WO1997023258A1

WO1997023258A1 - Golf club having a flex zone

Info

Publication number: WO1997023258A1
Application number: PCT/US1996/020928
Authority: WO
Inventors: Randy M. Beck; Tod Boretto
Original assignee: Horizon Sports Technologies, Inc.
Priority date: 1995-12-22
Filing date: 1996-12-20
Publication date: 1997-07-03
Also published as: AU1570297A

Abstract

A golf club shaft (2) has a section of reduced diameter (10) or flex zone in which there is a uniform tubular midsection. The flex zone (10) is a zone in increased, concentrated flexibility which improves the swing characteristics of the golf club since there is less flexing at the tip of the shaft (2) under dynamic load. The fibrous structure of the shaft (2) is continuous throughout the flex zone (10) and the shaft sections immediately preceding and following it. In this way the structural integrity of the shaft (2) is not sacrified for the flex zone (10). A preferred process of manufacturing such shafts (2) keeps the fibrous structure of the shafts (2) intact while creating the flex zones. The process also results in considerable savings in structural materials used to make a shaft resulting in a shaft that is much lighter than prior art shafts having reduced diameter sections. The process involves wrapping resin impregnated composite material over a bladder covering an elongated mandrel that is fitted for compressed air. The pressurized air expands the bladder and thereby the composite material making it conform to a mold having the desired shape of the shaft. After curing, the bladder and mandrel are removed leaving a golf shaft of this design. An alternate method uses expandable foam to press the composite material against the mold.

Description

GOLFCLUBSHAFTHAVINGAFLEXZONE

BACKGROUND OF THE INVENTION

This invention relates in general to golf club shafts and more specifically to such shafts having a section of reduced diameter for increased flexibility in the section, and to methods of forming a shaft having such a reduced diameter section.

The flex characteristics of a golf club shaft has a significant impact on the kinetic energy and trajectory imparted to a golf ball by the club. Such shafts have progressed from wood to tubular metal and are now being molded from composite materials. Conventionally shafts are straight and taper down continuously from the end closest to the golfer, often called the "butt" of a shaft, to the end to which the clubhead is attached, often called the "tip" of a shaft. A problem with continuous taper shafts is that during the swing there is considerable flexing of the shaft in the tip region which is conventionally the most narrow in diameter. This tip region flexing will vary under differing swing speeds and in turn will vary the angle of attack of the clubhead at impact. Variations in the angle of attack increase the dispersion pattern of the balls hit down range and makes the entire club less controllable.

To solve this problem of deflection and lack of stability in the shaft, the common approach has been to enlarge the overall shaft diameter and increase either the shaft wall thickness or fiber modulus or fiber orientation in the structure. However when these approaches are employed, the overall stiffness of the shaft increases to the point where the shaft becomes too stiff and feels

"boardy." Thus the feel and playability are sacrificed.

Another approach has been to construct the shaft having a section which is more flexible than the other sections of the shaft. The more flexible section allows the shaft to flex in that location and allows the tip to be ore rigid and resistant to flexing during a swing. However, in constructing this flexible section, composite material in the section is conventionally excised, such as by cutting or grinding, to reduce the diameter of the section to the extent that the section has the low rigidity and high flexibility characteristics desired. However this machining away of composite material leaves the shaft greatly weakened in the excised section. This results in frequent failures of the shaft in the section. This invention presents a novel method of constructing a shaft having an increased flexibility section of reduced diameter without significantly weakening the structure of the shaft, and with the further advantage of a reduction in shaft weight. Other advantages and attributes of this invention will be readily discernable upon a reading of the text hereinafter.

SUMMARY OF THE INVENTION

An object of this invention is to provide a novel golf shaft having improved swing characteristics.

An additional object of this invention is to provide a golf shaft having a "flex zone" (a section of reduced diameter as described hereinafter) , and consequently reduced rigidity in the flex zone, without significantly reducing the structural integrity of the shaft.

