TWO-PIECE GOLF SHAFT

BACKGROUND

Certain multi-piece hybrid golf shafts have been in existence for many years in the golf shaft industry. Examples of existing hybrid golf shafts are described, for example, in U.S Pat. Nos. 6,729,970 and 6,203,447.

SUMMARY

Various embodiments of the present invention provide a two-piece composite golf shaft comprising a hollow upper section and a hollow or solid tip section formed from a chopped carbon fiber/thermoplastic resin material. In some embodiments, the upper section and tip section may be coupled together using an attachment method and device according to embodiments of the present invention, which couples the two pieces together to form a single shaft. This new golf shaft construction and design is applicable to all the different categories associated with a golf club, including, but not limited to, putter shafts, driver shafts, and iron shafts. The lower section (tip section) comprises a chopped carbon fiber/thermoplastic resin material that can be molded into unlimited shapes and sizes and can be solid or hollow in its construction. The chopped carbon fiber/thermoplastic material provides isotropic mechanical properties similar to metals and at the same time overcomes the existing geometry limitations of current steel and carbon/epoxy shafts. The ability to form different geometric cross sections with this chopped carbon fiber/thermoplastic material can allow for increased strength and stiffness compared to traditional round cross-sectional shapes associated with current steel and carbon/epoxy golf shafts. In addition to being able to mold unlimited shapes and contours, this new technology allows for different densities that can be molded and even allows for a gradient of density throughout the tip section. All of these attributes, combined with excellent damping properties, can provide the golfer with a more stable shaft that has a unique feel compared to traditional steel and carbon/epoxy hybrid golf shafts.

In some embodiments, the invention provides a hybrid two-piece golf club shaft comprising an upper tubular shaft section fabricated from carbon fiber composite material which is joined to a lower shaft section utilizing a coupling insert according to embodiments of the present invention. The coupling insert creates a joint wherein the axial straightness is maintained between the upper and lower section and the resulting strength of the bond joint is dramatically increased (e.g., due to mechanical interlocking features of the bond joint geometry).

In some embodiments, the upper shaft section is comprised of carbon fiber/epoxy composite materials to form a tubular structure.

In some embodiments, the upper shaft section has a defined longitudinal axis configured to be aligned to the lower tip section of the shaft.

In some embodiments, the upper shaft section has a defined parallel length section along the longitudinal axis that that is located on the inner diameter of the shaft and is located in the bond joint area.

In some embodiments, the upper shaft section has a circular cross-sectional shape in the radial direction extending throughout the longitudinal axis of the upper shaft section.

In some embodiments, the lower shaft section is comprised of a combination of short chopped carbon fiber and a thermoplastic resin which is then injection molded into the lower tip section.

In some embodiments, the lower shaft section is non-tubular (solid).

In some embodiments, the lower shaft section has a clearly defined longitudinal axis that is aligned to the longitudinal axis of the upper shaft section.

In some embodiments, the lower shaft section contains four semicircular ridges located at equal distance around the circumference of the bond joint end of the lower section.

In some embodiments, the lower shaft section contains four semicircular ridges located at equal distance around the circumference of the bond joint end of the lower section that are convex shaped and slide into a corresponding set of matching concave grooves located within the coupling insert.

In some embodiments, the lower shaft section contains four semicircular ridges located at equal distance around the circumference of the head bond end that is bonded into the golf club head.

In some embodiments, the coupling insert that bonds the upper and lower sections is made of aluminum.

In some embodiments, the coupling insert that bonds the upper and lower sections is made of a carbon fiber/thermoplastic resin material (e.g., KyronMAX).

In some embodiments, the coupling insert that bonds the upper and lower sections is made of stainless steel.

In some embodiments, the coupling insert that bonds the upper and lower sections is made of metal matrix composite.

In some embodiments, the coupling insert incorporates an indexing mark locater which aligns the lower shaft longitudinal axis to the upper shaft longitudinal axis.

In some embodiments, the coupling insert contains a flange section that bridges between the lower and upper section that is visible after bonding.

In some embodiments, the coupling insert contains four semicircular concave grooves that extend on the inside diameter the full length of the coupling insert which accepts the four corresponding convex ridges contained on the bond joint end of the lower tip section.

In some embodiments, the coupling insert has a shoulder on both ends that is slightly smaller (e.g., 0.0005 inches smaller) than the internal diameter of the upper shaft. This close to interference fit properly aligns the coupling insert to the centerline axis of the upper shaft and provides for perfect axial straightness between the upper and lower shaft sections.

In some embodiments, the coupling insert has a knurled surface so that the adhesive has a uniform bondline thickness.

In some embodiments, the lower shaft section is molded into a radial cross-sectional shape that is circular throughout the length of the lower tip section.

In some embodiments, the lower shaft section is molded into a radial cross-sectional shape that is hexagonal throughout the length of the lower tip section.

In some embodiments, the lower shaft section is molded into a radial cross-sectional shape that is octagonal throughout the length of the lower tip section.

In some embodiments, the lower shaft section is molded into a radial cross-sectional shape that is fluted with six recessed channels throughout the length of the lower tip section.

In some embodiments, the lower shaft section is molded into a radial cross-sectional shape that is tapered throughout the length of the lower tip section, thus increasing in diameter at the head bond end and increasing in diameter up to the bond joint end of the lower tip section.

In some embodiments, the lower shaft section is molded into a non-linear longitudinal shape with a variety of axes.

In some embodiments, the lower shaft section is molded into a non-linear longitudinal shape with a double bend or single bend shape required for putter shafts.

In some embodiments, the lower tip section can have the density of the carbon fiber/thermoplastic resin modified to change the overall density of the lower tip section.

In some embodiments, the lower shaft section can have a density ranging from 1.2 grams/cubic centimeter up to 10 grams/cubic centimeter.

In some embodiments, the lower shaft section can have a density that varies from a higher density at the head bond end of the lower tip section and reducing in density moving towards the opposite end of the lower tip section.

In some embodiments, the lower tip section can be inserted into a traditional bore hole contained in all golf club heads.

In some embodiments, the lower shaft section has a hole drilled in the center of the lower tip section that will slide over a head design that incorporates a solid post design instead a round bore hole.

In some embodiments, the invention provides a set of golf clubs each golf club in the set containing a two-piece golf club shaft as described above having a descending length of the lower tip section as the club length gets shorter throughout the set of clubs.

In some embodiments, the invention provides a set of golf clubs each golf club in the set containing a two-piece golf club shaft as described above having an ascending length of the lower tip section as the club length gets shorter throughout the set of clubs.

In some embodiments, the invention provides a set of golf clubs each golf club in the set containing a two-piece golf club shaft as described above having a constant length of the lower tip section as the club length gets shorter throughout the set of clubs.

In some embodiments, the lower shaft section is tubular in nature, with an outer diameter that matches the inner diameter of the upper section of the golf shaft allowing it to be installed directly into the upper section by simply bonding the lower section into the upper section. In some embodiments a universal coupler comprising machined aluminum, titanium, or steel, or an injection-molded composite material, could be used that fits internally and externally on the upper and lower sections of the golf shaft, respectively.

