U.S. patent application number 10/532015 was filed with the patent office on 2006-01-12 for putter heads.
Invention is credited to Norman Matheson Lindsay.
Application Number | 20060009305 10/532015 |
Document ID | / |
Family ID | 9946207 |
Filed Date | 2006-01-12 |
United States Patent
Application |
20060009305 |
Kind Code |
A1 |
Lindsay; Norman Matheson |
January 12, 2006 |
Putter heads
Abstract
A putter-head (1) giving positive ball-topspin (S) for
impact-heights (h.sub.i) above 5 mm from its sole (6), has its
center of mass (9) located p mm behind its impact face (8) at
height h.sub.c mm above the sole (6), a mass M kgm and a radius of
gyration K mm about the heel-toe axis (4-5) through the center of
mass (9). The loft (.alpha.) of the impact face (8) increases
monotonically with height from 5 to 15 mm above the sole (6), where
(K.sup.2/p) is greater than 5 mm and S=S.sub.G+S.sub.L where
S.sub.G and S.sub.L are percentage spin rates based on:
S.sub.G=(250.times.h)/[(3.2+70.times.M).times.(K.sup.2/p)+p]
S.sub.L=(-0.76.times..alpha..sub.i)/[1+0.04.times.(p/K).sup.2] for
which: h=h.sub.i-h.sub.c-p.times.sin(a.sub.i) and .alpha..sub.i
degrees is impact-face loft at height h.sub.i. From the sole (6)
upwards, the impact face curves (16) from negative- to
positive-loft and merges into an upper flat-portion (15) of
positive loft. Alternatively, it has upper and lower flat-portions
(21, 22) of positive- and negative-loft respectively. A hosel (30,
31) gives high compliance at impact for head-rotation relative to
the shaft (33) about the heel-toe axis (4-5), and allows choice of
lie in shaft-attachment.
Inventors: |
Lindsay; Norman Matheson;
(Buckinghamshire, GB) |
Correspondence
Address: |
DAVIS & BUJOLD, P.L.L.C.
FOURTH FLOOR
500 N. COMMERCIAL STREET
MANCHESTER
NH
03101-1151
US
|
Family ID: |
9946207 |
Appl. No.: |
10/532015 |
Filed: |
October 21, 2003 |
PCT Filed: |
October 21, 2003 |
PCT NO: |
PCT/GB03/04543 |
371 Date: |
April 20, 2005 |
Current U.S.
Class: |
473/313 ;
473/330; 473/340 |
Current CPC
Class: |
A63B 53/023 20200801;
A63B 53/0441 20200801; A63B 60/00 20151001; A63B 53/0487 20130101;
A63B 53/007 20130101; A63B 53/0408 20200801 |
Class at
Publication: |
473/313 ;
473/340; 473/330 |
International
Class: |
A63B 53/02 20060101
A63B053/02; A63B 53/04 20060101 A63B053/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 21, 2002 |
GB |
0224356.6 |
Claims
1-20. (canceled)
21. A putter-head for imparting a positive rate (S) of topspin on a
golf ball for impacts with the ball throughout a range of impact
height (h.sub.i) extending above 5 millimeter from the bottom of
the putter-head, wherein the head has a center of mass located at a
distance p millimeter behind its impact face and a height h.sub.c
millimeter above the bottom of the head, a mass M kilogram and a
radius of gyration K millimeter about the heel-toe axis through the
center of mass, and the loft (.alpha.) of the impact face increases
monotonically with height from 5 to 15 millimeter above the bottom
of the putter-head, and wherein: K.sup.2/p>5 (a) and
S=S.sub.G+S.sub.L (b) where the spin rates S.sub.G and S.sub.L
expressed as percentages, are as follows:
S.sub.G=(250.times.h)/[(3.2+70.times.m).times.(K.sup.2/p)+p]
S.sub.L=(-0.76.times..alpha..sub.i)/[1+0.04.times.(p/K).sup.2] for
which: h=h.sub.i-h.sub.c-p.times.sin(.alpha..sub.i) and
.alpha..sub.i degrees is the impact-face loft at height h.sub.i
millimeter.
22. The putter-head according to claim 21, wherein the loft
(.alpha..sub.15) at 15 millimeter above the bottom of the head is
at least 3 degrees larger than the loft (.alpha..sub.5) at 5
millimeter above the bottom of the head.
23. The putter-head according to claim 22, wherein .alpha..sub.15
is at least 5 degrees larger than .alpha..sub.5.
24. The putter-head according to claim 23, wherein .alpha..sub.15
is at least 7 degrees larger than .alpha..sub.5.
25. The putter-head according to claim 21, wherein S is at least
+2.5%.
26. The putter-head according to claim 25, wherein S is at least
+5.0%.
27. The putter-head according to claim 21, wherein the head also
imparts a positive rate (S) of topspin of at least 5.0% for impacts
with the ball throughout a range of impact height (h.sub.i)
extending above 2.5 millimeter from the bottom of the
putter-head.
28. The putter-head according to claim 21, wherein h.sub.c is less
than 10 millimeter.