An additional object of this invention is to provide a golf shaft as described above also having reduced weight as compared to prior art shafts having reduced diameter sections. An additional object of this invention is to provide a golf shaft having a flex zone including butt-side and tip- side transition sections (as described hereinafter) with the taper, i.e. the rate of change of shaft diameter, of the tip-side section being faster than the taper of the butt-side section to achieve a more advantageous stress transfer to and from the flex zone. An additional object of this invention is to provide a full complement of golf club shafts each having a flex zone, the zones all being disposed a uniform distance from the butts of the shafts. An additional object of this invention is to provide a full complement of golf club shafts each having a flex zone, the zones being disposed at progressively increasing distances from the butts of the shafts, the distance increasing from the longest shaft to the shortest. An additional object of this invention is to provide a full complement of golf clubs each having a flex zone, the zones being disposed at progressively increasing distances from the butts of the shafts, the distance increasing from the shortest shaft to the longest. An additional object of this invention is to provide a method of manufacturing a golf shaft having a flex zone in which the longitudinal fibers of the composite material used to mold the shaft are homogenous for the entire length of the shaft, the fibrous structure being continuous and uncut throughout the flex zone and the sections preceding and following.

A further object of this invention is to provide a method of manufacturing a golf shaft having a flex zone, and having reduced weight over prior art shafts having reduced diameter sections.

These objects, and other objects expressed or implied in this document, are accomplished by a golf shaft having an elongated tubular body, preferably tapered to be narrower at the tip than at the butt and having a flex zone of increased flexibility. As used herein the term "shaft" refers to the generally tubular shaped body of the preferred embodiment of the golf shaft. The flex zone is defined by the body intermediate the butt end and the tip end, and includes a butt-side transition section having an inward taper, a tip-side transition section having an outward taper, and a section intermediate the transition sections. The body has a fibrous structure and the fibrous structure of flex zone is homogenous and continuous with the sections of the body bordering on the flex zone. Preferably the section intermediate the transition sections has a constant diameter, and the magnitude of the taper of the tip-side transition section is greater than the magnitude of the taper of the butt-side transition section, preferably substantially twice the magnitude of the taper of the butt-side transition section. This invention includes a set of golf club shafts of progressively increasing length having all disposed a uniform distance from the butt ends of their respective bodies. Alternately the set can have flex zones disposed at progressively increasing distances from the butt ends of their respective bodies, the distances increasing from the longest body to the shortest body or the distances increasing from the shortest body to the longest body. Two methods of making a shaft with a flex zone according to this invention are also explained.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an elevational view showing a preferred embodiment of a shaft with a reduced diameter section, i.e. , a flex zone.

Figure 2 is a partial cross-sectional view of a prior art golf shaft having a reduced diameter section and made from composite materials.

Figure 3 is a partial cross-sectional view of the reduced diameter section of the preferred embodiment of a golf shaft according to this invention.

Figure 4 is an elevational view of a set of golf shafts having a flex zone disposed a fixed distance from the grips.

Figure 5 is an elevational view of an alternate set of golf shafts in which the flex zones are progressively farther from the grips going from the shortest shafts to the longest.

Figure 6 is an elevational view of an alternate set of golf shafts in which the flex zones are progressively farther from the grips going from the longest shafts to the shortest.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to Figure 1, a first preferred embodiment of a golf shaft according to this invention is illustrated. A shaft 2, which is tubular in construction and is symmetrically formed around a longitudinal axis 4, is preferably constructed of a composite material which could be comprised of graphite (carbon fibers) , aramid fibers, fiber glass fibers or a combination of these fibers or other fiber type filaments impregnated with an epoxy thermoset resin or a thermoplastic resin. The shaft is slightly tapered being widest at the butt 8 and most narrow at the tip 6. During final shaft assembly, a golf grip will be installed over the butt end of the shaft to cover a grip section 14. Between the grip section and the tip, the shaft 2 has a section 10 of reduced diameter, i.e., a flex zone giving it a pinched appearance. This "pinch" in the shaft reduces the diameter and decreases its stiffness in that region. By reducing the bending stiffness of the shaft under load, the shaft will concentrate the maximum area of deflection where the lowest area of stiffness is located.