In some embodiments, the invention provides a two-piece golf shaft, comprising a hollow upper section; a hollow or solid lower section; and a coupling insert configured to join the upper section and the lower section together, wherein the lower section is formed from an injection-molded carbon fiber-reinforced thermoplastic material, and wherein the coupling insert comprises a hollow structure configured to fit into an inner diameter of the upper section and configured to receive an end of the lower section inserted therein.

In some embodiments, the carbon-reinforced thermoplastic material comprises short length chopped carbon fiber and thermoplastic resin.

In some embodiments, the carbon-reinforced thermoplastic material comprises about 30% to about 50% chopped carbon fiber.

In some embodiments, the carbon-reinforced thermoplastic material comprises a polyamide thermoplastic resin or derivative thereof

In some embodiments, at least one end of the lower section has an exterior surface configured to mate with an interior surface of the coupling insert.

In some embodiments, the exterior surface of at least one end of the lower section and at least a portion of the interior surface of the coupling insert are smooth.

In some embodiments, the exterior surface of at least one end of the lower section comprises a plurality of convex ridges configured to mate with a plurality of concave grooves on the interior surface of the coupling insert.

In some embodiments, the coupling insert is formed from a machined metal or alloy.

In some embodiments, the coupling insert comprises aluminum, titanium, or stainless steel.

In some embodiments, the coupling insert is formed from an injection-molded carbon fiber-reinforced thermoplastic material or metal mesh composite material.

In some embodiments, the coupling insert includes a flange or head portion on one end, the flange or head portion configured to form a bridge that is visible between the upper section and the lower section after they are joined together.

In some embodiments, the coupling insert has an exterior surface comprising at least one shoulder configured to provide an interference fit with the inner diameter of the upper section.

In some embodiments, the coupling insert has an exterior surface comprising a knurled surface on at least a portion thereof.

In some embodiments, the lower section has a cross-sectional shape that is circular, hexagonal, octagonal, or fluted.

In some embodiments, the lower section is hollow.

In some embodiments, the lower section is tapered, decreasing in diameter from a proximal end toward a distal end thereof.

In some embodiments, the lower section is molded into a non-linear shape with a variety of longitudinal axes.

In some embodiments, the lower section has a density ranging from about 1.2 grams/cubic centimeter to about 10 grams/cubic centimeter.

In some embodiments, the lower section has a density gradient, whereby the density increases from a proximal end toward a distal end thereof.

In some embodiments, the lower section includes a metal mesh or rod.

Additional features and advantages of embodiments of the present invention are described further below. This summary section is meant merely to illustrate certain features of embodiments of the invention, and is not meant to limit the scope of the invention in any way. The failure to discuss a specific feature or embodiment of the invention, or the inclusion of one or more features in this summary section, should not be construed to limit the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description of certain embodiments of the application, will be better understood when read in conjunction with the appended drawings. For the purposes of illustrating the systems and methods of the present application, there are shown in the drawings preferred embodiments. It should be understood, however, that the application is not limited to the precise arrangements and instrumentalities shown. In the drawings:

FIG. 1 is a perspective view of an illustrative golf club (putter), including a putter head, a grip, and a two-piece shaft according to various embodiments of the present invention;

FIG. 2 is a perspective view of an illustrative golf club (iron), including an iron head, a grip, and a two-piece shaft according to various embodiments of the present invention;

FIG. 3 is a perspective view of an illustrative golf club (driver), including a driver head, a grip, and a two-piece shaft according to various embodiments of the present invention;

FIG. 4A is an exploded view of a putter shaft according to various embodiments of the present invention, configured to be bonded into a female opening on the putter head; FIG. 4B is an exploded view of a putter shaft according to various embodiments of the present invention, configured to be bonded into a female opening on the putter head;

FIG. 5 is an exploded view of a putter shaft according to various embodiments of the present invention, configured to be bonded into a female opening on the putter head utilizing a second coupler insert;

FIG. 6 is an exploded view of a putter shaft according to various embodiments of the present invention, configured to be bonded over a cylindrical metallic post on the putter head utilizing a second coupler insert;

FIG. 7 is an exploded view of a putter shaft according to various embodiments of the present invention, configured to be bonded over a cylindrical metallic post on the putter head;

FIG. 8A is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, configured to be bonded to both the upper section of the hollow shaft and the putter head itself with a female bond joint;

FIG. 8B is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 8C is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 8D is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 9A is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, configured to be bonded to both the upper section of the hollow shaft and the putter head itself with an over post bond joint;

FIG. 9B is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 10A is a cross-sectional view of the center of the longitudinal axis of the tip section of FIG. 9A, which has a circular geometry that is tapered from the large end to the smaller end;

FIG. 10B is a cross-sectional view of the center of the longitudinal axis of the tip section of FIG. 9B, which has a circular geometry that is tapered from the large end to the smaller end;

FIG. 11A is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, configured to be bonded to both the upper section of the hollow shaft and the putter head itself with a female bond joint;

FIG. 11B is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 12A is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, configured to be bonded to both the upper section of the hollow shaft and the putter head itself with an over post bond joint;

FIG. 12B is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 12C is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 12D is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 13A is a cross-sectional view of the center of the longitudinal axis of the tip section of FIG. 12A, which has a hexagonal geometry consisting of six symmetric flat sides that are tapered from the large end to the smaller end;

FIG. 13B is a cross-sectional view of the center of the longitudinal axis of the tip section of FIG. 12B, which has a hexagonal geometry consisting of six symmetric flat sides that are tapered from the large end to the smaller end;

FIG. 14A is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, configured to be bonded to both the upper section of the hollow shaft and the putter head itself with an over post bond joint;

FIG. 14B is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 14C is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 14D is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 15A is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, configured to be bonded to both the upper section of the hollow shaft and the putter head itself with a female bond joint;

FIG. 15B is a detail view of a tip section of a putter shaft according to various embodiments of the present invention;

FIG. 16A is a cross-sectional view of the center of the longitudinal axis of the tip section of FIG. 15A, which has a fluted geometry consisting of six semicircular flutes that are tapered from the large end to the smaller end;

FIG. 16B is a cross-sectional view of the center of the longitudinal axis of the tip section of FIG. 15B, which has a fluted geometry consisting of six semicircular flutes that are tapered from the large end to the smaller end;

FIG. 17 is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, configured to be bonded to both the upper section of the hollow shaft and the putter head itself with a female bond joint, the longitudinal axis having a double bending geometry;

FIG. 18A is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, configured to be bonded to both the upper section of the hollow shaft and the putter head itself with an over post bond joint, the longitudinal axis having a double bending geometry;

FIG. 18B is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, configured to be bonded to both the upper section of the hollow shaft and the putter head itself with an over post bond joint, the longitudinal axis having a double bending geometry;

FIG. 19 is a cross-sectional view of the center of the longitudinal axis of the tip section of FIG. 18A, which has a circular geometry that is tapered from the large end to the smaller end;