29. The putter-head according to claim 28, wherein h.sub.c is not
more than 7 millimeter.
30. The putter-head according to claim 21, wherein the ratio
K.sup.2/p is more than 5 millimeter.
31. The putter-head according to claim 30, wherein the ratio
K.sup.2/p is not less than 8 millimeter.
32. The putter-head according to claim 31, wherein p is at least 10
millimeter.
33. The putter-head according to claim 32, wherein p is less than
35 millimeter.
34. The putter-head according to claim 33, wherein p is less than
30 millimeter.
35. The putter-head according to claim 21, including
shaft-attachment means and wherein a putter-shaft is attached to
the head via the shaft-attachment means and the horizontal offset
of the axis of the shaft from the heel-toe axis is less than the
radius of the shaft at the shaft-attachment means.
36. The putter-head according to claim 35, wherein the
shaft-attachment means has zero horizontal offset from the heel-toe
axis.
37. The putter-head according to claim 35, wherein the horizontal
displacement of the shaft-attachment means from the center of mass
is less than the radius of gyration K.
38. The putter-head according to claim 21, wherein the impact face
includes an upper, flat portion having positive loft.
39. The putter-head according to claim 21, wherein the impact face
includes a lower portion which is curved and has loft that
increases from a negative value to a positive value upwardly from
the bottom of the head.
40. The putter-head according to claim 21, wherein the impact face
includes a lower, flat portion having negative loft.
Description
[0001] This invention relates to putter-heads and is concerned
especially with putter-heads for imparting topspin to a golf ball
at impact.
[0002] In putting a golf ball, it is desirable to impart forward
rolling spin or topspin to the ball during the putting stroke.
Topspin reduces ball skid on the putting surface and helps to
initiate pure rolling motion. Imparted topspin is defined as the
component of ball spin about a horizontal axis parallel to the
putter impact-face imparted at impact by a putter such that the
ball peripheral speed on the top surface of the ball exceeds its
linear or translational speed.
[0003] It is known that putters with negative face-loft normally
hit above the horizontal equator of a golf ball and thus tend to
impart topspin. However, this type of impact disadvantageously
forces the ball downwards and into the putting surface, causing
erratic loss of launch energy, especially on soft putting
greens.
[0004] Thus, it is preferable that the impact point on the ball is
below its equator, which generally ensures that the ball lifts off
the putting surface at impact. Impacts just above the horizontal
equator of the ball are also acceptable, especially if combined
with an upward putter-head trajectory as this ensures that the
downward component of impact force is a small fraction of the total
and so has negligible deleterious-effect on the putt.
[0005] It is one of the objects of the present invention to provide
an improved putter-head for imparting topspin to a golf ball at
impact.
[0006] According to the present invention there is provided a
putter-head for imparting a positive rate (S) of topspin on a golf
ball for impacts with the ball throughout a range of impact height
(h.sub.i) extending above 5 millimetre from the bottom of the
putter-head, wherein the head has a centre of mass located at a
distance p millimetre behind its impact face and a height h.sub.c
millimetre above the bottom of the head, a mass M kilogram and a
radius of gyration K millimetre about the heel-toe axis through the
centre of mass, and the loft (a) of the impact face increases
monotonically with height from 5 to 15 millimetre above the bottom
of the putter-head, and wherein: K.sup.2/p>5 (a) and
S=S.sub.G+S.sub.L (b)
[0007] where the spin rates S.sub.G and S.sub.L expressed as
percentages, are as follows:
S.sub.G=(250.times.h)/[(3.2+70.times.M).times.(K.sup.2/p)+p]
S.sub.L=(-0.76.times..alpha..sub.i)/[1+0.04.times.(p/K).sup.2] for
which: h=h.sub.i-h.sub.c-p.times.sin(.alpha..sub.i)
[0008] and
[0009] .alpha..sub.i degrees is the impact-face loft at height
h.sub.i millimetre.
[0010] The loft (.alpha..sub.15) at 15 millimetre above the bottom
of the head may be at least 3 degrees larger than the loft
(.alpha..sub.5) at 5 millimetre above the bottom of the head, but
is preferably at least 5 degrees or more especially, 7 degrees,
larger.
[0011] The minimum value of rate S of topspin may be at least +2.5%
or, more preferably, +5.0% for values of h.sub.i above 5 millimetre
from the bottom of the putter-head. For values of h.sub.i down to
2.5 millimetre, the minimum spin rate S is preferably +5.0%. For
preference, the height h.sub.c may be less than 10 millimetre, or,
more preferably, not more than 7 millimetre, and the value of
(K.sup.2/p) may for preference be not less than 5 or, more
especially, 8 millimetre. The distance p is preferably at least 10
millimetre and less than 35 millimetre but more preferably less
than 30 millimetre.
