Title:
Golf club
Kind Code:
A1


Abstract:
A golf club comprises a shaft formed of a plurality of co-axially disposed tubes connected to one another at a stabilizing joint or joints. Shaft has an upper section forming a grip and a lower section connected to club head. Tubes are parallel-sided and of differing cross-sectional sizes. The lower section is constituted by the tube of smallest cross section. The relative diameters of the tubes are such that the upper end of a tube is receivable within the bore at the lower end of its neighbor. Preferably, the material from which tubes are formed is selected from: (a) a titanium alloy; (b) a combination of (i) an extruded polymeric matrix reinforced with continuous, straight, pre-stressed and tensioned carbon fibers, the fibers being aligned with the longitudinal axis of shaft, and (ii) continuous filament windings that are also pre-stressed, tensioned and unbroken, or (c) a combination of materials from categories (a) and (b).



Inventors:
Tilley, Gordon (Leicestershire, GB)
Application Number:
10/034253
Publication Date:
09/12/2002
Filing Date:
01/03/2002
Assignee:
TILLEY GORDON
Primary Class:
International Classes:
A63B53/10; A63B53/12; (IPC1-7): A63B53/10
View Patent Images:
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Primary Examiner:
BLAU, STEPHEN LUTHER
Attorney, Agent or Firm:
Law Office of Jerome D. Jackson (Alexandria, VA, US)
Claims:

What is claimed is:



1. A golf club shaft for a grip portion and a club head, the golf club shaft comprising: a first tube defining a first end with a first-tube cross-sectional area and a second end with the first-tube cross-sectional area, the first tube thereby being parallel-sided; and a second tube defining a first end with a second-tube cross-sectional area and a second end with the second-tube cross-sectional area, the second tube thereby being parallel-sided, the second-tube cross-sectional area being smaller than the first-tube cross-sectional area, the first and second tubes being co-axially disposed, the golf club shaft being connectable to the grip portion and club head such that a distance between the first end of the first tube and the grip portion is smaller than a distance between the second end of the second tube and the grip portion, and a distance between the second end of the second tube and the club head is smaller than a distance between the first end of the first tube and the club head, wherein the first tube includes a first material selected from the group consisting of: (a) a titanium alloy; or (b) a combination of (i) an extruded polymeric matrix reinforced with continuous, straight, pre-stressed and tensioned carbon fibers, the fibers being aligned with the longitudinal axis of the golf club shaft, and (ii) continuous filament windings that are pre-stressed, tensioned and unbroken, and wherein the second tube includes a second material selected from the group consisting of: (a) a titanium alloy; or (b) a combination of (i) an extruded polymeric matrix reinforced with continuous, straight, pre-stressed and tensioned carbon fibers, the fibers being aligned with the longitudinal axis of the golf club shaft, and (ii) continuous filament windings that are pre-stressed, tensioned and unbroken.

2. A golf club shaft as claimed in claim 1 wherein the first tube is connected to the second tube.

3. A golf club shaft as claimed in claim 2 further including a ferrule acting as a coupling device between the first and second tubes.

4. A golf club shaft as claimed in claim 3 wherein the ferrule includes titanium or an alloy thereof.

5. A golf club shaft as claimed in claim 1 wherein the first end of the second tube is in the second end of the first tube.

6. A golf club shaft as claimed in claim 5, wherein first tube defines an internal diameter, and the first and second tubes overlap by an amount at least four times the internal diameter.

7. A golf club shaft as claimed in claim 1 wherein the first tube is directly connectable to the grip portion.

8. A golf club shaft as claimed in claim 1 wherein the second tube is directly connectable to the club head.

9. A golf club shaft as claimed in claim 1 wherein the first tube includes a combination of: (i) extruded polymeric matrix reinforced with continuous, straight, pre-stressed and tensioned carbon fibers, the fibers being aligned with the longitudinal axis of the golf club shaft, and (ii) continuous filament windings that are pre-stressed, tensioned and unbroken.

10. A golf club shaft as claimed in claim 9, further including a ferrule that overlaps or partially encases the fiber ends.

11. A golf club shaft as claimed in claim 10 wherein the polymeric matrix is a thermosettable material.

12. A golf club shaft as claimed in claim 9 wherein the polymeric matrix is a thermosettable material.

13. A golf club shaft as claimed in claim 9 wherein the first tube is formed by pultrusion and subsequent cutting to a desired length.

