U.S. patent application number 10/915512 was filed with the patent office on 2005-01-13 for golf club shaft with adjustable flex.
Invention is credited to Hodgetts, George W..
Application Number | 20050009620 10/915512 |
Document ID | / |
Family ID | 33563614 |
Filed Date | 2005-01-13 |
United States Patent
Application |
20050009620 |
Kind Code |
A1 |
Hodgetts, George W. |
January 13, 2005 |
Golf club shaft with adjustable flex
Abstract
A hollow golf club shaft and a moveable solid shaft insert about
6 to 24 inches long wherein the depth of insertion of the shaft
insert into the shaft may vary from about 1 to 10 inches. Changing
the location of the shaft insert allows a player to change the flex
of the shaft and thereby optimize the performance of the club
dynamics to the player. The shaft insert is initially held in place
by friction between the shaft and the shaft insert, optionally with
a joining agent located therebetween, until a final setting of the
shaft insert is determined. Then the shaft insert is permanently
located within the shaft to make the club legal for play under
U.S.G.A. Rules. Shaft fitting can be administered by a player with
or without coaching and can be revisited at any time prior to
permanent attachment by a simple adjustment. The shaft inserts are
useful on all hollow shaft clubs, from putter to driver, and can be
retrofitted to existing clubs without removing the grip.
Inventors: |
Hodgetts, George W.;
(Newton, MA) |
Correspondence
Address: |
Jacobs Patent Office
P.O. Box 390438
Cambridge
MA
02139
US
|
Family ID: |
33563614 |
Appl. No.: |
10/915512 |
Filed: |
August 9, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10915512 |
Aug 9, 2004 |
|
|
|
10366854 |
Feb 14, 2003 |
|
|
|
Current U.S.
Class: |
473/300 |
Current CPC
Class: |
A63B 60/10 20151001;
A63B 60/06 20151001; A63B 60/08 20151001; A63B 60/42 20151001; A63B
60/48 20151001; A63B 53/14 20130101; A63B 53/10 20130101; A63B
60/22 20151001 |
Class at
Publication: |
473/300 |
International
Class: |
A63B 053/14 |
Claims
What is claimed is:
1. A method of adjusting the flex of a golf club shaft to produce a
golf club which has radially equal shaft flex and is acceptable for
play by the rules of the U.S. Golf Association, wherein said golf
club comprises a golf club shaft having a first end attached to a
grip section and a second end attached to a club head, said golf
club shaft being of tubular cross section and containing an
elongated cavity extending from about the grip section to about the
club head; said method comprising (i) placing a rigid tubular shaft
insert having a length of about 6 to 24 inches inside the golf club
shaft from the first end, (ii) adjusting the penetration of the
tubular shaft insert within the shaft from about 1 inch to about 10
inches to obtain a desired amount of flex for a player, and (iii)
attaching the shaft insert within the shaft so that it can not be
moved during play of a round of golf.
2. The method of claim 1, wherein the rigid tubular shaft insert is
hollow.
3. The method of claim 2, wherein the rigid tubular shaft insert is
made of a material selected from the group consisting of aluminum,
titanium, and graphite.
4. The method of claim 1, wherein the rigid tubular shaft insert in
solid.
5. The method of claim 4, wherein the rigid solid tubular shaft
insert is made of graphite.
6. The method of claim 1, wherein a compressible joining agent is
located between the golf club shaft and the shaft insert.
7. The method of claim 6, wherein the compressible joining agent is
a silicone adhesive.
8. The method of claim 7, wherein the silicone adhesive is placed
on a portion of the shaft insert outer surface before the shaft
insert is inserted into the golf club shaft.
9. The method of claim 8, wherein the silicone adhesive on the
shaft insert outside surface is allowed to cure before the shaft
insert is inserted into the golf club shaft.
10. The method of claim 1, wherein the shaft insert is about 10 to
18 inches long.
11. The method of claim 10, wherein the shaft insert is located
about 2 to 6 inches from the grip end.
12. The method of claim 1, wherein after an adjustment of the
extent of penetration of the shaft insert, a player uses the club
to hit golf balls.
13. The method of claim 12, wherein after an adjustment of the
extent of penetration of the shaft insert, the flex of the club is
determined.
14. The method of claim 13, wherein additional golf clubs are
prepared having the determined flex.
15. The method of claim 1, wherein after an adjustment of the
extent of penetration of the shaft insert, the flex of the club is
determined.
16. The method of claim 15, wherein additional golf clubs are
prepared having the determined flex.
17. The method of claim 1, wherein the shaft insert is selected
from a group of shaft inserts of varying lengths, stiffness,
longitudinal shape, cross section, and material.
18. The method of claim 1, wherein the shaft insert is of
sufficient diameter and purchase to hold itself in place during
practice when said golf club shaft and said shaft insert are used
as an assembly in a finished golf club.
19. The method of claim 1, wherein the golf club shaft has a grip
on the grip end and a central portion of the grip at the grip end
is removed prior to inserting the shaft insert.