FIG. 20A is a cross-sectional isometric view of a tip section of a putter shaft according to various embodiments of the present invention, which is reinforced with a layer of metal mesh;

FIG. 20B is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, depicting a gradient of density from the head bond joint end to the upper bond joint into the upper shaft section;

FIG. 20C is a detail view of a tip section of a putter shaft according to various embodiments of the present invention, depicting a gradient of density from the head bond joint end to the upper bond joint into the upper shaft section;

FIG. 21 shows three different views of a coupling insert for a two-piece shaft according to various embodiments of the present invention, configured to bond the lower tip section to the upper shaft section;

FIG. 22 is a cross-sectional end view of the coupling insert of FIG. 21, showing the four semicircle channels that the lower section locks and bonds into;

FIG. 23 is a cross-sectional front view of the coupling insert of FIG. 21, showing the four semicircle channels that the lower section locks and bonds into;

FIG. 24 is a cross-sectional view of the reverse geometry of the coupling insert that is contained on one or both ends of the lower tip section of a two-piece shaft according to various embodiments of the present invention, providing a mechanical interlock between the lower and upper section;

FIG. 25 shows five different views of a coupling insert for a two-piece shaft according to various embodiments of the present invention, configured to bond the lower tip section to the upper shaft section;

FIG. 26A is an illustrative array of iron golf clubs forming a set that contains a descending overall shaft length coupled with a descending length of the lower tip section of a two-piece shaft according to various embodiments of the present invention;

FIG. 26B is an exploded view of an iron shaft according to various embodiments of the present invention;

FIG. 27A is an illustrative array of driver golf clubs forming a set that contains a descending overall shaft length coupled with a descending length of the lower tip section of a two-piece shaft according to various embodiments of the present invention; and

FIG. 27B is an exploded view of a driver shaft according to various embodiments of the present invention.

DETAILED DESCRIPTION

As noted above, certain multi-piece hybrid golf shafts have been in existence for many years in the golf shaft industry. Examples of existing hybrid composite/metal golf shafts are described, for example, in U.S. Pat. Nos. 6,729,970 and 6,203,447. The shafts described in those patents rely on bonding a steel tip section that is hollow, to a composite upper section shaft that is also hollow. The two sections are bonded together using a coupling ferrule that is adhesively bonded to the internal diameters of both the upper and lower sections. The ferrules are constructed using a carbon/epoxy composite material that is glued into both ends of the steel tip section and the composite upper section. The prior art ferrules are very simplistic in their design and only provide for coupling the two different sections together. They do not provide for any mechanical indexing between the upper section and the lower section. Furthermore, in most cases the ferrule is bonded into the upper section of the composite shaft that has very thin wall thicknesses which causes a weak point in the overall shaft and is prone to failure at the joint intersection.

The theory behind using a steel tip hollow section in the tip of hybrid two-piece shafts is that steel provides for very low torque values and has a density that is four to five times that of carbon/epoxy material. The lower torque values improve the performance of the overall club by minimizing the twisting of the shaft especially in off center ball strike locations. The heavier density located near the head, increases the mass distribution of the overall club by shifting the center of gravity towards the golf club head. This also helps in terms of counterbalancing the overall club. The other reason that steel has been used in hybrid golf shafts is for putter shaft applications that require the tip section of the shaft to have complex bend geometries for different types of putter head offsets. Steel is relatively easy to form and bend to some of the complex geometries, whereas graphite shafts are very restricted in terms of complex bend geometries. This is due to some of the process limitations of carbon tubular structures and the costs associated with manufacturing carbon/epoxy golf shafts with complex shapes.

The current hybrid golf shafts in the market today have been limited to circular longitudinal cross-sectional geometries formed from steel. Apart from the benefit of being able to form a hollow steel tip section of existing hybrid composite/steel golf shafts into complex bend geometries, steel has significant limitations in wall thickness and formability to form into alternate cross-sectional shapes. A circular cross section in hollow steel shafts is a common shape; however, forming a steel golf shaft into longitudinal cross-sectional shapes like a hexagon, octagon, fluted, etc. is extremely challenging since these parts are tapered and very thin-walled structures. The result in trying to form hollow steel golf shafts or steel tip sections of golf shafts into complex cross-sectional shapes can cause metal fatigue, cracking and generally structurally weak designs.

As mentioned in U.S. Pat. No. 6,203,447, prior art hybrid modular golf shafts that have a steel segment and a composite segment are prone to galvanic corrosion in the area where the two shafts are joined when in the presence of moisture, especially high salinity moisture commonly found near golf courses near a salt water source. This type of corrosion can not only cause a visible outward area of corrosion, but also significantly weaken the bond joint area. Prior methods to overcome this scenario have utilized placing glass beads in the epoxy bond joint to minimize contact between the steel portion of the golf shaft and the composite segment in addition to using a plastic ferrule that is nonconductive.

The present invention provides, in various embodiments, a hybrid two-piece golf shaft that can overcome the above-described deficiencies, and can provide, for example, for a variety of cross-sectional geometries, a variety of longitudinal axis profiles, an increase in strength, and/or a lowering of torque values in the tip section, as compared to existing products in the art. In various embodiments of the present invention, the lower section of the two-piece shaft can be accurately bonded to the upper section via a coupling insert that can provide for essentially perfect alignment between the two sections, can reduce/eliminate the galvanic corrosion scenario described above, and/or can position the shaft in the desired location within the head itself.

Various embodiments of the present invention provide for a lightweight hybrid composite/thermoplastic tip golf shaft construction for a variety of various golf club types. The types of golf clubs where the present invention is applicable include drivers, irons, and putters.

In some embodiments, the present invention includes a hybrid shaft construction comprising a hollow (tubular) composite shaft upper section, and a lower section that is made from a chopped carbon fiber/thermoplastic resin material (solid or hollow), the two sections coupled together with a coupling insert according to embodiments of the present invention.

The upper composite shaft section may be manufactured similar to existing full-length one-piece golf shafts and may utilize similar materials to the current art (such as, but not limited to, traditional carbon fiber sheets or the metal mesh composite materials described in U.S. patent application Ser. No. 17/165,721, which is incorporated by reference herein in its entirety). The outer diameters and inner diameters along with the lengths of the composite upper section can vary depending on the end use application of the golf club. In essence, a composite upper section of an iron shaft, for example, will inherently be longer in length compared to an upper section of a putter shaft given the overall lengths of the two different clubs. In some embodiments, the upper section shaft outer diameter where the shaft meets up with the lower section may have the same outer diameter of the adjoining lower tip section when it is bonded together yielding a uniform bond joint between the lower and upper section. However, in other embodiments, the lower section outer diameter could be larger or smaller in diameter compared to the outer diameter of the upper section where the joint occurs.

In some embodiments, the upper composite tubular shaft segment may contain a parallel internal diameter (e.g., for a minimum of about two inches) that is located in the bond joint end of the upper section. This provides a uniform region for the coupling insert to be adhesively bonded into. This parallel section can allow the coupling insert to seat properly which can help in maintaining the lower section alignment.

