WO1999002223A1

WO1999002223A1 - Plug for stressing golf club shaft

Info

Publication number: WO1999002223A1
Application number: PCT/US1998/014266
Authority: WO
Inventors: Lyle Smith
Original assignee: Lyle Smith
Priority date: 1997-07-09
Filing date: 1998-07-09
Publication date: 1999-01-21
Also published as: AU8183398A

Abstract

A golf club with a hollow shaft (12) with a bore (16) therein, a club head (24) at one end of the shaft (12) and possibly a grip (36) at the other end. A short length plug (30) of a diameter slightly greater than the inner diameter of the bore (16) is forced into the bore (16) to a point of usage (32) selectively at or away from the center of flexure of the club (10). The location of the plug (30) is selected to adjust the recovery of the club shaft (12) by creating a stress field at the point of usage (32).

Description

PLUG FOR STRESSING GOLF CLUB SHAFT

CROSS REFERENCE TO PROVISIONAL APPLICATION:

This application claims the benefit of U.S. Provisional Application No. 60/052,075, filed July 9, 1997.

BACKGROUND OF THE INVENTION

The invention concerns a shaft, particularly a golf club shaft, whether the shaft is made of composite materials, metals or any combination thereof, or any type of shaft that is long and thin, wherein during the practical use of the shaft, it would be desirable to alter the recovery characteristics of the shaft during the golf swing.

The elongated shaft of a golf club can be bent or curved along its length, and that is flexion of the shaft. In addition, the shaft can be twisted around its length axis. This often occurs when a golf ball is hit. Also, when a club is swung and the club head strikes the ground prior to contacting the ball, the club shaft can be twisted. The above described twisting is the torque of the golf club. The speed at which the club shaft restores itself after the torque is applied does have an effect on the direction of the face of the club head when it strikes a ball and therefore an effect upon the direction in which the ball flies.

It is desirable to reduce the torque of the golf club. It is also desirable to control the speed at which a twisted shaft restores itself from being twisted. Different golf club manufacturers try to control the torque to different extents for the different types of clubs in a set, for clubs of particular materials, and for clubs of different lengths, etc. To what extent the torque should be controlled and on which types of clubs is a decision for a particular golfer and/or a particular club manufacturer. In order to control its torque, a golf club shaft sometimes has to be made so stiff that it is not usable by the average golfer. Consequently, some golf club shafts are too stiff while others are so flexible as to permit too much torque.

BRIEF DESCRIPTION OF THE INVENTION

This invention is particularly concerned with a shaft and the method of its manufacture, and specifically concerns a golf club shaft and the manufacture of a golf club shaft, wherein the shaft will have the desired lack of stiffness, the desired resistance to torque and the desired restoration speed after it has been twisted around the shaft axis . These facts are important to golfers because less stiffness can enable greater length hits, while greater torque resistance can create more accurate hits.

A golf club shaft is normally a hollow tubular shaft with a tapered bore running its full length. The club has a center of flexure between the head and the g ip- A point of usage, described below, may be at the center of flexure or may be above or below the center of flexure, anywhere between the club head and the grip. The point of usage is selected for a particular type club, that is for different types of clubs with different angled club heads and different shaft lengths, different shaft compositions and different shaft characteristics, as discussed below. The invention is concerned with controlling the recovery of a shaft with a hollow bore in it, particularly a golf club shaft. The shaft is tested to determine its main flex point or main center of flexure. A short length plug is inserted through the open end of the shaft into the bore and is pressed to a point of usage in the bore which may be at or above or below the main flex point of the shaft. The outside diameter of the plug is slightly greater than the inside diameter of the bore at the selected point of usage. The plug is resistant to yielding under pressure. The inserted plug creates a stress field at the point of usage providing control of the recovery and greater club stability. That stress at the point of usage affects the timing of the shaft to recover to its normal position. Although the invention is described with reference to a golf club shaft, it can be used in other shafts having a comparable need for recovery control .

BRIEF DESCRIPTION OF THE DRAWING Figure 1 shows a partial cross-section through a golf club incorporating the invention with the separations showing it is of greater length.

DESCRIPTION OF A PREFERRED EMBODIMENT

Assembly of a golf club 10 including the invention is now described.

Before a golf club shaft 12 has the invention applied to it, there is no stress on the shaft.

First, one end 22 of the shaft 12 is glued into the head 24 of the golf club, such a^*s a driver or another club head. This applies no stress on the outside of the shaft 12. The shaft is tested to determine the main flex point 26 along the shaft e.g., where its main center of flexure is located. Through the open end 28 of the shaft away from the club head 24, a short length plug 30, for example 3/8th inch or 10mm. in length, is inserted into the bore 16 of the shaft 12 and is pressed to the point of usage 32 which may be at or below or above the flex 26 point of the shaft. In the drawing, the plug 30 is shown in a solid line below the main flex point 26, but may be at or may be above the flex point 26, as shown at alternative plug position 30a. The outside diameter of the plug 30 is greater than the inside diameter of the bore 16 of the shaft at the selected point of usage 32, and depending on the desired usage of the club as described below, the plug is particularly in the range of .002 to .007 inch or .050 mm to .175 mm larger in outside diameter than the inside diameter of the bore at the point of usage. But the diameter difference could even be larger. The material of the plug 30 may be any material which is resistant to yielding under pressure. Examples are selected from the group consisting of metal e.g., aluminum, and plastic, rubber, wood, composite material, graphite fiber material, ceramic, and materials specifically designed to expand and to maintain that expansion due to applied temperature. A preferable material, however, would be a like material of the shaft since a plug is less likely to wear against a shaft of the same material. It would be ideal to have the materials of the plug and the interior diameter of the shaft of the same composition. For example, if the shaft is a graphite fiber shaft, then it is preferable to have the plug be comprised of graphite fibers. After the plug has been positioned and secured, the grip 36 of the handle is applied at the top end 28.