Referring again to Figure 1, the flex zone 10 has a tubular "gauge" section 12 of essentially constant diameter significantly reduced from the diameter of the shaft sections immediately preceding and immediately following the flex zone. The gauge section preferably varies in length from approximately one-half inch to three inches, but could be longer. Immediately preceding the gauge section is a butt-side transition section 15A, and immediately following the gauge section is a tip-side transition section 15B, both of which are part of the flex zone. The butt-side transition section begins at a point where the in-taper, i.e. reduction in diameter, of the shaft 2 noticeably increases over the general taper of the shaft, creating an annular apex, such as at 18. The taper of the butt-side transition section is preferably constant until it ends at the upper limit 22 of the gauge section. The tip-side transition section begins at the lower limit 20 of the gauge section and tapers out, i.e. increases in diameter, at a preferably constant rate until it reaches a lower annular apex 16 at which the general taper of the shaft resumes.

The transition sections are used to avoid concentrating the load imparted by a swing at the borders of the flex zone. They avoid what is commonly called

"stress risers" that could otherwise occur if the borders were not so tapered. Preferably the fastest taper, i.e. the highest rate of change of shaft diameter, occurs in the tip-side transition section in order to rapidly transfer the stress of the swing away from the tip to the gauge section. Preferably the butt-side transition section has a more gradual taper to allow a more gradual dissipation of the stress toward the butt of the shaft. It has been found that taper rates in the range of 0.050 to 0.150 inches of diameter per inch of shaft length are preferable, depending on the dimensions of the shaft and the location of the flex zone on the shaft, with the taper of the tip-side transition section preferably being twice the taper of the butt-side transition section. The diameter of the gauge area 12 preferably varies from 0.050" to 0.300" less than the diameter of the shaft at the annular apexes 16 or 18. The 0.050" minimum reduction in diameter is needed to reduce the stiffness in the flex zone sufficiently to allow for a significant flex deflection of the shaft. Greater diameter reductions provide more flexible gauge sections. The small diameter in the gauge section allows for the maximum deflection under load over the entire length of the shaft. This translates into a pure lever action when the shaft and club head are being swung dynamically. This lever action eliminates the flexing in the tip region commonly found with straight tapering shafts. The flex curvature of the shaft will vary under different swing speeds changing the angle of attack of the clubhead at impact.

Unlike standard tapered shafts that are larger in the butt region than the tip region with a constantly decreasing diameter from the butt to the top, this invention allows the shaft to be very stable with a linear deflection curve that has the proper and acceptable feel during the swing. The linearity of the shaft is due to the fact that the deflection of the shaft can be controlled over a small given span or flex zone.

The flex zone can be placed at any location up and down the length of the shaft to control the specific flex and launch angle desired. For example, an entire set of shafts for irons could be produced with flex zones disposed a uniform distance from the butts of their respective shafts, as illustrated in Figure 4. Alternatively the set may have progressively descending flex zones as illustrated in Figure 5, or progressively ascending flex zones as illustrated in Figure 6. Referring to figure 2, the prior art for construction of composite material golf shafts 40 having reduced diameter sections is illustrated. These shafts are constructed from layers of fiber materials 42 which are built up in incomplete layers. For example, different types of fiber materials may be used in a reduced diameter section 44 than in the remainder of the shaft. Conventionally the composite material is built up over a removable mandrel to the desired thickness 46 and cured in a mold. After curing, the shafts are then cut or machined to remove composite material from a section of the shaft 40 down to a core 52 to create a reduced diameter section 44. As can be seen, composite fibers through the two transition sections, 54 and 56, have been cut away, including structural longitudinal fibers that previously spanned the reduced diameter section. This may be effective for reducing rigidity, but it seriously weakens the structural strength of the shaft. This is because the structural strength of a golf shaft or any other composite structure is due primarily to the continuous nature of the fibers within the structure, and once the fiber continuity is destroyed, the structural values are significantly reduced. Under load, such as during a swing, the majority of the stress on the shaft will be concentrated in the reduced diameter section and the shaft will have a high propensity to break or permanently bend in the section.

