Abstract:
An annular or porous insert of predetermined weight is mounted at a predetermined location within a tubular golf shaft, the shaft being of any suitable material including either metal or graphite. The insert is circumferentially uniform and is dimensioned so that it does not of itself have an impact on the swing characteristics of the shaft, other than the swingweight and/or the total weight of the manufactured shaft. In this way the swingweight and/or the total weight of the shaft can be altered without having to change the construction of the shaft. Furthermore the insert is simple to install at any desired location and it does not interfere with the assembly of the finish club, nor does it violate the standards of the USGA.

Description:
[0001]    This application claims the benefit of U.S. Provisional Application No. 60/060115 filed Oct. 3, 1997.  
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to a golf club shaft having improved swing characteristics and more particularly to a method and device for altering or adjusting the weight characteristics of a golf club shaft without affecting other swing characteristics.  
           [0003]    Golf clubs are typically manufactured by assembling separately manufactured grips, shafts and heads. Thus, the swing characteristics of a given club arise from the combined effects of these three elements. Although there are many choices of heads, grips and shafts available to club makers, it is frequently the case that the specific components combined in a particular club may produce a club having swing characteristics that are not desirable.  
           [0004]    A characteristic of particular importance is the swingweight of a club, which is a measure of the effect of the distribution of the total weight of the club over its length. This is a swing characteristic frequently used in fitting players with suitable clubs. The swingweight is determined by the combined weight of the selected head, shaft and grip as well as the distribution of the weight of each component over its respective length. There is today a strong trend towards heavier golf club heads which tend to produce longer distances from a given swing. However, these heads contribute significantly to an increased swingweight and, when combined with the swingweight contribution of available shafts, produce a total club swingweight that is too high for the majority of golfers. Even in the case of custom shafts having swing characteristics defined in advance by the club maker, the final club head chosen by the club maker is often heavier than originally planned and, if combined with the custom shaft, the club&#39;s swingweight would be excessive. Accordingly, there is a need for a method and device which would permit a manufacturer to adjust the weight distribution of a shaft so as to accommodate heavier club heads while still maintaining a desirable club swingweight without affecting other swing characteristics.  
           [0005]    Another problem encountered in shaft manufacture is that of adjusting the total weight of a given shaft design as may be necessary for a variety of reasons. For example, very low handicap players may, in seeking specific swing characteristics, wish to use a particular shaft tube construction that has a lower total tube weight than a previously used construction. At the same time, they want the new shaft to have the same shaft weight as the previously used construction because of its influence on the “feel” of a club when making a shot. In another instance, if a new shaft design turns out to be lighter in weight than that specified by a club maker, it would be very desirable if a shaft manufacturer could simply add a suitable weight rather than redesign the shaft, provided that this could be done without affecting other swing characteristics. In still another instance, it may be desirable for high handicap players to add a significant amount of weight near the butt end of the shaft so as to permit the use of heavier heads, with their attendant potential for greater distance, while still maintaining a reasonable swingweight. In all of these cases, it&#39;s desirable that a method and device be provided for adding weight to a given shaft tube, either with or without modifying the swingweight.  
           [0006]    In the past, various proposals have been made for adding weight to a golf club for the purpose of adjusting selected aspects of the swing characteristics. However, these designs have generally been focused in other directions and have not dealt with those characteristics of a swing that are of most importance to both the club manufacturer and the user, namely the swingweight and the flex characteristics. Accordingly, there is a clear need for a method and device that can be used by a shaft manufacturer to adjust the swingweight of a shaft and/or to adjust the total weight of a shaft without affecting other swing characteristics such as stiffness and torsional rigidity.  
           [0007]    In addition to the failure of the prior art to address the most basic elements of shaft design as noted above, the designs of the prior art have failed in several other respects. First, the shaft manufacturer requires a simple device and method that can be easily used without adding a great deal of complexity to the shaft manufacturing process and that can adjust the weight characteristics over a wide range. Of course, as previously noted, this must still be done without affecting other swing characteristics. Many prior art designs do not meet these objectives.  
           [0008]    Secondly, the normal process of club manufacture involves the installation of a club head on the lower end of the shaft followed by the installation of a grip on the other. If a closed plug seals the shaft at any point along its length, as has frequently been proposed in the past, the attachment of the head will trap and compress air within the shaft. Since most heads are attached by an epoxy adhesive, and since the better epoxy adhesives are slow-curing, the compressed air will move the head away from its desired location unless firm fixturing is used. Since most club assemblers do not use any fixturing at all, this is a serious problem. Other prior art designs involve the attachment of a weight in a sealing manner at the upper end of the golf shaft. These designs also trap and compress air within the shaft, which can force either the weight or the head to move from their desired locations. Thus, designs having these flaws are unacceptable.  
