount of taper varies along the entire form intermediate section  44 . Thus, the slope or pitch of the taper relative to the form longitudinal axis  52  varies along the form intermediate section  44 . Further, the slope of the taper of the form intermediate section  44  relative to the form longitudinal axis  52  near the form tip section  46  and the form butt section  42  is approximately zero. This feature facilitates the manufacturing of a club shaft  18  having a smooth, continuous shape and eliminates any abrupt transitions in the club shaft  18 . 
     Stated another way, the form outer diameter  48  includes a superficially segmented, undulating or curved surface profile. FIGS. 5-7 illustrate three preferred embodiments of the form  40 . In the embodiment illustrated in FIG. 5, the cross-sectional profile of the form outer diameter  48  relative to dashed lines  54 P is substantially similar to a single, rounded sine wave. Alternately, in the embodiment illustrated in FIG. 6, the cross-sectional profile of the form outer diameter  48 , relative to dashed lines  54 P is substantially similar to a pair of sine waves. Still alternately, in the embodiment illustrated in FIG. 7, the cross-sectional profile of the form outer diameter  48  relative to dashed lines  54 P is substantially similar to three sine waves. 
     It is important to recognize that the embodiments provided in FIGS. 5-7 are for exemplary purposes only and can be varied to alter the performance characteristics of the club shaft  18 . 
     The patterns  38  are sequentially wrapped around the form  40  to form the club shaft  18 . The number, size, shape and thickness of the patterns  38  can vary. Typically, each pattern  38  is a thin sheet of material having a thickness of between approximately 0.003 inches to 0.008 inches. Each pattern  38  is preferably impregnated with a resin to hold the patterns  38  together after heat cure to form the club shaft  18 . Each pattern  38 , for example, can be made of S-Glass, 34-700 high tensile, high strength, graphite, high modulus graphite and/or aramid fiber. The material for the patterns  38  can be purchased from Newport Adhesives and Composites, located in Irvine, Calif. The patterns  38  illustrated in FIG. 8 are merely representative of suitable patterns  38 . For example, the patterns  38  can also include ±angle plys (not shown), strength plys (not shown), and/or one or more tip inserts or outserts (not shown). 
     The manufacturing processes provided herein allows the manufacturer to specifically, uniquely tailor the characteristics of the club shafts  18  by adjusting the shape of the form intermediate section  44 . This allows the manufacturer to finely tune the performance and strength characteristics of the club shafts  18 . 
     Importantly, other manufacturing processes can be used to manufacture a club shaft  18  in accordance with the present invention. In particular the form  40  could be a fluid filled bladder (not shown) instead of a mandrel  41 . Alternately, one or more filaments  56  (illustrated in FIG. 9) could be wrapped around the form  40  instead of the patterns  38 . Still alternately, each club shaft  18  could be molded from a metal or other material in a closed die  58  (illustrated in FIG.  10 ). 
     While the particular club shafts  18 , as herein shown and disclosed in detail, are fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.