The novel processes of manufacturing a golf shaft according to this invention do not create flex zones by excising structural material, as in the prior art. The novel processes avoid cutting or otherwise interrupting the fibrous structure of the shaft with the result that the shaft retains its structural integrity while also having the desired dynamic characteristics. The material used during the processes to make the shafts can be comprised of graphite (carbon fibers) , aramid fibers, fiber glass fibers or a combination of these fibers or other fiber type filaments impregnated with an epoxy thermoset resin or a thermoplastic resin.

The preferred process begins with cutting impregnated material called "prepreg" into desired fibrous patterns and wrapping the prepreg over a resilient latex or silicone bladder covering an elongated mandrel, preferably a steel mandrel. The mandrel, bladder and wrapping are at least as long as the shaft being made. The mandrel has a compressed air inlet at a butt end, the inlet communicating with a central air passage defined by the mandrel and air holes distributed along the mandrel, all for injecting pressurized air into the bladder to expand it. The wrapping, bladder, and mandrel combination is then placed into an elongated mold that conforms to the desired shape of the shaft including the flex zone. The mold can be assembled from multiple pieces, e.g. two pieces, which can be clamped together, as by a clamping press. Compressed air is then injected into the mandrel causing the bladder to expand. The expansion of the bladder forces the -en_¬ wrapping against the confines of the mold, forcing it to assume the exact geometry defined by the confines of the mold. Under heat and pressure, the material expands and is cured in the mold, replicating its shape. After the cure cycle is complete, the bladder is deflated and the mold is opened. The cured wrapping, i.e. the newly molded shaft, is then released from the mold, and the mandrel and bladder are removed. In this way the flex zones are created during the shaft molding process and are not, as in the prior art, machined afterwards.

Figure 3 illustrates, by partial cross-section, a shaft produced by the above-described process. In this shaft the longitudinal fibers 74 of the composite material have been molded into the flex zone 10 rather than being cut and trimmed away as is done in the prior art (Figure

2) . This keeps the fibrous structure intact throughout the shaft to give it maximum strength. As can be seen the fibrous structure of the flex zone is homogenous and continuous with the fibrous structure of the portions of the shaft immediately preceding and immediately following the flex zone. In other words, the wall of the shaft is of uniform thickness and construction before, through and after the flex zone, and the fibrous structure which strengthens the shaft is not interrupted by the flex zone. Furthermore, this method of manufacturing allows the shaft to be constructed with less material than shafts built according to prior art, resulting in shafts that weigh less. The gaps between the diameter 70 of a mandrel (shown in phantom) used to make the shaft and the inside diameter 72 of the shaft represent the savings in material used.

These material savings constitute a considerable reduction in weight over prior art golf shafts. For a typical shaft, the weight reduction approaches 40 grams. This is a very significant reduction in view of the fact that most graphite golf shafts weigh between 60 to 80 grams. This amounts to a reduction of approximately one-half to two- thirds of the weight over shafts made from the same material but using prior art methods. This weight reduction relates to improved performance characteristics as a golf club shaft.

An alternate method of creating the cross-sectional shape of the preferred embodiment of the golf shaft 2 of Figure 3 is by using expandable foam. The composite prepreg material is wrapped around a mandrel and encased in a mold, the confines of which define the outside shape of the shaft, including the flex zone. The mandrel is then removed and replaced in the wrapping by a heat expandable foam. Heat is applied to expand the foam, and the expanding foam forces the wrapping against the confines of the mold, and forces it to assume the shape of the mold. After the wrapping is cured and removed from the mold, the foam material is chemically removed. Alternately it can be left in place as a lightweight filler.

The foregoing description and drawings were given for illustrative purposes only, it being understood that the invention is not limited to the embodiments disclosed, but is intended to embrace any and all alternatives, equivalents, modifications and rearrangements of elements falling within the scope of the invention as defined by the following claims. WE CLAIM:

Claims

1. A golf club shaft comprising: (a) an elongated, hollow tubular body having a butt end and a tip end, the body having a fibrous structure;

(b) a flex zone defined by the body intermediate the butt end and the tip end, the flex zone comprising: (1) a butt-side transition section having an inward taper, (2) a tip-side transition section having an outward taper, and (3) a section intermediate the transition sections; (c) the fibrous structure of flex zone being homogenous and continuous with the sections of the body bordering on the flex zone.