           [0009]    Still other prior art designs exist that use either non-symmetrical or moveable weights either in or on the club. However, virtually all golfers use clubs that are manufactured to the standards established by the United States Golf Association for tournament-qualified clubs. These standards require that the club shaft exhibit uniform properties in all directions from the axis of the shaft and that no moveable parts be included in or on the club. Various designs of the prior art fail to meet these requirements.  
         SUMMARY OF THE INVENTION  
         [0010]    It is a primary purpose and principal object of the present invention to provide a method and device for altering existing weight characteristics of a golf club shaft without affecting the other characteristics of the shaft. It is another object of the present invention to provide a method and device for altering the swingweight and/or the total weight of a golf club without affecting the other swing characteristics of the club.  
           [0011]    A further object of this invention is the provision of a method and device for altering weight characteristics of a golf club shaft as noted above that may be easily used to adjust the weight characteristics over a wide range without adding complexity to either the structure of the club or to the manufacturing process and that further does not interfere with later steps required to complete the assembly of the club.  
           [0012]    Finally, it is an object of this invention to provide a method and a device for achieving the above objectives while still enabling the resultant club to meet the standards of the USGA.  
           [0013]    According to one embodiment of the invention an annular or porous insert of predetermined weight is mounted at a predetermined location within a tubular golf shaft, the shaft being of any suitable material including either metal or graphite. The insert is circumferentially uniform and is dimensioned so that it does not of itself have an impact on the swing characteristics of the shaft, other than the swingweight and/or the total weight of the manufactured shaft. In this way the swingweight and/or the total weight of the shaft can be altered without having to change the construction of the shaft. Furthermore the insert is simple to install at any desired location and it does not interfere with the assembly of the finished club, nor does it violate the standards of the USGA.  
           [0014]    Also, the invention allows for changing the club head weight that can be used with a given golf shaft while still preserving the desired swingweight of the club and the other swing characteristics of the club.  
           [0015]    This invention also comprehends a method of adjusting the swingweight and/or the total weight of a golf club shaft which includes the steps of calculating the swingweight of a shaft and affixing an annular or porous insert within the shaft, the weight and position of the insert being sufficient to modify the swingweight and/or the total weight by a predetermined amount.  
           [0016]    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  
       [0017]    [0017]FIG. 1 is a schematic side elevation view of a golf club shaft used with the invention;  
         [0018]    [0018]FIG. 2 is a detailed perspective of an insert according to the invention;  
         [0019]    [0019]FIG. 3 is a cross-sectional close-up of a part of FIG. 1, showing an insert disposed within the golf shaft; and  
         [0020]    [0020]FIG. 4 is a cross-section of an insert according to another embodiment of this invention.  
     
    
     DETAILED DESCRIPTION  
       [0021]    Referring to FIG. 1, there is shown a golf club  10  having a grip  6 , a head  8  and a tubular shaft  12  which may be graphite or metallic. The club  10  may be a wood club, an iron, or a putter. A cut-away portion of the shaft is shown in FIG. 3 in which a cylindrical insert  14 , according to one embodiment of the invention, is shown disposed within the interior of the shaft  10 . The insert  14  is preferably a cylinder of material weighing in the neighborhood of 1 to 8 grams, although up to 20 grams or more may be used in some cases. The insert is preferably less than 10% of the length of the shaft (which is usually more than 40 inches). Specifically, the insert is preferably within a range of approximately one to three inches in length, so that its presence in the shaft does not have an appreciable impact on swing characteristics of the shaft such as flex, strength and torsional rigidity other than its contribution to the weight distribution and total weight. The insert  14  is preferably in the form of an annular or tubular device having a central opening  16  as shown in FIG. 2.  
         [0022]    The insert  14  has an outer diameter which suitably corresponds to the inner diameter of the shaft in which it is to be used, usually in the range of between 0.400 and 0.600 inches. The density and thickness of such material should be such that it weighs at least approximately 4 grams per inch of material or more. A suitable material, for example, is polyisobutylene. Other elastomeric or foamed materials may also be used. Preferably this material is flexible and has a diameter slightly larger then the internal diameter of the shaft at the point at which the insert is to be placed. An adhesive coating  18  is applied to the exterior of the insert, or it may be included in the material of the insert. When the insert is pressed into place at the desired location in the shaft, the compression of the material holds it in place until the adhesive is cured, either by heat or time. Anaerobic adhesives which cure in the absence of air could also be used. In this case, it is not necessary that the material be flexible, although it is still preferred to compensate for variations in the internal diameter of the shaft. This is of greater importance with graphite or fibrous shafts.  