14. A golf club shaft as claimed in claim 1 wherein the second tube includes titanium alloy.

15. A golf club shaft as claimed in claim 1 wherein a ferrule is joined to the club head.

16. A golf club shaft for a grip portion and a club head, the golf club shaft comprising: a first tube defining a first end with a first-tube cross-sectional area and a second end with the first-tube cross-sectional area, the first tube thereby being parallel-sided; and a second tube defining a first end with a second-tube cross-sectional area and a second end with the second-tube cross-sectional area, the second tube thereby being parallel-sided, the second-tube cross-sectional area being smaller than the first-tube cross-sectional area, the first and second tubes being co-axially disposed, the golf club shaft being connectable to the grip portion and club head such that a distance between the first end of the first tube and the grip portion is smaller than a distance between the second end of the second tube and the grip portion, and a distance between the second end of the second tube and the club head is smaller than a distance between the first end of the first tube and the club head, wherein the first tube includes a combination of: (i) extruded polymeric matrix reinforced with continuous, straight, pre-stressed and tensioned carbon fibers, the fibers being aligned with the longitudinal axis of the golf club shaft, and (ii) continuous filament windings that are pre-stressed, tensioned and unbroken, and wherein the second tube includes titanium alloy.

17. A golf club shaft as claimed in claim 16 wherein the first tube is formed by pultrusion and subsequent cutting to a desired length.

18. A golf club shaft as claimed in claim 16 wherein the first tube is connected to the second tube, and the golf club shaft further includes a ferrule acting as a coupling device between the first and second tubes.

19. A golf club shaft as claimed in claim 18 wherein the ferrule includes titanium or an alloy thereof.

20. A golf club shaft as claimed in claim 16 wherein a ferrule is joined to the club head.

21. A golf club shaft as claimed in claim 16 further including a ferrule that overlaps or partially encases the fiber ends.

22. A golf club shaft as claimed in claim 16 wherein the first tube is connected to the second tube at a stabilizing joint.

23. A golf club shaft as claimed in claim 16 wherein the first end of the second tube is in the second end of the first tube.

24. A golf club shaft as claimed in claim 23, wherein first tube defines an internal diameter, and the first and second tubes overlap by an amount at least four times the internal diameter.

25. A golf club shaft as claimed in claim 16 wherein the first tube is directly connectable to the grip portion.

26. A golf club shaft as claimed in claim 16 wherein the second tube is directly connectable to the club head.

Description:

[0001] This Application is a Continuation-in-Part of copending Application Ser. No. 09/367,592 (International Application No. PCT/GB98/00530) of GORDON TILLEY filed Feb. 19, 1998 for GOLF CLUB, the contents of which are hereby incorporated by reference.

[0002] This Application claims the benefit of British Application No. 9703429.2 filed Feb. 19, 1997, the contents of which are herein incorporated by reference.

[0003] This Application claims the benefit of British Application No. 9715581.6 filed Jul. 23, 1997, the contents of which are herein incorporated by reference.

BACKGROUND OF TH INVENTION

[0004] 1. Field of the Invention

[0005] The present invention relates generally to a golf club and, more particularly, to a relatively high performance golf club that may be manufactured with relatively low cost.

[0006] 2. Description of Related Art

[0007] U.S. Pat. No. 3,974,012 to Hogarth discloses an apparatus and method for forming tubular tapered shafts for golf clubs, ski poles, fishing rods and such like that uses a thermo-setting resin sheet as a matrix material for supporting a plurality of elongate, laterally spaced parallel fibers of graphite, boron or similar material. The resin sheets are laid over a tapering mandrel and an outer shell is placed over the mandrel with its wrapping of thermosetting resin sheets. The outer shell is connected to the mandrel by a spring-urged collar that acts to draw the shell onto the mandrel as tightly as possible. During cure of the thermnosetting resin sheets, the shell slides relative to the mandrel as the resin contracts, so that the fibers in the resin matrix are tensioned. Tapered tubes formed in this way have a finite length determined by the dimensions of the mandrel and its associated shell.

[0008] U.S. Pat. No. 4,836,545 to Pompa discloses a two piece metallic and composite golf shaft utilising metal for the construction of its lower tip section and a fiber/resin composite for the construction of its upper butt section. The lower metallic tip section may have parallel or tapered sides and has a plurality of diametrally expanding steps at the upper end portion, whilst the upper composite butt section of larger diameter has a lower end reduced in diameter for slidingly fitting into the inside wall of the last (upper) step of the metallic tip section.

