Patent Publication Number: US-2004043825-A1

Title: Golf club shaft set

Description:
FIELD OF INVENTION  
       [0001] The present invention relates to golf club shaft sets, and more particularly, to a golf club shaft set including shafts with composite first ends and metal second ends wherein the length of the metal tip end is inversely proportional to the overall length of the shaft.  
       BACKGROUND OF THE INVENTION  
       [0002] Two types of shafts dominate the golf club shaft market. The first type of shaft is made entirely of metal such as high strength alloy steel. The second type of shaft is made entirely of a composite such as graphite.  
       [0003] Metal shafts are generally regarded as being relatively heavy but provide high torsional stiffness. This results in a playability which yields accurate ball control and good feel but may limit club head speed and hence distance. It can also be made difficult to obtain a high tip flexibility with metal shafts compared to composite shafts which can compromise ball trajectory.  
       [0004] Composite shafts are generally regarded as being relatively light with more flexible tips which can result in a playability which yields higher club head speed and more distance as well as a higher ball trajectory. However, because composite shafts are not torsionally very stiff, composite shafts are also regarded as being somewhat limited in terms of accurate ball control and feel.  
       [0005] To take advantage of the separate benefits of metal and composite shafts while minimizing their deficiencies, a multiple material golf club shaft has recently been introduced to the market. A multiple material shaft is made partially of metal and partially of composite. In other words, a first portion of the shaft is formed of metal, a second portion of the shaft is made of composite, and the two portions are coupled together.  
       [0006] Multiple material shafts are generally regarded as being both lightweight and resistant to torque. This enables the generation of more club head speed than an all metal shaft and more accuracy than an all composite shaft. Nonetheless, it is still desirable to balance the need for distance and accuracy against one another across the entire multiple material shaft set.  
       [0007] For example, lighter and more tip flexible shafts are desirable in the long irons to provide more distance and higher ball trajectory at the expense of a certain degree of accuracy. In contrast, heavier and more torsionally stiff shafts are desirable in the short irons to provide more accuracy and feel at the expense of a certain amount of distance. Medium weight shafts with intermediate torsional stiffness are desirable in the middle irons to provide a compromise between distance and accuracy.  
       [0008] In view of the foregoing, it would be desirable to provide a multiple material golf club set specifically tailored to provide high club head speed in the long irons, high torsional stiffness in the low irons, and a compromise between the two in the middle irons.  
       SUMMARY OF THE INVENTION  
       [0009] A set of golf club shafts is provided including a plurality of shafts progressively increasing in length. Each shaft includes a butt section formed of a first material coupled to a tip section formed of a second, different material. Preferably, the tip section comprises metal while the butt section comprises composite. The length of each tip section is inversely proportional to the overall length of the shaft. As such, the tip sections progressively decrease in length as the plurality of shafts progressively increase in length. The relationship of tip length to butt length or overall length is maintained both in absolute and relative terms. For example, each tip section preferably decreases in length by about 0.5 inch from one club shaft to the next. The length of the tip section of the shortest shaft may be about 30-34% of the entire length of the shaft whereas the length of the tip section of the longest one of the shafts may be about 18-20% of the entire length of the shaft. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0010] The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:  
     [0011]FIG. 1 is a side elevational view of a golf club shaft incorporating the teachings of the present invention;  
     [0012]FIG. 2 is a cross-sectional view of a metal/composite joint of the golf club shaft of FIG. 1; and  
     [0013]FIG. 3 is a side elevational view of a set of golf clubs incorporating the teachings of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0014] The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.  