         [0023]    Still another embodiment of the invention is an insert  20  having a metal ring or cylinder  22 , the ring being covered with a layer of flexible material  24  to produce the configuration shown in FIG. 4. The surface is coated with an adhesive  26 , as in the previous embodiment, or it may be impregnated into the layer  24 . This ring or cylinder is pressed to a desired location within the shaft, accommodating variations in the ID of the shaft. As in the previous embodiment, the insert  14  is preferably dimensioned so that its outer diameter is slightly larger than the inner diameter of the tubular shaft  10 , thereby affording a tight fit within the shaft wherever it is intended to be placed. The internal wall surface of the tubular shaft will compress the weighted insert and hold it in place at the desired location until the adhesive on the outside surface of the insert cures, thus permanently fixing the insert in place. As above, the use of a fast-curing anaerobic adhesive may reduce or eliminate the need for compressibility. It is possible, too, to dispense with the curable adhesive so that only the forces of compression hold the insert in place, in which case the tubular insert may be dimensioned to be larger in diameter than when it is used with an adhesive, thus increasing the compression forces on the insert.  
         [0024]    In order to conform to USGA standards, it is particularly important that the mechanical properties of the insert be circumferentially uniform at any radial distance from its center. This is most easily achieved by making the insert of uniform cylindrical or annular parts.  
         [0025]    Any installed insert must allow air to be transmitted through the tubular shaft so as not to cause pressurization of air in the shaft between two lightly fitted parts, such as the insert and the club head, since this could cause movement of either part from its desired location. The annular insert  14  provides a central opening for this purpose, or the material used as the insert may be pervious to air (a porous material, for example) or alternatively a small bore can be provided in the center of the insert to allow air passage, if it is a closed-cell material.  
         [0026]    As previously mentioned, as much as 20 grams or more of weighted material can be added as an insert in the golf shaft if desired. Thus the shaft can be adjusted to a desired total weight or its swingweight can be matched to a particular head so as to yield a desired swingweight for the finished club. Generally, the insert  14 , in accordance with this invention, is placed toward the butt end of the shaft to reduce the swingweight when the head used with shaft turns out to be too heavy. Conversely, the weighted insert could be moved toward the tip of the shaft if the head is too light, but this is normally not the problem.  
         [0027]    It should be appreciated as well that in the case of designing a given shaft having certain swingweight and swing characteristics, a weighted insert can be used according to the invention at different locations or at different weights so as to produce similar shafts that can be matched with different head weights, so that the golf clubs using the various heads and corresponding shafts in accordance with the invention are then identical in swing characteristics and have the same swingweight.  
         [0028]    While it is a primary purpose of the invention to adjust the swingweight of a golf shaft without affecting the other swing characteristics of that shaft, it is also possible within the context of the invention to use the insert to increase total shaft weight without affecting other swing characteristics of the shaft, when this is desirable.  
         [0029]    To further illustrate and explain the present invention, and to set forth a particular preferred embodiment, a brief reference to certain aspects of the method of determining swingweight used by the golfing industry follows. In fact, two different scales, the Official Scale and the Lorythmic Scale, are used widely in the industry to determine the swingweights of shafts and clubs. While the results produced by these two scales differ, both methods use a fulcrum located in the upper half of the length of the shaft. In particular, the Official Scale uses a fulcrum located at 12 inches from the butt end of the shaft while the Lorythmic Scale uses a fulcrum located 14 inches from the butt end of the shaft. Other swingweight scales in use also rely on a fulcrum at 14 inches from the butt end. Thus, while differing in detail, both methods compare the effect of a short portion of a club including its grip with that of a long portion of the club including its head to determine the swingweight. Of course, either of these analyses applied to a shaft will determine the swingweight of the shaft, and thus its contribution to the swingweight of the finished club.  
         [0030]    In this context, a preferred embodiment of the method of this invention involves the steps of reducing the swingweight contribution of a given shaft to the swingweight of a finished club by placing an insert of the type previously described at a location between the fulcrum as selected by the system being used and the butt end of the shaft. Specifically, the weight and the location of the insert are such as to reduce the swingweight of the shaft by a desired amount so as to accommodate it to a particular selected club head.  
         [0031]    To more specifically illustrate the effect of the insert and the method of this invention, it has been found that mounting 1 gram of weighted material a distance of 12 inches from the existing fulcrum of a golf shaft (in either system) moves the fulcrum for that shaft ⅛of an inch. Mounting an 8 gram insert at the same distance moves the fulcrum 1 inch. Of course, mounting an insert at the fulcrum will simply increase the total weight without changing the swingweight.  
         [0032]    Thus, the insert and method of this invention enable the adjustment of a given shaft so that it can accommodate a variety of different club heads while still maintaining a swingweight of a particular value or within a preferred range of values.  
         [0033]    The foregoing relates to a preferred exemplary embodiment 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.