2. The shaft according to claim 1 wherein the section intermediate the transition sections has a constant diameter.

3. The shaft according to claim 1 or 2 wherein the magnitude of the taper of the tip-side transition section is greater than the magnitude of the taper of the butt-side transition section.

4. The shaft according to any preceding claim wherein the magnitude of the taper of the tip-side transition section is substantially twice the magnitude of the taper of the butt-side transition section.

5. The shaft according to any preceding claim wherein the magnitude of each taper is within a range of 0.50 to 0.150 inches of body diameter per inch of body length. 6. The shaft according to any preceding claim wherein the length of thesection intermediate the transition sections is within a range of 0.5 to 3 inches.

7. The shaft according to claim 2 wherein the diameter of the section intermediate the transition sections is 0.05 to

0.3 inches less than either section of the body bordering on the flex zone.

8. A set of golf club shafts of progressively increasing length, each shaft comprising:

(a) an elongated, hollow tubular body having a butt end and a tip end, the body having a fibrous structure; (b) a flex zone defined by the body intermediate the butt end and the tip end, the flex zone comprising:

(1) a butt-side transition section having an inward taper,

(2) a tip-side transition section having an outward taper, and

(3) a section intermediate the transition sections;

(c) the fibrous structure of flex zone being homogenous and continuous with the sections of the body bordering on the flex zone.

9. The set of shafts according to claim 8 wherein the flex zones are all disposed a uniform distance from the butt ends of their respective bodies.

10. The set of shafts according to claim 8 wherein the flex zones are disposed at progressively increasing distances from the butt ends of their respective bodies, the distances increasing from the longest body to the shortest body. -lS- ll. The set of shafts according to claim 8 wherein the flex zones are disposed at progressively increasing distances from the butt ends of their respective bodies, the distances increasing from the shortest body to the longest body.

12. A method of constructing a golf club shaft having a flex zone comprising the steps of:

(a) enveloping an elongated mandrel with an inflatable bladder, the mandrel having a fitting external to the bladder for communicating with a source of a pressurized gas and means for distributing the gas through and along the mandrel and into the bladder,

(b) wrapping the bladder with a uniform thickness of composite material impregnated with a resin, the bladder, wrapping and mandrel being at least as long as the shaft being constructed,

(c) encasing the wrapped mandrel in an elongated mold, the confines of the mold conforming to the desired outside shape, including a flex zone, of the shaft being constructed,

(d) applying a gas to the mandrel fitting of sufficient pressure to inflate the bladder and forcibly press the wrapping against the confines of the mold,

(e) curing the wrapping in the mold, (f) removing the cured wrapping from the mold, and

(g) removing the mandrel and bladder from the cured wrapping.

13. The method of claim 12 wherein the composite material is impregnated with a thermoplastic resin.

14. The method of claim 12 wherein the composite material is impregnated with a thermoset resin. 15. A method of constructing a golf club shaft having a flex zone comprising the steps of:

(a) wrapping an elongated mandrel with a uniform thickness of composite material impregnated with a resin, the wrapping and mandrel being at least as long as the shaft being constructed,

(b) encasing the wrapped mandrel in an elongated mold, the confines of the mold conforming to the desired outside shape, including a flex zone, of the shaft being constructed,

(c) replacing the mandrel with a heat expandable material,

(d) applying heat to cause the material to expand and exert sufficient pressure to forcibly press the wrapping against the confines of the mold, (e) curing the wrapping in the mold,

(f) removing the cured wrapping from the mold.

16. The method of claim 15 wherein the expanded material is removed from the cured wrapping by chemical action.

17. The method of claim 15 wherein the expanded material is a foam that is left in the cured wrapping as a light weight filler.