[0009] It has long been a desirable goal of golf equipment manufacturers to develop equipment which, by virtue of its design, contributes to improved playing performance on the part of a user without contravening the rules of the game.

[0010] An example of such a development is the golf club formed with a shaft of carbon fiber composite material. Carbon-fiber shafted golf clubs are nowadays produced in large numbers with a reasonable degree of reproducibility and controllable flexibility. High handicap and casual golfers derive the most benefit from clubs fitted with shafts having relatively low stiffness: The behavior of a highly flexible club during a golf swing is such that its flexure contributes to club head speed at the moment of impact with the ball, thereby compensating in part for irregularities in the player's swing.

[0011] Low handicap players will prefer stiffer clubs that enable the “feel” of the playing stroke to be conveyed through the shaft to the player's hands.

[0012] Even though carbon fiber-shafted clubs are increasing in popularity, their high cost means that such equipment is inaccessible to the majority of players.

[0013] The currently-used manufacturing techniques for producing carbon fiber shafted golf clubs are labor-intensive, which contributes to the high cost: Typically, reinforced carbon fiber shafts are made in one piece from loose sheets wrapped around a mandrel. To produce a tapered shaft, a tapered mandrel is required, the usual arrangement being such that the largest diameter section is positioned near the butt or handle section of the shaft, tapering down to the smallest diameter near the point where the shaft is joined to the club head.

[0014] Difficulties are encountered in processing titanium if its alloys are used in the manufacture of golf club shafts. Hence, titanium-shafted clubs are generally very expensive and beyond the normal price range of the average player because of the special measures which are required during processing.

[0015] The shaft portion of relatively small diameter near the head of the club is the weakest point and, inevitably, the shaft is susceptible to breakage-in this region.

[0016] Computer stress analysis shows that the portion of the shaft at which the club head joins the shaft has the greatest stress when a player swings the club and strikes a golf ball. The head tries to break away from the shaft on impact with the stationary golf ball.

SUMMARY OF THE INVENTION

[0017] It is an object of the present invention to provide an improved golf club.

[0018] To achieve this and other objects of the present invention, there is golf club shaft for a grip portion and a club head. The golf club shaft comprises a first tube defining a first end with a first-tube cross-sectional area and a second end with the first-tube cross-sectional area, the first tube thereby being parallel-sided; and a second tube defining a first end with a second-tube cross-sectional area and a second end with the second-tube cross-sectional area, the second tube thereby being parallel-sided, the second-tube cross-sectional area being smaller than the first-tube cross-sectional area, the first and second tubes being co-axially disposed, the golf club shaft being connectable to the grip portion and club head such that a distance between the first end of the first tube and the grip portion is smaller than a distance between the second end of the second tube and the grip portion, and a distance between the second end of the second tube and the club head is smaller than a distance between the first end of the first tube and the club head. The first tube includes a first material selected from the group consisting of (a) a titanium alloy; or (b) a combination of (i) an extruded polymeric matrix reinforced with continuous, straight, pre-stressed and tensioned carbon fibers, the fibers being aligned with the longitudinal axis of the golf club shaft, and (ii) continuous filament windings that are pre-stressed, tensioned and unbroken. The second tube includes a second material selected from the group consisting of (a) a titanium alloy; or (b) a combination of (i) an extruded polymeric matrix reinforced with continuous, straight, pre-stressed and tensioned carbon fibers, the fibers being aligned with the longitudinal axis of the golf club shaft, and (ii) continuous filament windings that are pre-stressed, tensioned and unbroken.