20. The method of claim 1, wherein the shaft insert is shaped so
that during bending of the golf club shaft during a golf swing, a
central section of the shaft insert contacts the golf club
shaft.
21. A golf club prepared by the method of claim 1.
22. A golf club comprising a tubular hollow shaft with a grip end
and a club head end, a rigid tubular shaft insert inserted into the
grip end of the hollow shaft, said shaft insert being about 6 to 24
inches long and shaped so fit within the shaft beginning at a
distance of 1 to about 10 inches from the grip end, and is held in
place by friction.
23. The golf club of claim 22, wherein the shaft insert is movable
within the shaft from a first location to a second location and
changes the flex of the club.
24. The golf club of claim 22, further containing a compressible
joining agent between the shaft interior surface and the shaft
insert exterior surface.
25. The golf club of claim 24, wherein the compressible joining
agent is a silicone adhesive.
26. The golf club of claim 22, wherein the shaft insert is
permanently attached to the shaft.
27. The golf club of claim 22, wherein the shaft insert is about 10
to 18 inches long.
28. The golf club of claim 22, wherein the shaft insert is attached
to the golf club shaft within the shaft by means of an
adhesive.
29. The golf club of claim 22, wherein the shaft insert is shaped
so that during bending of the golf club during a golf swing a
central section of the shaft insert contacts the golf club
shaft.
30. A method of retrofitting a golf club to change the flex of the
club, said club having a tubular hollow shaft with a grip end and a
club head end, a grip attached onto the grip end, a club head
attached to the club head end, said method comprising the steps of:
(i) cutting a plug hole having a diameter of about 0.55 inches out
of the grip surface abutting the tubular hollow shaft grip end,
(ii) inserting, a rigid tubular shaft insert through the plug hole
into the grip end of the hollow shaft, said shaft insert being
about 6 to 24 inches long and shaped to fit within the shaft a
distance of 1 to about 10 inches from the grip end, and is held in
place by friction.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation-in-part of U.S.
application Ser. No. 10/366,854, filed Feb. 14, 2003.
BACKGROUND OF THE INVENTION
[0002] This invention relates to golf clubs, golf club shafts, a
rigid tubular insert placed within a golf club shaft so as to be
free-floating, and to a method of adjusting the overall shaft flex,
wherein the resulting golf clubs fully comply with the rules of the
U.S. Golf Association for play.
[0003] Several technical specifications are commonly used to
describe golf clubs: total weight, swing weight, length, loft
angle, lie angle, head size and weight, grip diameter, and shaft
flex. But the proper selection of the latter is generally
acknowledged to be most important when fitting clubs to a golfer.
Moreover, recent studies have shown that it is very important for
custom golf club fitters to find the optimum flex for each player
for improved shot control and greater distance. But finding the
optimum flex has perplexed most teachers, club fitters and
golfers.
[0004] Three methods for finding the best flex before club assembly
presently dominate the market for custom clubs. In the first
method, the player swings one club several times and the average
club head speed measured and used to calculate the flex for the
entire club set. The second approach relies on matching one club or
a set of clubs to a player's favorite club. In the third method, a
player hits several shots with calibrated test clubs, finally
selecting the best of the lot to serve as a model for his set,
which can be matched to it. Once the clubs are constructed, they
can only be used with minor adjustment until another set is
purchased, prompted in many cases by the golfer's belief that a
better fit is probable.
[0005] Most misfits of clubs to players, the rule rather than the
exception, are mostly due to the methods available rather than to
poor club fitters. U.S. Pat. No. 5,821,417 to T. Naruo et al (Oct.
13, 1998), concludes that many factors other than club head speed,
such as shaft strain at impact, swing time, and acceleration,
effect the choice of optimum flex for each player. Yet the most
popular flex fitting method in use today calculates shaft flex
solely from club head speed. This same study concedes that there is
a best flex for every player, but points out the difficulty in
determining it. If this conclusion is correct, it would suggest
that a method for altering the flex after the club is constructed,
through trial and error to reveal the best flex, might be a
benefit.
[0006] Heretofore, there have been several attempts to modify the
flexural characteristics of golf shafts after club assembly by
adding either fixed or adjustable materials to either the outer or
the inner surface of the shaft. Almost all of these attempts which
add material to the outer surface of the shaft are accompanied by
adverse cosmetic results. Those which attempt to change the shaft
frequency from inside the shaft have been too heavy, too expensive,
violate the present rules of golf, or cannot achieve the results
promised.
[0007] Thus there remains a need for a system which will allow
accurate adjustment of the flexural characteristics while not
adversely effecting the club weight and while still conforming to
the rules of the U.S. Golf Association so that the club is
"tournament-qualified" for use in competitive play, i.e. during
rounds used to establish a golfer's handicap and golf tournaments.
The USGA rules specifically require that (1) the club shaft exhibit
uniform properties in all directions from the axis of the shaft and
(2) the club contain no movable parts.