In some embodiments, the upper composite shaft section is a lightweight composite shaft which helps add to the counterbalance properties of the overall club in addition to reducing the overall weight of the golf club thus increasing the swing speed of the club equating to increased distance especially in driver clubs.

In some embodiments, the lower tip section of the shaft is made from a combination of blending short length chopped carbon fiber with a thermoplastic resin (such as, but not limited to, the KyronMAX compounds provided by Mitsubishi Chemical Advanced Materials). This composite thermoplastic segment of the two-piece hybrid construction can be manufactured via an injection molding process commonly used to fabricate many plastic parts. In some embodiments, the preferred plastic is polyamide and derivatives of polyamide thermoplastic resin. Polyamide has a favorable blend of mechanical properties and surface finish for this application. However, there are many other types of plastic materials that can be used in other embodiments, including, but not limited to: polyimide polycarbonate, nylon, polypropylene, etc. An important feature of this material technology is the process involved with the accurate blending of the carbon fiber reinforcement and the plastic resin prior to the combined material going through the injection molding process. In certain preferred embodiments, the fiber volume to resin ratio is approximately 30% carbon and 70% thermoplastic resin. In other embodiments, the ratio of carbon fiber to thermoplastic resin can be increased to as high as 50% if desired; however, increasing the fiber ratio to this level can create a surface finish that is not desirable and difficult to paint. Therefore, in some embodiments, the preferred fiber to resin ratio is about 30% carbon. Even at a 30% fiber ratio, this material can achieve virtual isotropic properties that are similar to 7075 T6 aluminum. Unlike continuous carbon fiber/epoxy structures that are extremely anisotropic in nature, the chopped carbon fiber/thermoplastic resin material (e.g., KyronMAX) used in embodiments of the present invention exhibits the same properties in all directions.

In various embodiments of the present invention, due to the nature of an injection molding process, as well as the chopped carbon/thermoplastic material, it is possible to mold not just a simple circular shaped cross section in the tip section, but virtually any cross-sectional shape desired. This is very hard and costly to achieve with continuous reinforced carbon/epoxy materials in addition to steel. As shown in the drawings (described further below), a variety of cross-sectional shapes may be used in this application. These shapes include, but are not limited to, hexagonal, fluted, and octagonal shapes among others. All of these shapes may include a tapering section from large to small extending from the bond joint end towards the extreme tip of the overall golf shaft. Trying to achieve a complex geometry while at the same time adding in a taper increases the complexity in the manufacturing of these shapes substantially. Trying to achieve these types of shapes utilizing steel golf shaft construction techniques or continuous carbon fiber/epoxy golf shaft construction techniques would be extremely difficult, costly, and prone to mechanical failure. One of the main benefits of an injection molding process according to embodiments of the present invention, is that the processing techniques yield a low cost, extremely consistent part with all the benefits of a thermoplastic material.

Utilizing an injection molding process with a chopped carbon fiber/thermoplastic material as described herein not only allows for different cross-sectional shapes as mentioned above, but it allows for different longitudinal geometries beyond just manufacturing a straight tip section. This is especially pertinent when one looks at the different putter shaft shapes that are within the current art. Many putters are designed to have what is called an offset between the neutral axis of the golf shaft and the location of the putter head. This can be seen with double and single bend putter shaft on the market today. The offset helps golfers align the putter head in a different fashion than a straight shafted putter. The key point is, that manufacturing a straight tapered tip cross section with different cross-sectional shapes is a difficult and cost prohibitive process when utilizing continuous carbon fiber/epoxy or steel materials. Now couple this with then adding another axis change like a double bend putter shape, and the process becomes unviable unless an injection mold or compression mold process is utilized. In an alternate embodiment, one could use a sheet molding compound (SMC) with a compression molding process to achieve similar types of complex geometries. However, using an SMC does not achieve the same isotropic nor damping properties that can be achieved with chopped carbon fiber/thermoplastic materials.

A further benefit of embodiments of the present invention with respect to the chopped carbon fiber/thermoplastic resin material is the strength of the tip. Unlike tubular steel and composite shafts used in existing hybrid two-piece golf shafts, embodiments of the present invention may have a hollow or solid tip section comprised of 100% chopped carbon fiber/thermoplastic material. The chopped carbon fiber/thermoplastic tip section can provide, for example, for increased strength, increased mass, and/or increased stiffness and stability compared to tubular steel structures. This is especially true when adding different geometric cross-sectional shapes like a fluted or hexagonal shape.

Still another benefit of various embodiments of the present invention, is that the ends of the lower tip section itself may have a geometric design that provides for a mechanical locking joint into a coupling insert according to embodiments of the invention, which may be bonded, for example, to the inside of the upper shaft section. Thermoplastic materials in general can be difficult to adhesively bond together to like materials or even dissimilar materials by relying on just the adhesive to provide sufficient bond strength. Therefore, shafts according to various embodiments of the present invention do not solely rely on adhesive providing the necessary bond strength required for the bond joint, but may also include a mechanical interlock that can help eliminate the possibility of the lower shaft section debonding from the coupler insert and the upper section. In certain preferred embodiments, four equal distant semicircular concave features are placed at the end which is bonded into the coupling insert. Once pressed in and cured along with the use of an adhesive material, the ability to debond and fail in the joint area under normal playing conditions is virtually eliminated. This construction can also aid in the alignment between the lower section and the upper section providing for essentially perfect axial straightness between the upper shaft and the lower tip section. This mechanical alignment can be especially critical when one is aligning a lower section that has a complex axial geometry, like a double bend putter shaft. It is understood that there are numerous potential geometric shapes other than a semicircle that one could use to achieve a mechanical interlock, however this is a preferred design based upon molding difficulty and cost. In some cases, there can be a mechanical interlock not just between the two shaft segments, but also into the head itself using a similar type of coupling insert.

Yet another benefit of utilizing a lower tip construction with chopped carbon fiber/thermoplastic material, is that the density of the resulting combined short chopped carbon fiber and thermoplastic resin can be varied over a wide range. In various embodiments, the net resulting density on the light side may be approximately 1.4 grams/cubic centimeter and can be increased up to approximately 10 grams/cubic centimeter by adding a dense filler material like tungsten to achieve higher densities. As is shown in the drawings, the density can be increased throughout the length of the tip section in a uniform density, or can be varied throughout the length of the tip section generating a denser section at the extreme tip and a lighter density moving up towards the bond joint region. The performance benefit of the overall golf club is to increase the counterbalance properties by shifting more mass towards the club head itself.

A further benefit of utilizing the chopped carbon fiber/thermoplastic material in this application, is that it dampens the modal vibrations that are generated from striking a golf ball that end up transmitting up the shaft into the hands of the golfer. The damping properties along with the aforementioned benefits make this an ideal material for this application.