[0019] According to another aspect of the present invention, there is a golf club shaft for a grip portion and a club head. The golf club shaft comprises a first tube defining a first end with a first-tube cross-sectional area and a second end with the first-tube cross-sectional area, the first tube thereby being parallel-sided; and a second tube defining a first end with a second-tube cross-sectional area and a second end with the second-tube cross-sectional area, the second tube thereby being parallel-sided, the second-tube cross-sectional area being smaller than the first-tube cross-sectional area, the first and second tubes being co-axially disposed, the golf club shaft being connectable to the grip portion and club head such that a distance between the first end of the first tube and the grip portion is smaller than a distance between the second end of the second tube and the grip portion, and a distance between the second end of the second tube and the club head is smaller than a distance between the first end of the first tube and the club head. The first tube includes a combination of (i) extruded polymeric matrix reinforced with continuous, straight, pre-stressed and tensioned carbon fibers, the fibers being aligned with the longitudinal axis of the golf club shaft, and (ii) continuous filament windings that are pre-stressed, tensioned and unbroken. The second tube includes titanium alloy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] FIG. 1 is a perspective view of a golf club fitted with a modular shaft in accordance with a first aspect of one embodiment of the present invention;

[0021] FIG. 2 illustrates the construction of a constituent tube of the modular shaft of FIG. 1, showing the arrangement of carbon fiber reinforcement;

[0022] FIG. 3 is a part cross-sectional view showing a stabilizing joint and ferrule; and

[0023] FIG. 4 is another part cross-sectional view showing an arrangement of a reinforcing ferrule at the tip of the shaft where it is joined to a club head;

[0024] FIG. 5 is a view of a sleeve in accordance with an alternate embodiment of the present invention.

[0025] FIG. 6 is a view emphasizing a cross section of a tube in one of the preferred golf clubs.

[0026] The accompanying drawings, which are incorporated in and which constitute a part of this specification, illustrate embodiments of the invention. Throughout the drawings, corresponding parts are labeled with corresponding reference numbers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] FIG. 1 shows a golf club shaft including co-axially disposed tubes 21 and 22 in accordance with one of the embodiments of the present invention. Tubes 21 and 22 are connected to one another at a stabilizing joint or joints, the golf club shaft having an upper section adapted to form a grip portion and a lower section adapted to be connected to a club head, wherein the tubes are parallel-sided and of differing cross-sectional sizes, the arrangement being such that the lower section is constituted by the tube of smallest cross-section, and the relative diameters of the tubes being such that the upper end of a tube is receivable within the bore at the lower end of its neighbor; characterized in that each tube includes (a) a titanium alloy; or (b) a combination of (i) an extruded polymeric matrix reinforced with continuous, straight, pre-stressed and tensioned carbon fibers, the fibers being aligned with the longitudinal axis of the golf club shaft, and (ii) continuous filament windings that are pre-stressed, tensioned and unbroken.

[0028] One preferred form of the tube material designated as “b” above is formed by pultrusion. (Pultrusion is sometimes referred to as “pull-winding.”). In this process, the fibers in the tube are continuous, by which is meant they are never cut until the manufacture of the tube is complete. The fibers are maintained under tension whilst passing through the mould or die at the final moulding and polymerisation stage which forms the tube. As the name of the process suggests, they are in fact “pulled” through the mould under tension to achieve the ultimate alignment and straightness in one continuous operation.

[0029] More specifically, to manufacture the preferred golf clubs, a long tube is formed by pultrusion, and the long tube is subsequently cut into a plurality of shaft tubes having the desired length.

[0030] In conventional extrusion processes, a tube would be formed by pushing the material through a mould or die using a ram. By contrast, pultrusion pulls the fibers, with their coating of matrix material, through the mould or die in which curing or polymerisation takes place. This operation enables the fibers to maintain their pre-stressing in the finished tube. The fibers are always held in this orientation and there is no subsequent loss of the pre-tension when the finished tube is ultimately cut to length.

[0031] It will be understood by a person skilled in the art that carbon fibers are based on a single carbon chain and that there are considerable advantages in terms of tensile strength in using a carbon fiber composite material in which the carbon fibers are aligned according to their original orientation. Also, the pre-stressing that is applied to the fibers during the pultrusion step is maintained during cure of the resin matrix material so that subsequent cutting to length does not affect the tensile properties of the tube material.

[0032] It is also possible, by appropriate disposition and rotation of feed spools, to pultrude a carbon fiber composite tube having additional windings oriented at an angle to the longitudinal axis of the tube. Typically, such windings may be oriented at ±45°. These help to increase the torsional strength of the tube in the finished golf club shaft, which is important for a tube that will be subject to torsional forces when the club head strikes a ball during play. Preferably, the external ±45° windings (or whatever orientation is selected to suit the end use) have an outer covering of pultruded lateral fibers that are, like the innermost fibers, parallel to the longitudinal axis of the finished tube.