[0008] The prior art advocates of adjusting the flex of a golf club
in practice or play have focused on trying to maximize the transfer
of energy stored in the flexing of the shaft by somehow arranging
to have the shaft straight at impact. Negating this theory, many
studies have found that all swings, for all golfers, with all golf
clubs tested, feature the shaft bent toward the target just before
impact, well past the point where energy stored in a shaft could be
transferred to the ball. This means that the job of the shaft is,
evidently, not to store energy for later use. But the shaft does
bend and rotate during a golf swing and clearly it influences the
result. Many granted patents have been alleged to adjust shaft
dynamics and the most important ones are listed below.
[0009] Several attempts have been made to adjust shaft flex by
adding assemblies to a conventional shaft of a club. One of the
oldest shaft flex adjuster employs an external wire and bridge seen
in U.S. Pat. No. 4,685,682 of J. Isabell (Aug. 11, 1987), which has
several limitations including a poor cosmetic look.
[0010] An attempt to improve the cosmetic appearance of a flex
adjuster is seen in U.S. Pat. No. 6,113,508 of M. Locarno et al
(Sep. 05, 2000), which employs an internal eccentric stiffening rod
having a different, lateral stiffness at right angles. The clubs
produced by this method violate the USGA rules of golf because the
patent deliberately causes the shaft flex to be radially unequal in
shape as well as, specifically, in flex. Moreover, the method is
flawed by the fact that stiffness can be transferred from one plane
to the other, but both cannot be adjusted independently. This can
lead to mixed results in use.
[0011] Another method for modifying flex entails adding a
stiffening rod to the inside of a shaft, e.g. U.S. Pat. No.
3,833,233 of R. Shulkin (Sep. 03, 1974). Varying lengths of shaft
elements are inserted into clubs used specifically for fitting flex
to a player. The inserted shaft elements are not to be adjusted in
their position once in place, but only exchanged and are not
intended to be present in a set of clubs during play. Rather, the
elements are only to be used for fitting.
[0012] In U.S. patent application Ser. No. 2001/0005696 of M.
Hendrick (Jun. 28, 2001), a short, generally 1-3 inch long, hollow
shaft insert is used to change the swing weight of a club. It can
be readjusted at any time, but does not, of itself, have any impact
on the swing characteristics of the club other than swing weight.
The patent specifically excludes changing the shaft flex using this
design.
[0013] U.S. Pat. No. 5,478,075 of C. R. Saia et al (Dec. 26, 1995)
describes a method of changing shaft flex using an insert with
radially expandable rubber discs that can be expanded by turning a
threaded energizing rod. The rubber discs are stationary as they
expand and do not move in or out of the outer shaft.
[0014] U.S. Pat. No. 6,361,451 of B. Masters et al (Mar. 26, 2002),
U.S. Pat. No. 6,241,623 to C. Liabangyang (Jun. 05, 2001), and U.S.
Pat. No 6,394,909 to C. Laibangyang (May 28, 2002) utilize a wire
strung down the center of a golf shaft the tension of which is
adjustable to exert varying compressive forces on the shaft thereby
seeking to change its flex. The three inventions allow players to
adjust flex in order to deliver more energy stored in the flex at
ball impact, a near impossibility in practice, as mentioned
earlier.
[0015] Another attempt to change the overall flex and also dampen
the shock effect of a ball strike from the club head to the hands
is referred to in U.S. Pat. No. 5,083,780 of T. C. Walton et al
(Jan. 28, 1992). In this patent, the grip end is reinforced by a
cylinder placed between the grip and the shaft under the grip
thereby lowering the flex point, increasing the flex and dampening
vibrations from the club head to the hands. Once set, it is not
adjustable in practice or play.
[0016] U.S. Pat. No. 6,045,457 of T. Soong (Apr. 04, 2000)
discloses a method of inserting a second shaft inside a bulged
outer shaft to increase the flex of the resultant shaft
combination. The patent claims that the resultant fixed amount of
increase in flex and lowering of the flex point increases club head
speed. The bulged outer shaft serves to ensure that the second
shaft only contact the main shaft at the two ends of the second
shaft, i.e. the middle section of the second shaft does not contact
the main shaft. The increased flex occurs when the end of the
second shaft closest to the clubhead makes contact with the outer
(main) shaft. The force exerted by the second shaft is due only to
rigidity of the insert because the insert is anchored at its butt
end at the grip and only touches the outer shaft at the opposite
end. This differs from the present invention wherein at least three
locations of the shaft insert must contact the outer shaft during a
swing.
[0017] U.S. Pat. No. 5,054,781 of T. Soong (Oct. 08, 1991)
discloses a method of building a shaft with a fold back shaft that
is inserted and contacts the inner wall of the outer shaft only
after some degree of shaft bending. The claim of increased energy
storage and release at ball contact is dubious, and while it
employs an insert to change the flex of the shaft, once set, it is
not adjustable.
[0018] U.S. Pat. No. 6,056,646 of T. Soong (May 02, 2000) employs a
fixed insert to stiffen the flex of the outer golf shaft but is
non-adjustable once installed. It is intended to stiffen the flex
only when the shaft is flexed beyond a certain point. When the tip
of the insert is in contact with the outer shaft, the flex is
increased.