Another aspect of embodiments of the present invention centers around a coupling insert that joins the lower section to the upper section. As mentioned in prior art examples, commonly used ferrules have been utilized to join the upper and lower segments of hybrid golf shafts. These ferrules are usually constructed from a smaller tubular composite tube that is bonded to the internal diameters of the two sections. The present invention, in various embodiments, provides a coupling insert that may be metallic in design and is first bonded to the upper shaft section and may be located on a specific axis identified by a locator on the shaft itself. This reference locator point is usually the graphics that are applied to the upper section of the composite shaft. In certain preferred embodiments, the coupling insert is made out of machined aluminum or alloy thereof (e.g., 6061, 6062, or 7001 aluminum), but in other embodiments may be injection molded and may comprise carbon fiber reinforced thermoplastic resin (e.g., KyronMAX), other thermoplastic materials, and/or other metals (titanium, stainless steel, etc.) or alloys. As shown in the drawings, the coupling insert can vary in length and diameter based upon where it is bonded into the two shaft segments. This can vary based upon whether the shaft is a driver, iron, or putter shaft. In certain preferred embodiments, the coupler insert is approximately two inches long which is sufficient length to transfer the loads and maintain stiffness in the joint area. In some embodiments, the inside of the coupling insert has four symmetric concave semicircles that match the geometry and size of the bond end of the lower tip section. These four concave semicircles align with the four concave semicircles located on the tip section so that the two pieces mechanically interlock and eliminate any variation in the axial alignment of the two shaft segments. The four concave semicircles located on the lower tip section create a close to interference fit when pressed in, creating an in situ alignment mechanism. In other embodiments, the inside of the coupling insert and the bond end of the lower tip section may be configured for a smooth interference fit. The surrounding bond area is adhesively bonded providing additional strength. The coupling insert has a wider flange or head section on the end which creates a bridge between the upper and lower shaft sections. This coupler insert can be anodized a color to both seal the aluminum and proved for an aesthetically appealing look in the joint area.

Given the above explanation of the key elements of embodiments of the present invention and how they relate to the shaft itself, one can now envision different applications of this invention and how those elements might be applied to a set of irons or a set of drivers including fairway woods. Specifically, within a set of iron shafts or driver and fairway shafts the hybrid shaft lengths can vary along with the individual lengths of both the upper and lower sections. This can create a descending location of the bond joint region or an ascending location of the bond joint region. This can be done to achieve low launch angle to high launch angles by simply changing the location of the bond joint area.

Further configurations and details of various embodiments of the present invention will become apparent in the drawings provided herewith and the detailed descriptions provided below. The following detailed descriptions of the drawings are meant to explain the details of certain preferred embodiments and are not intended to limit the scope of the invention to the described uses. In the embodiments shown in the drawings, the lower tip sections are constructed using a chopped carbon fiber reinforced thermoplastic resin (such as, but not limited to, the KyronMAX compounds provided by Mitsubishi Chemical Advanced Materials); however, in other embodiments, different composite materials (existing or to be developed) may be used, provided they can be injection molded into shaft sections as described herein.

FIG. 1 illustrates a putter club and contains a hybrid shaft 2 of an illustrative embodiment of the invention. The darker area of 2 represents the composite upper section of the shaft and the lighter section at the bottom represents the lower tip section of the hybrid shaft. The putter head 5 is bonded to the lower tip section of the club and the putter grip is represented by 1 that is bonded to the upper section.

FIG. 2 illustrates an iron club and contains a hybrid shaft 3 of an illustrative embodiment of the invention. The darker area of 3 represents the composite upper section of the shaft and the lighter section at the bottom represents the lower tip section of the hybrid shaft, The iron head 6 is bonded to the lower tip section of the club and the putter grip is represented by 1 that is bonded to the upper section.

FIG. 3 illustrates a driver club and contains a hybrid shaft 4 of a preferred embodiment of the invention. The darker area of 4 represents the composite upper section of the shaft and the lighter section at the bottom represents the lower tip section of the hybrid shaft. The driver head 44 is bonded to the lower tip section of the club and the putter grip is represented by 1 that is bonded to the upper section.

FIG. 4A is a schematic view of the key components that make up a hybrid putter shaft according to various embodiments of the invention. The putter head 5 is what is called a “Plumbers Neck” design which simply means that the putter shaft is bonded into a female opening where the tip of the hybrid putter shaft is bonded into. In this scenario depicted, the tip of the shaft 9 is adhesively bonded into the putter head bore hole, and a feature that may function as a means for glue relief 43 is provided. The feature that may function as a means for glue relief may comprise, for example, a hole that is machined into the head end of the solid tip section. In some embodiments, the hole may be relatively shallow (e.g., configured specifically to accommodate for a small amount of excess glue to escape and go up a portion of the tip section); however, in other embodiments the hole may be deeper (e.g., similar to or essentially the same as the hole described and shown herein for “Over Post” designs). In other embodiments, the tip of the shaft 9 for the “Plumbers Neck” design may be smooth (e.g., as in FIG. 8A). The cross section of the hybrid shaft tip section 9 is depicted having a hexagonal cross section in the radial direction. At the joint end of the lower tip section, exists four semicircular concave ridges that slide into the coupler insert 8. The coupler insert is adhesively bonded into the upper shaft section 7 prior to bonding in the lower tip section 9. These three components 7, 8, 9 constitute the hybrid shaft for this configuration.

FIG. 5 is a schematic view of the key components that make up a hybrid putter shaft according to various other embodiments of the invention. The putter head 5 is what is called a “Plumbers Neck” design which simply means that the putter shaft is bonded into a female opening where the tip of the hybrid putter shaft is bonded into. In this scenario depicted, the tip of the shaft 10 is adhesively bonded into the coupler insert 8 which is then bonded into the putter head bore hole. The cross section of the hybrid shaft tip section 10 is depicted having a hexagonal cross section in the radial direction. At the joint end and the head end of the lower tip section, exists four semicircular concave ridges that slide into the coupler inserts 8. The coupler insert 8 at the joint end is adhesively bonded into the upper shaft section 7 prior to bonding in the lower tip section 10. These three components 7, 8, 10 constitute the hybrid shaft for this configuration.

In other embodiments, different hybrid shaft tip sections may be used for the putter shafts, which utilize different cross sections and/or different coupling inserts according to other embodiments of the invention. For example, as shown in FIG. 4B, a hybrid shaft tip section 20 may be used, which may be assembled with putter head 5 and upper shaft section 7 as described above for hybrid shaft tip section 9, but has a circular cross section in the radial direction, and has a smooth joint end that is configured to slide into a coupler insert 24. These three components 7, 24, 20 constitute the hybrid shaft for this configuration.