When the plug 30 is forced into the bore 16 by an application of considerable force on the plug, the plug creates a "stress field" in the club shaft where the plug is positioned i.e., at the point of usage. Stress can be described as "torque resistance" . The applied stress creates greater stability in the club when the shaft is swung than would be its stability with an unstressed or less stressed shaft. Instead of the shaft having zero pounds of resistance to torque, it may have as much as 60,000 pounds of applied stress that causes resistance to torque, or perhaps more or less stress, depending on the diameter of the plug insert with reference to the interior diameter of the shaft bore at the point of usage and depending on the materials which might be used in a golf shaft which could withstand greater or lesser pressures. For example, a graphite fiber shaft would be able to withstand perhaps 60,000 lbs. of pressure applied by the plug before the shaft bursts. A larger diameter plug in a bore applies more pressure. Since greater stress reduces torque, the diameter of the plug relative to the diameter of the bore changes the stress field and the torque recovery of the shaft. The diameter of the plug is selected so as to desirably stress the shaft or its fibers without causing bursting of the club shaft. Other materials are more or less resistant to bursting and the diameter of the plug is selected with reference to the pressure being applied and the burst strength of the material of the shaft at the point of usage.

The primary feature of the invention is the creation of the stress field at the location of the plug 30 along the shaft 12, at the point of usage 32. When the material is stressed at the point of usage, it alters the ability of the shaft to recover from torque.

A golf club shaft which has had torque applied to it tends to return to its untwisted condition or its torque free condition. A plug placed to create the stress field will cause the club to restore to the untorqued condition more rapidly. This can make a difference as to the direction in which the ball flies, because the shaft could be twisting to return or be fully returned when it hits the ball and the angle at which the ball flies will be affected.

For different golf clubs, like drivers, irons, even putters, and for clubs with different club face angles and different shaft lengths, different torque resisting requirements must be satisfied. This requires selecting the plug diameter and point of usage for each club according to its torque requirements.

Only a single plug 30 is intended to be placed in the position at the point of usage 32. Within the invention, more than one plug might positioned to extend the stress field over a greater length of the club shaft or apply stress at various usage points along the club shaft . The invention is useful for controlling the recovery from torque in any golf club shaft wherein applying force radially outward from the bore of the shaft will stress the shaft.

Although the present invention has been described in relation to a particular embodiment thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims .

Claims

WHAT IS CLAIMED IS:

1. A golf club comprising: an elongated, hollow shaft with a bore inside it extending along its length; a golf club head at one end of the shaft and a grip at the other end of the shaft; the shaft having a center of flexure between the head and the grip; a plug installed in the bore at a point of usage selectively at or off the center of flexure of the shaft, the plug being of a material which is resistant to yielding under pressure applied to the plug in the bore, the plug having a diameter greater than the diameter of the bore at the point of usage so that the plug creates a stress field in the shaft at the point of usage to alter the recovery characteristics of the shaft differently than the shaft would have if the plug were not present.

2. The golf club of claim 1, wherein the plug is short in length in comparison with the length of the shaft .

3. The golf club of claim 2, wherein the plug and the point of usage are below the center of flexure of the club.

4. The golf club of claim 2, wherein the plug and the point of usage are above the center of flexure of the club.

5. The golf club of claim 1, wherein the plug is comprised of a material selected from the group consisting of metal, plastic, rubber, wood, composite material, ceramic and materials specifically designed to expand and to maintain that expansion due to applied temperatures .

6. The golf club of claim 1, wherein the shaft is comprised of a material and the plug is comprised of the same material .

7. The plug of claim 1, wherein the shaft is comprises of graphite fiber and the plug is comprised of graphite fibers .

8. A method for assembling a golf club with controlled recovery comprising: providing a hollow golf club shaft having a bore extending along its length, the club shaft having a center of flexure along its length_s- determining the center of flexure along the length of the shaft; inserting a short length plug into the bore of the shaft to a point of usage which is at or off the center of flexure of the shaft, the point of usage being selected to establish a stress field at a particular location along the shaft and for selecting a particular recovery for the shaft; applying a golf club head to one end of the shaft.

9. The method of claim 8, wherein the club head is applied to the shaft before the center of flexure is determined.

10. The method of claim 9, wherein the grip is applied to the shaft after the plug is positioned at the point of usage .

11. The method of claim 10, wherein the plug is moved to the point of usage along the bore.

12. The method of claim 10, wherein the plug is moved into the bore to a point of usage below the center of flexure, and the point of usage is selected for achieving a recovery.

13. The method of claim 12, wherein the point of usage is selected dependent upon the type of club, the club face angle, the shaft length and the torque requirements for the particular club.

14. The method of claim 8, further comprising applying a grip at the other end of the shaft .

15. A shaft with controlled recovery, comprising: the shaft being hollow with a bore extending along its length, the shaft having a center of flexure; a plug installed in the bore at a point of usage selectively at or off the center of flexure of the shaft, the plug being of a material which is resistant to yielding under pressure applied to the plug in the bore, the plug having a diameter greater than the diameter of the bore at the point of usage so that the plug creates a stress field in the shaft at the point of usage to alter the recovery characteristics of the shaft differently than the shaft would have if the plug were not present.

16. A method for assembling a shaft with controlled recovery, comprising: providing a hollow shaft having a bore extending along its length, the shaft having a center of flexure along its length; determining the center of flexure along the length of the shaft; inserting a short length plug into the bore of the shaft to a point of usage which is at or off the center of flexure of the shaft, the point of usage being selected to establish a stress field at a particular location along the shaft and for selecting a particular recovery for the shaft .