[0019] Many other patents feature shaft inserts that are primarily
concerned with damping high frequency vibrations transmitted from
the club head to the hands.
[0020] None of the prior art has succeeded in creating a practice
golf club in which a player can repeatedly adjust the flex and play
with that club until such time as the player (or some third party)
determines that the club performance is maximized and then convert
that practice golf club into a golf club which is 100% legal under
USGA Rules for tournament play.
[0021] Accordingly, it is the object of this invention to provide a
means which will enable a player to adjust the shaft flex of a golf
club during practice and non-regulation play in order to discover
the best shaft flex for that player.
[0022] It is the further object of this invention to provide means
of eliminating further shaft flex adjustments during play in
competition in order to conform the Rules of Golf of the USGA which
require a golf club shaft to "bend in such a way that the
deflection is the same regardless of how the shaft is rotated about
its longitudinal axis." (Appendix II, Section 2b(i))
[0023] It is the further object of this invention to provide the
means for a fixed insert to be used to increase the flex of a golf
club shaft by predetermined amounts.
[0024] It is the further object of this invention to provide the
best golf club shaft flex for each individual player and to provide
a means to do so in the form of a multiplicity of alternative
adjustable embodiments.
[0025] Still further objects and advantages will become apparent
from a consideration of the ensuing description and accompanying
drawings
DRAWINGS--BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a plan view of a golf club with a shaft insert in
place.
[0027] FIG. 2a is an expanded view of section cc in FIG. 1.
[0028] FIG. 2b is an expanded view showing the section of FIG. 2a
during a golf swing.
[0029] FIG. 2c is a graph showing the changing direction of bending
of a golf club during a swing.
[0030] FIG. 3 is a plan view of the preferred embodiment.
[0031] FIG. 4 is an end view of section 4-4 of FIG. 3.
[0032] FIG. 5a is an end view of a shaft insert of this invention
(legal for play under U.S. Golf Association Rules, Appendix II,
2b.
[0033] FIG. 5b is not an example of this invention. It is an end
view of a shaft insert which is illegal under U.S. Golf Association
Rules.
[0034] FIG. 5c is not an example of this invention. It is an end
view of a shaft insert which is illegal under U.S. Golf Association
Rules.
[0035] FIG. 6 is a plan view of a shaft insert adjuster in
place.
[0036] FIG. 7 is a plan view of a first alternative joining agent
embodiment
[0037] FIG. 8 is and end view of section 8-8 of FIG. 7.
[0038] FIG. 9 is a plan view of a second joining agent alternative
embodiment.
[0039] FIG. 10 is an end view of the section 10-10 of FIG. 9.
[0040] FIG. 11 is a plan view of a third joining agent alternative
embodiment.
[0041] FIG. 12 is and end view of section 12-12 of FIG. 11.
[0042] FIG. 13 is a plan view of a fourth joining agent alternative
embodiment
[0043] FIG. 14 is an end view of the section 14-14 of FIG. 13.
[0044] FIG. 15 is a plan view of a fifth joining agent alternative
embodiment.
[0045] FIG. 16 is a plan view of a thread holding agent alternative
embodiment.
[0046] FIG. 17 is an end view of the section 17-17 of FIG. 16.
[0047] FIG. 18 is a plan view of the threaded adjuster in
place.
[0048] FIG. 19 is a plan view of a universal shaft insert
embodiment.
[0049] FIG. 20 is a graph of the results of Example 1. FIG. 20a is
a graph showing the performance of a player using a club not
containing a shaft insert of this invention. FIG. 20b is a second
graph showing the effect of inserting a shaft insert into the club
of FIG. 20a and then changing the location of that shaft insert
within the club shaft upon the same player.
DRAWINGS--REFERENCE NUMERALS
[0050] 10 golf club shaft
[0051] 12 grip
[0052] 14 club head
[0053] 16 shaft insert
[0054] 17 insert adjuster
[0055] 18 joining agent
[0056] 20 grip plug
[0057] 22 threaded adjuster
[0058] 24 stop
[0059] 26 self-tapping threads
[0060] 28 thread holding agent
[0061] 30 torquer
[0062] 31 grip end force
[0063] 32 central shaft insert force
[0064] 33 club end force
SUMMARY OF THE INVENTION
[0065] The object of the invention is achieved by placing a
moveable rigid shaft insert in the hollow portion of the grip end
of a golf club shaft or a finished golf club. While shafts might be
specially constructed to facilitate the deployment of the present
invention, the invention is best used with standard shafts. A
suitable insert is a uniform piece of rigid material about 6 to 24
inches, preferably about 10 to 18 inches, and most preferably about
12 to 16 inches long, having (i) the same deflection regardless of
how the shaft insert is rotated about its longitudinal axis and
(ii) a smaller diameter than the golf club shaft into which it is
inserted. By changing the depth of penetration P of the shaft
insert between about 1 to 10 inches, the flex of a golf club can be
adjusted to a particular player's swing dynamics to achieve better,
i.e. more uniform, performance. The insert is firmly fixed in place
within the shaft and there is little to no likelihood of it working
loose during a round of golf. However, it can be intentionally
unfixed and thus the fitting of the club to the player can be
revisited at any time by a simple re-adjustment process.