FIG. 6 is a schematic view of the key components that make up a hybrid putter shaft according to additional embodiments of the invention. The putter head 11 is what is called a “Over Post” design which simply means that the putter shaft is bonded onto a male post extending up from the shank of the putter head 11. In this configuration, the solid tip lower shaft section 12 has a hole machined into the solid tip section that is constructed and arranged to slip over the metal post located at the top of the putter head 11 shank and is adhesively bonded to the coupler insert 8 and to the putter head 11. The cross section of the hybrid shaft tip section 12 is depicted having a hexagonal cross section in the radial direction. At the joint end and at the head end of the lower tip section 12, exists four semicircular concave ridges that slide into the coupler inserts 8. The coupler insert 8 at the joint end is adhesively bonded into the upper shaft section 7 prior to bonding in the lower tip section 12 and then the coupler insert 8 at the head end is adhesively bonded over the steel post of the putter head 11. These three components 7, 8, 12 constitute the hybrid shaft for this configuration.

FIG. 7 is a schematic view of the key components that make up a hybrid putter shaft according to other embodiments of the invention. The putter head 11 is what is called a “Over Post” design which simply means that the putter shaft is bonded onto a male post extending up from the shank of the putter head 11. In this configuration, the solid tip lower shaft section 13 has a hole machined into the solid tip section that is constructed and arranged to slip over the metal post located at the top of the putter head 11 shank and is adhesively bonded to the putter head 11. The cross section of the hybrid shaft tip section 13 is depicted having a hexagonal cross section in the radial direction. At the joint end of the lower tip section 13, exists four semicircular concave ridges that slide into the coupler insert 8. The coupler insert is adhesively bonded into the upper shaft section 7 prior to bonding in the lower tip section 13 and then the head end of the lower tip section 13 is adhesively bonded over the steel post of the putter head 11. These three components 7, 8, 13 constitute the hybrid shaft for this configuration.

FIG. 8A is an isometric view of an illustrative embodiment of a lower tip section 14. In this particular view, the solid tip section contains a joint end 18 with four convex semicircles that slide into the coupler insert 8 which then is bonded into the upper shaft section 7. The head bond end 16 is a smooth surface with the absence of a hole drilled into the tip. This is an example of a bond end designed for a “Plumbers Neck” 5 or female bore into the head itself. In other embodiments, a feature that may function as a means for glue relief may be provided in the “Plumbers Neck” design (e.g., as described above in connection with FIG. 4A), or a head bond end 19 may be provided for an “Over Post” design (e.g., with a hole constructed and arranged to slip over the metal post located at the top of the club head, as in FIG. 12A).

FIG. 9A is an isometric view of another illustrative embodiment of a lower tip section 14. In this particular view, the solid tip section contains a joint end 18 with four convex semicircles that slide into the coupler insert 8 which then is bonded into the upper shaft section 7. The head bond end 17 also is configured with four convex semicircles that will slide into a coupler insert 8 and then is bonded over the head post 11. This is an example of a bond end designed for “Over Post” 11 head designs. In other embodiments, the head bond end 18 may be provided for a “Plumber's Neck” design (e.g., with a smooth end surface as in FIG. 11A).

As will be appreciated by one of skill in the art, lower tip sections with different cross-sectional geometries (circular, hexagonal, fluted, etc.) according to embodiments of the invention can have various combinations of joint end and head bond end. For example, FIG. 8B shows a circular lower tip section 14 with head bond end 16 analogous to FIG. 8A, but with a smooth joint end 15 that is configured to slide into a coupler insert 24. According to various embodiments of the invention, a lower tip section 14, 21, 22 or 23 with a joint end 15 or 18 (for use with a coupling insert 8 or 24) may have a head bond end configured for a “Plumbers Neck” 5 head design (with or without a feature that may function as a means for glue relief) or an “Over Post” 11 head design, and may be configured for use with or without a second coupling insert 8 or 24.

FIG. 10A is a cross-sectional view of the radial geometry of the lower tip section 14 examples according to some embodiments. In this configuration, the radial cross section is solid circular and it is conceived that there are multiple variants possible of the radial cross-section covered for this invention. It is also expected that most if not all of the lower tip sections are tapering from the head bond end and increasing in diameter to the bond joint end where the upper and lower shaft sections are bonded together.

In other illustrative embodiments, as shown for example in FIG. 10B, the lower tip section 14 may be hollow. FIGS. 8C, 8D, and 9B show embodiments analogous to those depicted in FIGS. 8A, 8B, and 9A, respectively, but wherein the lower tip section 14 has a hollow circular cross section in the radial direction (as indicated by the dotted lines).

FIG. 11A is an isometric view of an illustrative embodiment of a lower tip section 21. In this particular view, the solid tip section contains a joint end 18 with four convex semicircles that slide into the coupler insert 8 which then is bonded into the upper shaft section 7. The head bond end 18 also is configured with four convex semicircles that will slide into a coupler insert 8. This is an example of a bond end designed for a “Plumbers Neck” 5 or female bore into the head itself. See, for example, the exploded view of FIG. 5 (where the tip section embodiment of FIG.11A is indicated at numeral 10). If a second coupler insert is not utilized, a head bond end 16 may be provided (e.g., as in FIG. 8A), and either 16 or 18 may be optionally provided with a feature that may function as a means for glue relief (e.g., as described above in connection with FIG. 4A).

FIG. 12A is an isometric view of another illustrative embodiment of a lower tip section 21. In this particular view, the solid tip section contains a joint end 18 with four convex semicircles that slide into the coupler insert 8 which then is bonded into the upper shaft section 7. The head bond end 19 is a smooth surface with a hole drilled in the center that is constructed and arranged to be bonded over the head post 11. This is an example of a bond end designed for “Over Post” 11 head designs. If a second coupler insert 8 is utilized, a head bond end 17 may be provided (e.g., as in FIG. 9A).

As described above, lower tip sections according to embodiments of the invention can have various combinations of cross-sectional geometry, joint end and head bond end. For example, FIG. 12B shows a hexagonal lower tip section 21 with head bond end 19 analogous to FIG. 12A, but with a smooth joint end 15 that is configured to slide into a coupler insert 24.

FIG. 13A is a cross-sectional view of the radial geometry of the lower tip section 21 examples according to some embodiments. In this configuration, the radial cross section is solid hexagonal and it is conceived that there are multiple variants possible of the radial cross-section covered for this invention. It is also expected that most if not all of the lower tip sections are tapering from the head bond end and increasing in diameter to the bond joint end where the upper and lower shaft sections are bonded together.

In other illustrative embodiments, as shown for example in FIG. 13B, the lower tip section 21 may be hollow. FIGS. 11B, 12C, and 12D show embodiments analogous to those depicted in FIGS. 11A, 12A, and 12B, respectively, but wherein the lower tip section 21 has a hollow hexagonal cross section in the radial direction (as indicated by the dotted lines).

FIG. 14A is an isometric view of an illustrative embodiment of a lower tip section 22. In this particular view, the solid tip section contains a joint end 18 with four convex semicircles that slide into the coupler insert 8 which then is bonded into the upper shaft section 7. The head bond end 19 is a smooth surface with a hole drilled in the center that is constructed and arranged to be bonded over the head post 11. This is an example of a bond end designed for “Over Post” 11 head designs. If a second coupler insert 8 is utilized, a head bond end 17 may be provided (e.g., as in FIG. 9A). As shown by the contrast between the darker and lighter areas of this view, the flutes contained within this design are recessed from the outer surface of the lower tip section. These flutes or troughs extend only in the non-bond area and extend from the tip of the lower tip section up to the bond joint region where the two shafts are bonded together.