     [0015] The present invention is directed towards a set of golf club shafts wherein each shaft includes a composite butt section coupled to metal tip section. As each shaft of the set increases in length, the corresponding tip section decreases. This provides at least two advantages. First, because of the different specific gravities of composite material and metal, the longer metal tip maintains or even increases the weight of the shaft as the overall length decreases. Secondly, the increasing length of the metal tip provides more torsional stability as the shaft gets shorter.  
     [0016] 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.  
     [0017] 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 the 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. A preferred embodiment of such a joint  30  is described in U.S. patent application Ser. No. 09/745,001 filed Dec. 21, 2000 which is incorporated by reference herein in its entirety.  
     [0018] Turning now to FIG. 2, the joint  30  of FIG. 1 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 .  
     [0019] 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 .  
     [0020] Turning now to FIG. 3, the set of golf clubs  34  includes a 2-iron  36 , 3-iron  38 , 4-iron  40 , 5-iron  42 , 6-iron  44 , 7-iron  46 , 8-iron  48 , 9-iron  50 , and wedge  52 . The set may also include a gap wedge, sand wedge, and lob wedge in addition to other club types. For example, the golf club shaft set could also include a 1 iron and/or one or more woods. The overall length of each shaft increases from the wedge  52  through the 2-iron  36 . For example, the wedge  52  may have an overall length of 36.5 inches whereas the 2-iron  36  may have an overall length of 40.5 inches.  
     [0021] Each club in the set  34  preferably increases in length over the last consecutive shaft by about 0.5 inch. Conversely, each steel tip section  18  progressively decreases in length as the overall length of the corresponding shaft increases. Accordingly, the steel tip section  18  on the 40.5 inch 2-iron shaft  36  is about 7.5 inches. On the other hand, the steel tip section  18  on the 36.5 inch wedge shaft  52  is approximately 11.5 inches. This inverse relationship of tip length to shaft length continues throughout the shaft set  34   
     [0022] In a preferred embodiment of the present invention, each steel tip section  18  decreases in length by about 0.5 inch from the last consecutive tip section. To compensate for the decreasing length of the tip section  18  (and therefore maintain the desired overall length of the corresponding shaft), the length of the butt section  20  progressively increases as the plurality of shafts progressively increase in length. As such, the tip sections are not only inversely proportional (in length) to the overall shaft length, but also to the butt section length. This is true both in absolute and relative terms.  
     [0023] For example, in the shortest shaft, i.e., the wedge shaft  52 , the tip section  18  accounts for approximately 30-33% of the entire length of the shaft. In contrast, in the longest shaft, i.e., the 2-iron  36 , the tip section  18  accounts for about 17-19% of the entire length of the shaft.  
     [0024] The length of the tip section  18  not only corresponds to the overall length of the shaft, but also to the loft of the club head  14 . The plurality of club heads  14  in the golf club set  34  progressively decrease in loft from the wedge  52  to the 2-iron  36 . Correspondingly, the length of each tip section  18  progressively decreases as the loft of each club head  14  progressively decreases. In contrast to the inverse relationship described above with respect to club length, the relationship to loft is directly proportional.  
     [0025] While a full set of golf club shafts  34  is illustrated in FIG. 3, it should be appreciated that the term set as used herein could comprise as little as two golf club shafts. The only requirement of the set is that the first shaft is longer than the second shaft. In such a set, the first shaft includes a tip section which is shorter than the tip section of the second shaft.  
     [0026] The following table includes an exemplary set of golf clubs in a preferred set incorporating the teachings of the present invention:  
                                                               Total Shaft Length   Club Head Loft   Tip Section           Iron   (inches)   (degrees)   Length                                                            2   40-41   15-19   7.0-8.0           3   39.5-40.5   18-22   7.5-8.5           4   39-40   21-25   8-9           5   38.5-39.5   24-28   8.5-9.5           6   38-39   28-32    9-10           7   37.5-38.5   32-36    9.5-10.5           8   37-38   36-40   10-11           9   36.5-37.5   40-44   10.5-11.5           PW   36-37   44-48   11-12           GW   36-37   48-52   11-12           SW   36-37   53-57   11-12           LW   36-37   58-62   11-12                      
 
     [0027] The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.