[0066] This invention can be used on any clubs with hollow shafts
from putters to drivers. It can also be retrofitted into existing
clubs by enlarging the hole in the butt end of the grip using a
simple tool to cut out a plug, inserting an adjustable shaft
insert, determining the preferred location of the shaft insert
within the shaft, fixedly attaching the shaft insert to the shaft,
and if desired replacing the plug, thereby rendering the shaft
insert hidden and un-adjustable during play.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0067] As shown in FIG. 1, a conventional golf club comprises a
golf club shaft 10, usually about 34 to 46 inches in length, having
a grip 12 at the butt end and a club head 14 at the tip end of said
golf club shaft. A club head may be a "wood" head or an "iron" club
head, both or which can be manufactured from a variety of materials
including metals, wood, composites, graphite and polycarbonate or
combinations of materials. Shafts are constructed from a variety of
materials, mostly steel, aluminum, graphite, or titanium. They are
usually tapered but must be of homogeneous circular cross section
and have equal stiffness in all orthogonal directions in order to
conform to the current rules governing competition enforced by the
U.S. Golf Association.
[0068] Shaft materials have a high strength to weight ratio to
minimize the overall weight of the club while providing the
necessary rigidity for desired performance. To accomplish this,
common shaft manufacturing techniques require a thin wall
construction with a circular cavity in the center of the golf club
shaft 10. The existence of this cavity creates the opportunity for
this invention, namely, the placement of a shaft insert 16 within
the cavity as shown in FIG. 1 and in detail in subsequent
figures.
[0069] Refer now to the preferred embodiment of the invention shown
in FIG. 2a (with the grip 12 and the grip plug 20) and FIG. 3
(without the grip), which are expanded drawings of section cc of
FIG. 1. In both figures, the shaft insert 16 is positioned inside
the hollow cavity of the golf club shaft 10. The outer surface of
the shaft insert 16 may be grooved to provide friction fitting
between the insert and the shaft.
[0070] Adjusting the insertion depth P of an about 6 to 24 inch
long shaft insert from about 1 to 10 inches will change the overall
flex of the shaft of the golf club without altering its accepted
cosmetic look. Once positioned, the shaft insert 16 is firmly fixed
at the desired penetration depth P such that there is no reasonable
likelihood of them working loose during a round of golf. This may
be accomplished by friction alone if the shaft insert has the same
shape but a smaller diameter as the shaft into which it is to be
placed. However, use of a joining agent as explained further below
is preferred.
[0071] Golf shafts with no taper or minimal taper will allow
maximum range of insertion for shaft insert materials, especially
if the shaft insert material offers minimal compressibility.
Reduction in the outer shaft diameter due to tapering may
eventually limit further insertion of the shaft insert.
[0072] FIG. 5a shows the cross-sectional shape of a golf club 10
with a solid shaft insert 16 in place. While a tubular shaft insert
configuration is preferred (as shown in FIGS. 1-4) due to its
strength-to-weight ratio advantage, solid cross-section
configurations as shown may enjoy a cost advantage.
[0073] FIGS. 5b and 5c show two comparison shaft insert
configurations which are not within the scope of this invention
because they are do not comply with U.S. Golf Association Rule,
Appendix II, 2b. which requires that "along its length, a shaft
shall:
[0074] "(i) bend in such a way that the deflection is the same
regardless of how the shaft is rotated about its longitudinal axis;
and
[0075] "(ii) twist the same amount in both directions."
[0076] These comparison inserts fail to satisfy both
requirements.
[0077] As best seen shown in FIG. 6, the extent of penetration P of
a shaft insert within a shaft can be adjusted with insert adjuster
17. It can be used to adjust penetration P either by pushing the
butt end of the insert farther into the shaft or by hooking the tip
end of the shaft insert 16 and pulling the shaft insert out of the
shaft. Alternatively, a threaded adjuster 22 as shown in FIG. 18
can be used. Numbered gradations or color-coded stripes may be
placed along the length of either adjuster as an aid in making
repeat settings. This is particularly useful when using the
threaded adjuster 22 which is inserted until it contacts the stop
24.
[0078] The shaft insert 16 of this invention can be inserted before
or after a grip has been installed on a shaft or club. If a grip is
in place, e.g. when retrofitting existing clubs, as shown in FIG.
2a, the air hole in the standard size grip, which is normally about
0.15 inches in diameter, needs to be enlarged to about 0.55 inches.
This may be accomplished by use of a plug cutter (not shown). The
larger hole will allow insertion of the shaft insert 16 itself as
well as an insert adjuster 17 or 22, to make penetration
adjustments or to remove the shaft insert 16. Although not
necessary when a bonding agent has been used to attach the shaft
insert within a shaft, the grip plug 20 can be replaced and bonded
into its original position to assure that the club has been
rendered non-adjustable during play and thereby conforming to the
present Rules of Golf.