FIG. 15A is an isometric view of another illustrative embodiment of a lower tip section 22. In this particular view, the solid tip section contains a joint end 18 with four convex semicircles that slide into the coupler insert 8 which then is bonded into the upper shaft section 7. The head bond end 18 also is configured with four convex semicircles that will slide into a coupler insert 8 which is then bonded into the head 5. This is an example of a bond end designed for a “Plumbers Neck” 5 or female bore into the head itself If a second coupler insert is not utilized, a head bond end 16 may be provided (e.g., as in FIG. 8A), and either 16 or 18 may be optionally provided with a feature that may function as a means for glue relief (e.g., as described above in connection with FIG. 4A). As shown by the contrast between the darker and lighter areas of this view, the flutes contained within this design are recessed from the outer surface of the lower tip section. These flutes or troughs extend only in the non-bond area and extend from the tip of the lower tip section up to the bond joint region where the two shafts are bonded together.

As described above, lower tip sections according to embodiments of the invention can have various combinations of cross-sectional geometry, joint end and head bond end. For example, FIG. 14B shows a fluted lower tip section 22 with head bond end 19 analogous to FIG. 14A, but with a smooth joint end 15 that is configured to slide into a coupler insert 24.

FIG. 16A is a cross-sectional view of the radial geometry of the lower tip section 22 examples according to some embodiments. In this configuration, the radial cross section is fluted which consists of six channels (flutes) that are equal distance apart and also taper from the head bond end increasing in depth and width up to the termination of the bond joint end where the upper and lower shaft sections are bonded. It is conceived that there are multiple variants possible of the radial cross-section covered for this invention. It is also expected that most if not all of the lower tip sections are tapering from the head bond end and increasing in diameter to the bond joint end where the upper and lower shaft sections are bonded together.

In other illustrative embodiments, as shown for example in FIG. 16B, the lower tip section 22 may be hollow (e.g., analogous to the hollow circular cross section shown in FIG. 10B and the hollow hexagonal cross section shown in FIG. 13B). FIGS. 14C, 14D, and 15B show embodiments analogous to those depicted in FIGS. 14A, 14B, and 15A, respectively, but wherein the lower tip section 22 has a hollow cross section in the radial direction (as indicated by the dotted lines).

FIG. 17 is an isometric view of an illustrative embodiment of a lower tip section 23. In this particular view, the solid tip section contains a joint end 18 with four convex semicircles that slide into the coupler insert 8 which then is bonded into the upper shaft section 7. The head bond end 18 also is configured with four convex semicircles that will slide into a coupler insert 8 which is then bonded into the head 5. This is an example of a bond end designed for a “Plumbers Neck” 5 or female bore into the head itself. If a second coupler insert is not utilized, a head bond end 16 may be provided (e.g., as in FIG. 8A), and either 16 or 18 may be optionally provided with a feature that may function as a means for glue relief (e.g., as described above in connection with FIG. 4A). This configuration 23 is an example of a longitudinal complex double bend geometry that is commonly used for putter shafts by creating an offset with the head itself.

FIG. 18A is an isometric view of another illustrative embodiment of a lower tip section 23. In this particular view, the solid tip section contains a joint end 18 with four convex semicircles that slide into the coupler insert 8 which then is bonded into the upper shaft section 7. The head bond end 19 is a smooth surface with a hole drilled in the center that is bonded over the head post 11. This is an example of a bond end designed for “Over Post” 11 head designs. If a second coupler insert 8 is utilized, a head bond end 17 may be provided (e.g., as in FIG. 9A). This configuration 23 is an example of a longitudinal complex double bend geometry that is commonly used for putter shafts by creating an offset with the head itself.

As described above, lower tip sections according to embodiments of the invention can have various combinations of cross-sectional geometry, joint end and head bond end. For example, FIG. 18B shows a lower tip section 23 with head bond end 19 analogous to FIG. 18A, but with a smooth joint end 15 that is configured to slide into a coupler insert 24.

FIG. 19 is a cross-sectional view of the radial geometry of the lower tip section 23 examples according to some embodiments. In this configuration, the radial cross section is circular. It is conceived that there are multiple variants possible of the radial cross-section covered for this invention. It is also expected that most if not all of the lower tip sections are tapering from the head bond end and increasing in diameter to the bond joint end where the upper and lower shaft sections are bonded together.

In some embodiments, the tip section of the two-piece shaft may be reinforced with a metal or alloy. The metal or alloy may be provided in various forms including, but not limited to, a mesh (e.g., as described in U.S. Patent Application No. 17/165,721) or a rod (e.g., a titanium retaining rod), and may span the entire length of the lower tip section, or may be provided on one or more portions of the lower tip section. For example, as shown in FIG. 20A, in some embodiments a layer of stainless steel metal mesh 42 may be provided, which spans the circumference and length of the tip section. As shown in FIG. 20A, the tip section is hollow circular, analogous to the embodiment shown in FIG. 8D (tip section 14 with joint end 15 and head end 16), but in other embodiments any of the lower tip sections described and shown herein may be similarly reinforced with metal. Adding a reinforcement such as a woven, knitted metal mesh alloy like stainless steel, titanium or aluminum to the inner circumference of the tip section of a two-piece golf shaft according to embodiments of the present invention during the molding process can help to further improve durability, stiffness, and the ability to alter the weight distribution on the tip section. Embedding the mesh material into the chopped carbon fiber/thermoplastic material of the tip section can dramatically improve the strength, spine, and torsional deflection of the tip section. Adding the mesh to the chopped carbon fiber/thermoplastic material during the molding process can also allow the tip section to utilize a lower density carbon fiber. Varying the number of wraps of the woven alloy mesh as well as the length of the mesh can alter the gradient of density throughout the tip section by changing the volume of metal mesh added to tip section.

In some embodiments, the metal reinforcement may comprise a woven metal mesh as described in U.S. patent application Ser. No. 17/165,721, which comprises stainless steel, nickel, titanium, copper, aluminum, magnesium, or an alloy thereof, and has at least 150×150 wires per square inch. In some embodiments, the woven metal mesh comprises wire having a diameter of about 0.001 inches to about 0.008 inches. In some embodiments, the woven metal mesh comprises wire having a diameter less than or equal to 0.001 inches. In various embodiments, the woven metal mesh may have, for example, a plain weave, Dutch weave, twilled weave, twilled Dutch weave, reverse Dutch weave, or five heddle weave. In some embodiments, the woven metal mesh may be annealed.