[0033] Such tubes can be continuously formed in long lengths that are ultimately cut to size for end use. Thus, a set of golf clubs could be assembled using a single long tube as a source, cut into pieces of appropriate size, according to club length. For example, the longest iron in a set of golf clubs is designated as the 1 iron and has a relatively long upper tube and a relatively long lower tube compared to upper and lower tube lengths in the shorter irons. Nevertheless, the upper and lower tubes of the 1 iron could be sections cut from the same parent upper and lower tubes that are used to cut sections for the 2 iron, the 3 iron and so on, right through the entire set of golf clubs.

[0034] Extensive tests—both robotic and human—indicate that frequency curves and playing characteristics are significantly enhanced by the use of parallel sided tubes. They are superior to the performances of conventional tapered shafts constructed of graphite or steel.

[0035] With the parallel tube type of shaft construction a perfectly consistent range of flexes is produced throughout a set of clubs. This is achieved by adjusting the lengths of thick and thin tubes in relation to the type of club being constructed. For example the “frequency”, expressed in cycles per minute (cpm) can be perfectly controlled from 292 cpm for a number 2 iron through to 328 cpm for a sand wedge. This produces virtually perfect and consistent flexes throughout a set made of graphite. Such consistency was previously impossible. This in turn leads to increased distance—up to 15 yards on every iron club—and improved accuracy, i.e. straighter hitting.

[0036] The terms “frequency” and “frequency matching” will be well understood by persons skilled in the art. The frequency is a measure of a club's rigidity and the term frequency matching is used to describe the even vibration of each club in a set.

[0037] The preferred manufacturing methods and golf clubs enable perfect frequency matching of individual clubs within a set because of the parallel tube shaft design and the method of construction.

[0038] Thus, the preferred golf club shafts include parallel-sided tubes of titanium alloy or a pre-stressed carbon fiber composite material. In the carbon fiber variant, or variants including at least one length of parallel-sided pre-stressed carbon fiber reinforced composite material, the fiber orientation is such that the loads and stresses are transmitted along the co-axial tubular array via the carbon fiber reinforcements, thereby avoiding concentration of stress at traditionally vulnerable positions. The loads and stresses are dissipated evenly and efficiently throughout the shaft, thereby minimizing the risk of breakage.

[0039] Moreover, this efficient transfer of energy allows greater impact force to be imparted to a golf ball during execution of a golf stroke, from the player's hands and arms to the club head, via the shaft.

[0040] Preferably, the polymeric matrix material is a thermosettable material, such as an epoxy resin or a vinyl ester resin.

[0041] The connections between adjoining lengths of tube may be strengthened with a ferrule of, for example, titanium or titanium alloy. In embodiments comprised entirely of parallel-sided pre-stressed carbon fiber reinforced composite tubing, or variants including at least one length of such tubing, the ferrule may be embedded in the fiber layers.

[0042] As described above, a length of parallel-sided tube constructed from titanium alloy may be used as the lowermost tube in the golf club shaft.

[0043] Furthermore, the same alloy may also be used for the other tube or tubes in the shaft. The construction of parallel-sided titanium tubes is less expensive and more consistent than swaging or forging tapered tubes, and they have the same benefits as the tubes constructed from extruded carbon fiber material described elsewhere in this specification. Moreover, many of the difficulties associated with processing titanium are eliminated by such a simplified construction, hence contributing to the affordability of the finished product.

[0044] A preferred arrangement is a hybrid construction in which the lowermost tube is formed of a parallel-sided titanium alloy tube and the uppermost tube is formed of a parallel-sided tube of pre-stressed carbon fiber composite material. Such an arrangement is thought to provide the optimum distribution of weight, since the butt end of the shaft is light in weight, whilst the tip end nearest the club head is relatively more heavy. A further advantage of this preferred arrangement is that the lowermost tube is less susceptible to minor variations in its structural homogeneity, at the very point where stress concentration might occur.

[0045] Just as a ferrule may be used for strengthening purposes between adjoining lengths of tube, so a ferrule may also be used at the tip of the golf club shaft where it is joined to the club head. Where the lowermost tube is formed of extruded carbon fiber material, the ferrule may overlap or partially encase the fiber ends to protect them from accidental impact or abrasion leading to fiber breakage. In the case in which the lowermost tube is formed of titanium alloy, the ferrule may be omitted and the lowermost tube may be considered as an elongated ferrule extending to the first intermediate tube joint above the golf club head.