[0079] The maximum range of said penetration P possible with this
embodiment will depend in large part on the profile of the inner
surface of the golf shaft 10 and the size and shape of the shaft
insert 16. Materials hard enough to provide the range of stiffness
required for suitable shaft inserts will allow minimal compression,
so that retrofitting standard golf clubs may constrain the range of
penetration P due to the taper of the shaft. The range of
penetration can be increased with the use of a compressible
material placed between the two shafts as described in the
alternative embodiments.
[0080] In general the extent of penetration P of the shaft insert
into the shaft will range from about 1 to about 10 inches,
preferably about 2 to about 6 inches. Adjustment of the extent of
penetration P of the shaft insert changes the overall flex of the
shaft in the Toe and Swing Planes of the golf club and therefore
the club's dynamic swing parameters. For instance, as the
penetration of an 18-inch tubular aluminum shaft insert is varied
over a four-inch range, the overall shaft flex, as measured in
industry standard terms of frequency, changes approximately 7 CPM
(cycles per minute). The range of adjustment can be increased by an
additional 7 CPM by replacing the 18-inch insert cited above with a
24-inch insert. Thus starting with a golf club which has a 255 CPM
natural flex without any insert, and using either the 18-inch
aluminum insert or the 24-inch insert, a combined range of flexes
from 255 to 269 CPM can be spanned. This CPM range covers 90% of
the hundreds of golfers tested by the inventor using the
traditional trial and error fitting methods to find the best flex
for each player. Other higher strength-to-weight ratio materials
can be used to form the shaft inserts, e.g. graphite, aluminum, or
titanium. These materials will increase the range of a single
insert length and are within the scope of this invention. An insert
can only increase the overall stiffness of a golf shaft. It cannot
decrease the stiffness below the original stiffness of the
shaft.
[0081] As the amount of penetration P of the shaft insert 16 is
increased, the overall flex of the golf club shaft increases due to
increased stiffness caused by the presence of the shaft insert 16
as it moves from an initial position mostly under the grip 12
farther into the middle portion of the golf club shaft 10 where
bending of the shaft increases during a swing. When the golf club
shaft 10 is not bent (as shown in FIG. 2a), there is little effect
from the presence of the shaft insert. But during the swing of a
club, the shaft typically bends a total of about three inches over
its entire length, which affords the shaft insert 16 an opportunity
to change the overall stiffness of the shaft. As best seen in FIG.
2b, during a swing three sections of the shaft insert contact the
main shaft. The stiffness changes incrementally proportional to the
extent of bending of the golf club shaft 10. Three forces are
applied in different locations within the club shaft--a grip end
force 31, a central shaft insert force 32, and a club end force 33.
The central shaft insert force 32 is exerted in the direction of
the club bending. The grip end force 31 and club end force 33 are
exerted in the opposite direction.
[0082] The forces are constantly changing planes during a golf
swing due to the changing direction of bending of the club as shown
in FIG. 2c. At the address, very little bending occurs, but as soon
as the club is drawn back, the shaft bends away from the target but
remains relatively straight in the toe plane. At the top of a
swing, most of the bending is in the toe plane and the swing plane
bending is minimal. A result of the constantly changing positions
of the forces 31, 32, and 33 and their absolute values result in a
non-linear stiffening of the overall flex. The changing flex is not
as important, however, as the average value of the flex since the
flex is what determines the phase angle of flexing at the time of
ball contact.
[0083] Although there is little agreement over the role played by
the flexing of the shaft during a swing of a golf club, most
experts agree that there is one best flex for each player. This
inventor believes that one flex works best for each player, but is
a different numerical value for each shaft type, grip, club head
design and swing weight. The enormous number of combinations of
these variables is so great that it is nearly impossible for club
fitters to build optimum clubs no matter what calculations are
performed before construction. Thus the inventor advocates finding
the best flex for each player for each individual club. This
results in each shaft delivering the club head to the ball at the
best attitude and phase angle of the various oscillations occurring
in the Swing Plane, Toe Plane and Torque Axis of the specific
player. Thus the ball is struck solidly or at least in a manner to
compensate for the errors in that player's average swing path and
timing. Most preferably, the adjustment of the flex of a club is
performed after the club has been assembled as this technique
provides an opportunity to compensate for all the variables in a
practical manner.
[0084] For maximum energy transfer and therefore the longest shots,
the center of gravity of the club head should strike the ball. But
for straighter shots for a golfer with an average swing, it may be
better for ball contact to occur slightly off-center to compensate
for player-induced errors in the swing plane or torque deflection
errors caused by club head and shaft characteristics. Although hard
to fix in practice, player-induced errors are easy to identify
using photography. Errors in directional control due to shaft
oscillation phase angle are much more difficult to measure. When
shaft flex oscillation in the Swing, Toe and Torque Planes are
measured during player swings using strain gauges mechanically
attached to the shaft and electrically connected to a computer, and
the waveforms recorded. During a typical swing, the shaft bends
around 3 inches in all directions through 1.25 cycles of its flex
frequency, in both the Swing and Toe Plane, both axes having the
same flex frequency. The Torque Plane features an oscillation that
is independent of the other two flex frequencies and is three to
four times higher, 3.75 to 5 cycles, depending on the shaft model,
with an amplitude of a few degrees of angle. All three axes can
have different phase angles at ball contact, varying from swing to
swing for the same player, and varying more from player to player.