FIG. 20B is an isometric view of another illustrative embodiment of a lower tip section 14. In this particular view (analogous to FIG. 8A), the solid tip section contains a joint end 18 with four convex semicircles that slide into the coupler insert 8 which then is bonded into the upper shaft section 7. The head bond end 16 is a smooth surface with the absence of a hole drilled into the tip. This is an example of a bond end designed for a “Plumbers Neck” 5 or female bore into the head itself. The contrast between the darker area located at the head bond end 16 of the lower tip section 14 and the lighter shading at the bond joint end 18 represents a gradient in material density along the length 28. This demonstrates the ability to not only have a range of densities within a given lower tip section design, but the ability to change the longitudinal density from one end to the other end of the lower tip section.

As will be understood by one of ordinary skill in the art, the material density may be varied for any of the lower tip sections described and shown herein. For example, FIG. 20C shows a lower tip section 14 with joint end 15 and head bond end 16 (analogous to FIG. 8B), which has a gradient in material density along the length 28.

FIG. 21 shows a side view and two isometric views of the coupling insert 8, according to various embodiments of the invention. The side view of the coupling insert 8 shows that the length 30 (dl) of the insert can vary between one-half inch in length up to three inches in length with a preferred embodiment being approximately two inches in length. At the one end exists a flange 29 that flushes up with both the corresponding outer diameters of both the upper shaft section 7 and the respective lower tip section. Details 33 and 34 are shoulders that are preferably within 0.0005 inches under the inner diameter of both the bore hole in the head itself and the upper shaft section 7. This creates a virtual interference fit between the coupling insert and the upper shaft and is the primary method of centering the coupling insert into the shaft or head so that the axial straightness is maintained. These sections extend for approximately 0.010 inches in length, but can be longer depending on the overall length of the coupling insert 8. The center section 32 is an area of the coupling insert where the adhesive glue is applied for the bond joint. The graphical views of FIG. 21 show a knurled surface along the length (d3) whereby the peak of the knurl is at the same outer diameter as the two shoulders 33, 34. The valley of the knurled surface extends to minimum of 0.010 inches in depth compared to the maximum diameters of 32, 33, 34. Feature 31 represents the outer diameter (d2) of the shoulders 33, 34 and the knurled surface 32. The two isometric views of coupling insert 8 show both ends of the coupling insert and how the convex semicircular four-hole design extends from both ends of the insert 8. These concave semicircles are configured to accept the lower tip section bond joint end containing the four semicircular convex ridges to create a mechanical interlock between the upper shaft section and the lower tip section. In certain preferred embodiments, the coupling insert 8 is made out of aluminum or other metallic alloys, but is not limited to those materials, and in other embodiments may be formed from an injection moldable carbon fiber reinforced thermoplastic resin (e.g., KyronMAX) or other reinforced thermoplastic materials.

FIG. 22 is an end view 35 of the flange end of the coupling insert 8. This view shows the location and equal distance spacing of the four semicircular concave grooves 36 that are configured to accept the four semicircular convex ridges contained, for example, on the joint end 18 of the lower tip section. It is conceived that there are other alternate geometries that may be used to create an interlocking design, however this design is an example of a preferred embodiment.

FIG. 23 is an end view 37 of the insertion end of the coupling insert 8. This view shows the location and equal distance spacing of the four semicircular concave grooves 36 that are configured to accept the four semicircular convex ridges contained, for example, on the joint end 18 of the lower tip section. It is conceived that there are other alternate geometries that may be used to create an interlocking design, however this design is an example of a preferred embodiment.

FIG. 24 is an end view 38 of the geometry of the bond joint end 18 of the lower tip section containing four semicircular convex ridges 39 that are contained at the bond joint end of the tip section and in some configurations also located at the head bond end of the lower tip section. The four semicircles depicted are designed to act as a centering mechanism between the lower tip section, the coupling insert 8, and the upper shaft section 7. These ridges 39 also create a mechanical locking bond joint for added joint strength.

FIG. 25 shows a side view, cross-sectional view, end view, and two isometric views of the coupling insert 24, according to various embodiments of the invention. Illustrative dimensions of this embodiment are marked in mm. As shown, the length of the coupling insert 24 is approximately 69.77 mm (2.75 in). At the one end exists a head portion 25 (20.27 mm; 0.798 in) that flushes up with the corresponding outer diameters of both the upper shaft section 7 and the respective lower tip section. As shown the inner diameter of head portion 25 is 11.93 mm (0.470 in) and the outer diameter is 14.224 mm (0.56 in). Stem portion 26 (49.50 mm; 1.95 in) is configured for insertion into the upper section 7 essentially as described above for coupling insert 8. The two isometric views of coupling insert 24 show both ends of the coupling insert. As shown, for example, in the cross-sectional view taken along A-A and the end view 27 of the insertion end of the coupling insert 24, both the head portion 25 and the stem portion 26 have a smooth interior surface configured to accept a smooth joint end 15 on the lower tip section of the shaft. In certain preferred embodiments, the coupling insert 24 is made out of aluminum or other metallic alloys, but is not limited to those materials, and in other embodiments may be formed from an injection moldable carbon fiber reinforced thermoplastic resin (e.g., KyronMAX) or other reinforced thermoplastic materials.

FIG. 26A illustrates a golf club set of irons 40 comprising hybrid shafts according to embodiments of the present invention 3 assembled into a set of iron heads 6. Shafts according to embodiments of the present invention 3 can be constructed based upon many variants described herein (see, e.g., FIG. 26B which shows an iron shaft analogous to the putter shaft of FIG. 4B). This illustration depicts a possible scenario whereby the length of the lower tip section and the length of the upper shaft section can be oriented to be in a descending, ascending, or constant location throughout a set of irons. What is uniform is that the hybrid shaft would still be bonded in the same fashion with the same coupling insert. The length and location of the lower tip section relative to the upper shaft section is determined by the desired performance of the club itself and the type of player that the club is designed for.

FIG. 27A illustrates a golf club set of drivers and fairway woods 41 comprising hybrid shafts according to embodiments of the present invention 4 assembled into a set of driver heads 44. Shafts according to embodiments of the present invention 4 can be constructed based upon many variants described herein (see, e.g., FIG. 27B which shows a driver shaft analogous to the putter shaft of FIG. 4B). This illustration depicts a possible scenario whereby the length of the lower tip section and the length of the upper shaft section can be oriented to be in a descending, ascending, or constant location throughout a set of drivers and fairway woods. What is uniform is that the hybrid shaft would still be bonded in the same fashion with the same coupling insert. The length and location of the lower tip section relative to the upper shaft section is determined by the desired performance of the club itself and the type of player that the club is designed for.

While there have been shown and described fundamental novel features of the invention as applied to the preferred and illustrative embodiments thereof, it will be understood that omissions and substitutions and changes in the form and details of the disclosed invention may be made by those skilled in the art without departing from the spirit of the invention. Moreover, as is readily apparent, numerous modifications and changes may readily occur to those skilled in the art. For example, various features and structures of the different embodiments discussed herein may be combined and interchanged. Hence, it is not desired to limit the invention to the exact construction and operation shown and described and, accordingly, all suitable modification equivalents may be resorted to falling within the scope of the invention as claimed. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

TWO-PIECE GOLF SHAFT

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