[0046] As described above in relation to the prior art, the point of attachment of a golf club shaft to the club head is widely recognized as a point of weakness since stresses are concentrated here. However, in a construction according to the preferred manufacturing methods and golf clubs, the stressing forces are transmitted away from this potential area of weakness, so risk of shaft breakage is considerably reduced.

MORE DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Referring now to FIGS. 1 to 4, a golf club 10 is shown consisting essentially of a shaft 20 and a head 50. The shaft 20 is of a modular construction and consists of a pair of parallel-sided tubes 21 and 22 of different diameters arranged co-axially, with a portion of the smaller diameter tube 21 received in the bore of the larger diameter tube 22. The smaller diameter tube 21 forms the lowermost portion of the shaft 20 and is reinforced at its lower end by a titanium ferrule 23 where the shaft is joined to the club head 50. The larger diameter tube 22 forms the upper part of the shaft 20 and is provided at its upper end with a grip portion 24. An intermediate ferrule 25 is provided at the lower extremity of tube 22 to protect the end thereof for reasons which will be explained in more detail below.

[0048] FIG. 2 shows the construction of the tubes 21 and 22, in particular the arrangement of carbon fiber reinforcement. The main constructional feature of the tubes is a layer 26 of straight, pre-stressed and tensioned carbon fibers embedded in a matrix of curable plastics material. The layer 26 is overwound by more carbon fibers 27 oriented at approximately ±45° relative to the longitudinal axis of the tube. The fibers in the overlayer 27 are also under tension.

[0049] FIG. 3 is a part cross-sectional view showing a stabilizing joint between the two tubes 21 and 22 and an intermediate ferrule 25 at the base of larger diameter tube 22. The purpose of the intermediate ferrule 25 is to provide protection to the fiber ends which would otherwise be exposed at the lower extremity of the tube 22. The upper end of tube 21 is received within the bore of tube 22 and the two tubes overlap by an amount “L” which is at least as great as 4 times the internal diameter “D” (FIG. 6) of tube 22. This degree of overlap ensures that the joint is stable and that flexure of the modular shaft does not result in separation of its component tubes. The outer surface of tube 21 is bonded to the inner surface of tube 22 in the region of overlap. An adhesive such as an epoxy resin is used to bond the outer surface of tube 21 to the inner surface of tube 22. FIG. 4 is a part cross-sectional view showing a reinforcing ferrule 23 at the tip of the shaft 20 where it is joined to the club head 50. The ferrule 23 is a titanium tube and may be welded to formations provided within the club head 50 for ensured rigidity. The bore of ferrule 23 is adapted to receive the lower end of tube 21 and protects the exposed fiber ends thereof from accidental damage.

[0050] The parameters for the tensile modulus measured using “Impregnated Strand Test-SACMA Methodology” are between 35 GPa ranging through 40 GPa, to 55 GPa up to a maximum of 64 GPa. The resulting carbon fiber composite, impregnated with epoxy resin or vinyl ester resin as a matrix typically contains 65%, but possibly up to 75%, by volume of fiber in proportion to resin content. It is designed to produce an upper tube of a stiffness measured in a vibration frequency of between 900 and 1000 cycles per minute, measured on a one meter length sample. The lower tube requires a vibration frequency of between 500 and 600 cycles per minute, also measured on a one meter length sample. The higher modulus materials give the optimum frequency at a lighter weight due to less material being required.

[0051] Lighter weight is desirable in the upper or larger tube to compensate for greater weight in the lower and thinner tube, which is helpful in assisting the pendulum effect when swinging the complete club, without increasing overall weight.

[0052] It will be understood by persons skilled in the art that the above-quoted vibration frequency values apply to the shaft alone and that lower frequency values are obtained for an assembled golf club which includes a relatively massive club head portion. The frequency values given in the earlier discussion of “frequency matching” relate to the assembled golf club complete with club head. By contrast, the frequency values given in the preceding paragraph are “specific” frequencies expressed in relation to a finite tube length of one meter. The two frequency rages, though different, are entirely consistent with one another.