The Toe Plane phase angle predominantly determines where on the
club head the ball is struck, and the Swing Plane and Torque Plane
phase angles determine the aiming direction of the club head at
contact.
[0085] For example, if the club head is slightly open at ball
contact due to player-induced Swing Plane error and Torque
oscillation combined, which would cause the ball to go to the right
of the target, then striking the ball off-center near the toe of
the club face is best, since that will bring the ball back toward
the target line. This is known as the gear effect due to
right-to-left spin imparted from such contact, the latter of which
being well known in the art. The net result of all these errors,
without identifying the extent of any of them, is that some errors
will cancel each other and cannot be predicted in their net effect,
which is required to build optimized clubs with fixed parameters.
The best compromise of each player's swing idiosyncrasies and club
design parameters can only be found by adjusting the flex after
club manufacture in order to adjust shaft deflection incrementally
in the Toe Plane. This has the effect of determining where the ball
strikes the club head, which the inventor believes allows fine
tuning of directional control for most players. This concept runs
counter to almost all that is written and most likely believed by
experts who teach golf and design golf equipment, but is the crux
of this invention.
[0086] It is not necessary to know anything about a player's
ability to equip him or her with clubs that the player can adjust
to optimize his ability to hit shots directed at a target. This is
particularly true with the driver, but extends through the irons
and surprisingly, includes the putter. Good players know that there
is an optimum flex for a putter and have usually found it
experimentally by trying hundreds of putters. But the average
player is not aware of this, and if he were, would have only
limited opportunity to experiment. This invention allows a player
to try a large number of flexes un-supervised, to discover the best
flex for each of his clubs individually, and then to stop adjusting
them whenever he sees fit, and attach the shaft inserts in proper
place to make the club legal under USGA Rules. ps Use of Added
Joining Agent
[0087] Several alternative joining agent embodiments are shown in
FIG. 7 through FIG. 15, each with the addition of a compressible
material which provides friction and holding power between the two
shafts while allowing greater depth of penetration for tapered
shafts. The joining agents are shown as being added to a tubular
shaft insert embodiment but are equally useful with the solid cross
section shaft insert embodiment of FIG. 5a.
[0088] The maximum possible penetration for a shaft insert depends
on the inside diameter of the golf club shaft 10, the outer
diameter and length of the shaft insert 16, the relative tapers of
both shafts, and the compressibility of the added joining agent 18.
These factors also limit the range of flex adjustments possible for
any single insert. To increase the range of flexes, shaft inserts
of different materials, flexes, and lengths can also be used. Once
an adjustment is made, it will remain for many rounds of golf,
particularly when there is an added joining agent 18 present in the
system.
[0089] A first joining agent configuration is shown in FIGS. 7 and
8. In FIG. 7, the joining agent 18 is a sleeve which fits over the
shaft insert 16 while still having an outer diameter small enough
to fit within the cavity of the golf club shaft 10. The sleeve is a
compressible material that fits between the shaft and the shaft
insert. It is not joined to either and is shown in the drawings as
a scalloped surface.
[0090] A second variation of joining agent 18 is shown in FIGS. 9
and 10. This is the most preferred joining agent, particularly for
finally locating a shaft insert within a shaft. It entails placing
a coating of a compressible adhesive material around a portion of
the shaft insert 16 so that upon curing of the adhesive material,
the shaft insert becomes bonded into place. A silicone adhesive,
such as GE Silicone.TM., is a suitable material. It has the
desirable properties of bonding to the shaft insert 16, providing
friction to the golf club shaft 10, a large degree of
compressibility, and long life expectancy. Since it is bonded to
one surface, it may be superior to the previous alternative in
terms of handling convenience.
[0091] A third alternative embodiment reverses the location of the
bonding of said joining agent 18 from the outer surface of said
insert 16 to the inner surface of said golf club shaft 10 shown in
FIGS. 11 and 12. There may be manufacturing disadvantages to this
arrangement.
[0092] A fourth alternative embodiment of the invention adds the
joining agent to two surfaces: a thin coating of a compressible
material adhering to both the insert and the outer shaft as shown
in FIGS. 13 and 14. The insert is held in place by friction between
the two joining agents. This configuration may provide a maximum
range of penetration and maximum friction.
[0093] The fifth alternative embodiment of the invention, shown in
FIG. 15, employs small pockets of said joining agent 18 spaced over
the length of the insert instead of covering the entire length. The
holding power of each setting may be somewhat diminished compared
to the previous alternatives, but performance is comparable to the
other choices, and it is the least costly to manufacture.
[0094] A useful variation of this embodiment, shown in FIG. 19,
employs small pockets of joining agent, of ever increasing
diameters progressing from the tip to the butt end of the insert.
The largest diameter to fit inside the golf club shaft would be the
last left on the insert, the other larger diameters of the joining
agent to be removed by the club fitter or player before final
assembly. This configuration provides a universal insert size for
use in golf shafts of varying diameters.