[0053] When titanium alloy is employed in the shaft material, the vibration frequency is within the range given above for the carbon fiber variant, but at the lower end of the scale due to the lower modulus of elasticity of titanium compared to carbon fiber composite. Experiments have shown that the best alloy of titanium for this application is titanium containing 3% aluminum and 2.5% vanadium commonly denoted Ti-3-2.5. Typical wall thicknesses range from 0.48 mm to 0.89 mm, with 0.48 mm being the lightest and most flexible suitable for ladies and slow swinging players. At the other end of the scale, 0.89 mm thick tubing is better suited to professional and hard hitting players.

[0054] All the alloys are preferably work hardened and heat treated to provide optimum and consistent flex, surface hardness and torsional strength suitable for lasting qualities required in a golf club shaft.

[0055] Therefore, in a variant of the above-described embodiment, at least the lowermost tube 21 may be substituted by a parallel-sided tube of titanium alloy. As described, the alloy may be a commercially-available aerospace alloy commonly designated as Ti-3-2.5. This alloy has a titanium metal base and contains as its major alloying constituents roughly 3% by weight of aluminum and 2.5% by weight of vanadium. The other tubes in the shaft may also be substituted by such parallel-sided titanium alloy tubes.

[0056] Although FIGS. 1, 3 and 4 have not been drawn to represent a titanium alloy-shafted golf club in particular, persons skilled in the art will appreciate that the tubes illustrated in these Figs. could equally well be made from titanium alloy. Their parallel-sided construction, nested arrangement and method of jointing are the same as described above for the pre-stressed carbon fiber composite variant.

[0057] Conventional golfclub shafts have an overall tapered outline. As a result of this, the golfclub manufacturing industry has become accustomed to providing golf club grips that are adapted to fit over a tapered club shaft. However, the preferred manufacturing methods and golf clubs provide a golf club shaft that has a parallel-sided upper portion. Therefore, in order to make the preferred golf clubs compatible with conventional golf club grips, a tapered sleeve may be applied to the upper butt section to alter its external profile so that a conventional grip can be applied. One such sleeve is illustrated in cross-sectional view in FIG. 5, denoted by reference numeral 60. Preferably, the sleeve 60 is a foam moulded sleeve which has the advantage of imparting a shock-absorbing effect to cushion the player's wrists from any shock experienced at impact when the club head strikes the ball. A golf shot that is played incorrectly can result in a shudder passing through the golf club shaft to the player's wrists through the grip portion. Any cushioning or shock-absorbing effect that the sleeve 60 can provide in these circumstances will contribute to a lowering of player fatigue.

[0058] In a preferred golf club, the golf club shaft is formed from two parallel-sided tubes. The lower tube is connectable to a golf club head in use, and the upper tube is connectable to a golf club grip in use. The lower tube is preferably formed of titanium metal or an alloy thereof containing 3% aluminium and 2.5% vanadium. The upper tube is preferably formed of a composite material of carbon fibers embedded in a matrix of epoxy resin. An inner ply of fibers is oriented parallel to the longitudinal axis of the tube. This is surrounded by outer plies having an orientation of approximately ±45° relative to the longitudinal axis of the tube. Preferably, the ±45° plies have an outer ply of fibers aligned with the inner ply, i.e. parallel to the longitudinal axis of the tube. The upper tube is preferably formed in a pultrusion process as described above, in which the fibers are pulled through a mould or die while the matrix resin is cured.

[0059] Thus, the exemplary golf clubs may be manufactured in high volume at relatively affordable prices.

[0060] The exemplary golf clubs contribute to improved performance on the part of a user without contravening the rules of the game.

[0061] The exemplary golf clubs are capable of enduring the repeated stresses that are experienced during impact with a golf ball by reducing the risk of breakage at conventional stress concentration points.

[0062] The exemplary manufacturing methods provide a golf club that has highly controllable flexibility, thereby enabling a set of clubs to be constructed having matching flexibilites throughout.

[0063] Although the invention has been particularly described above with reference to specific embodiments, it will be understood by persons skilled in the art that these are merely illustrative and that variations are possible without departing from the scope of the claims which follow.

[0064] Benefits, other advantages, and solutions have been described above with regard to specific examples. The described benefits, advantages, solutions, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not critical, required, or essential feature or element of the invention.

[0065] Additional advantages and modifications will readily occur to those skilled in the art. The invention in its broader aspects is not limited to the specific details, representative apparatus, and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the spirit or the scope of Applicants' general inventive concept. The invention is defined in the following claims.