[0095] The sixth alternative method of ad Listing and holding the
shaft insert 16 in place is shown in FIG. 16 and 17. Shaft insert
16 has a spiral length of wire wrapped around it and bonded to it
to form self-tapping threads 26. Female threads are impressed in
the thread holding agent 28 by rotation of said self-tapping
threads 26. Torquer 30 provides a means to twist the shaft insert
using, for instance, a standard Philips head screwdriver. Said
thread holding agent 28 is applied to the inner surface of said
golf club shaft 10 and must be pliable enough to allow the
self-tapping threads to penetrate it slightly and obtain a
purchase. Alternatively, but not shown, the position of the threads
and holding agents could be reversed with the threads bonded to
said golf club shaft 10 and said thread holding agent 28 bonded to
said shaft insert 16.
[0096] Once in place, the threaded shaft insert is held in place
until a new position is obtained by rotation of the insert, the
amount of rotation determining the degree of insertion like any
standard screw-driven device. The operation of a golf club fitted
with this alternative embodiment is similar to the embodiment
described earlier.
[0097] Fixed Flex Configuration
[0098] This alternative method for finding and adjusting the flex
of a golf club, not shown in any of the figures, uses one of the
embodiments described or any other suitable method to determine the
optimum flex setting for a specific player for the specific club
parts to be used to build a custom club for that player. After the
flex setting is measured numerically on a frequency analyzer common
in the golf club industry, the adjustable shaft insert can be
replaced by a non-adjustable insert that is permanently bonded in
whatever position that yields the same flex reading.
[0099] Alternatively, a shaft insert bonded in place could be used
to stiffen any shaft to any target flex, however that target flex
is determined, by the method described above or by any other
flex-fitting methods, of which there are many in use by custom club
fitters and amateurs alike.
[0100] Once inserted and bonded in place, a shaft insert will
forever change the original flex of the club to the target flex.
The balance of a set of clubs can then be "tuned" to that target
flex by proper placement of a shaft insert of this invention. For
the average golfer this will enable all of the clubs in his set to
feel and swing the same. This will also insure that the adjustment
would not drift from its predetermined setting. Moreover, a
standard grip can be used to hide the existence of the shaft
insert.
[0101] For a professional golfer and those with very low handicaps,
the ability to individually control the flex of each club using the
adjustable shaft inserts will generally be preferred.
[0102] The present invention allows the building of partially
finished clubs with a variety of flexes starting with only a few
flexes and then altering them with non-adjustable inserts. This
would lower the cost of manufacturing and stocking many different
flexes, as is the present industry practice. Clubs could be
pre-assembled with fewer flexes and later adjusted, perhaps even
while the customer waits, by using quick setting bonding
agents.
[0103] Accordingly, it can be seen that locating a movable
stiffening device inside a golf shaft is the most effective and
cosmetically desirable method for adjusting the flex of a golf club
during experiments, practice, and play. The shaft insert can be
made a permanent part of a club and thereby legal for play under
U.S.G.A. Rules.
EXAMPLE 1
[0104] The distance and scatter of shots from a single player using
a driver with no shaft insert is shown in FIG. 20a. The distance
and scatter of shots from the same player using the same driver but
with a 14 inch shaft insert in accordance with FIG. 1 but varying
the amount of penetration P in the club is shown in FIG. 20b. Each
dot represents a single shot measured in distance with a radar gun
with estimated 2% accuracy and left or right track by less accurate
visual estimation from the tee. The diameters drawn are the
weighted average of 80% of shots. The crosses at the center
represent average distance of each sample. As shown, with no shaft
insert (FIG. 20a) the player aver-aged 240 yards, but with a broad
scatter of 30 yards. With the addition of the insert at the very
beginning of the butt end of the shaft, the yardage dropped about 8
yards, but the scatter became less--thus a more repetitive
performance from shot to shot with the same club. And as the shaft
insert was moved farther into the shaft, the yardage increased and
the scatter was reduced until a maximum of performance was reached
for this player and this shaft insert when the shaft insert depth
was 3". When the depth was increased to 4", performance (both
distance and scatter) worsened.
[0105] These results demonstrate that the presence of a shaft
insert at the ideal location for this player reduced distance by
only 2 yards (less than 1%). However, the shot cluster improvement
(reduction in scatter) was 100%, going from an initial 30 yards to
only 15 yards.
[0106] While these results were obtained using a radar gun, they
are identical to those obtained for the same player on a trial and
error basis without a radar gun. Thus players can find their own
best setting while practicing and then once the setting is found,
the shaft insert can be permanently bonded in place to produce a
club which is approved for use by the U.S. Golf Association.
[0107] Although the description above contains much specificity,
these should not be construed as limiting the scope of the
invention but as merely providing illustrations of some of the
presently envisioned embodiments of this invention. Various other
embodiments and ramifications that would occur to a workman in the
field are possible within its scope. The scope of this invention is
determined by the appended claims and their legal equivalents,
rather than by the description and example given.
* * * * *