[0012] For preference a putter-head according to the invention is
provided with shaft attachment means that provides additional
compliance to rotation of the head of up to .+-.0.5 degrees
relative to the shaft to enable achievement of vertical gear
effect. Head rotation about the heel-toe axis may also be increased
by arranging that stiffness of the shaft where it attaches to the
putter-head is minimised. This is achieved by ensuring that the
shaft deformation during impact is predominately in bending or
twisting mode rather than in axial compression or elongation mode.
Thus for preference, a putter-head according to the invention may
be provided with shaft attachment means wherein the axis of the
shaft-attachment means is horizontally displaced d millimetre
either side of the horizontal heel-toe axis through the centre of
mass. To optimise the imparted topspin properties of the assembled
putter, d should be ideally zero or less than r, where r is the
radius of the putter shaft at the shaft-attachment means. It is
also advantageous for the horizontal displacement (measured in any
direction) of the shaft-attachment means from the centre of mass of
the putter-head to be less than the radius of gyration K.
Putter-heads in accordance with the present invention will now be
described, by way of example, with reference to the accompanying
drawings, in which:
[0013] FIGS. 1 to 3 are front-elevation, rear-elevation and plan
view respectively of a first putter-head according to the
invention;
[0014] FIG. 4 is a sectional side-elevation of the first
putter-head taken on the line IV-IV of FIG. 3;
[0015] FIG. 5 is a perspective view from the rear of the first
putter-head;
[0016] FIGS. 6a and 6b are, respectively, diagrammatic views of the
centre section of the first putter-head and a golf ball at impact,
in two different circumstances;
[0017] FIG. 7 is a sectional side-elevation of a second putter-head
according to the invention;
[0018] FIG. 8 is illustrative of a form of hosel that may be used
in the putter-heads of FIGS. 1 to 5 and FIG. 7;
[0019] FIGS. 9a and 9b are, respectively, sectional views of use of
the hosel of FIG. 8 in providing two different angles of lie of the
putter-shaft; and
[0020] FIG. 10 is in further illustration of a feature of the hosel
of FIG. 8.
[0021] Referring to FIGS. 1 to 5, the putter-head 1, comprises an
impact-face flange 2 and a base 3. The base 3, which forms the
major part of the putter-head 1, defines the heel 4, the toe 5 and
the sole 6 of the head 1, and incorporates a shaft-hosel 7. The
flange 2 is of an unusually thin section for a putter-head, being
for example of 4 millimetre or less in thickness, yet establishes a
rigid interface between the impact face 8 and the base 3. This
rigidity is important in ensuring that impacts on the middle or
upper part of the face 8 do not deflect the flange 2 relative to
the base 3, but instead rotate the entire head 1 fully about its
centre of mass 9. This in turn ensures that the putter-head 1
behaves as a rigid body during impact, and parameters such as
imparted ball spin and velocity are accurately predictable and
fully achieved.
[0022] In one construction of the putter-head 1 of FIGS. 1 to 5,
the desired rigidity and mass properties are realised by casting it
of 316 stainless steel or a similar alloy. In an alternative
construction, the impact flange 2 is provided as a separate part of
titanium, aluminium or magnesium alloy or of a high modulus
composite. The main requirement is that the flange 2 has a mass
which is a small proportion of the overall mass of the putter-head
1, yet provides a rigid interface between the golf ball and the
base 3 at impact. This allows-the centre of mass 9 to be positioned
close to the bottom surface or sole 6, and some distance from the
face 8. The height h, of centre of mass 9 above the sole 6 is
preferably less than 10 millimetre or, more preferably, not more
than 7 millimetre since this limits the amount of negative loft
required.
[0023] A very high value of p, the distance of centre of mass 9
behind the impact face 8, produces high sidespin and directional
errors under offset impacts. This undesirable characteristic can be
reduced by increasing the moment of inertia of the head 1 about the
vertical axis, but increase of this moment affects playing control
and/or requires the mass of the head 1 to be excessive. As a
result, it is preferable to limit the distance p to be less than 35
millimetre, but, more preferably, less than 30 millimetre. Small
values of p are disadvantageous in putter-heads of the present
invention since they severely limit vertical gear effect, and
accordingly, it is preferred to adopt a construction for which p is
at least 10 millimetre.
[0024] By way of modification of the putter-head of FIGS. 1 to 5,
the impact face 8 may be formed by material which is softer than
that of the flange 2 and which is provided as a layer, or as an
insert, bonded to the flange 2 for reducing vibration and noise
intensity (so as to give a so-called `soft-feel`). However, it is
disadvantageous to have the entire structure of the flange 2 in
soft material as this reduces topspin imparted by vertical
gear-effect.
[0025] The putter-head of FIGS. 1 to 5 and its action will now be
described in further detail with reference to FIGS. 6a and 6b which
are, respectively, diagrammatic representations of the centre
section of the putter-head 1 at the instant of impact with a golf
ball 13 resting on a putting surface 14, in two different
circumstances.
[0026] As illustrated in exaggerated form in FIGS. 6a and 6b, the
impact face 8 of the putter-head 1 is of curved profile
transversely of the heel-toe axis only, and has a lower, curved
half 15 that has a loft angle .alpha. degrees which increases with
increase in height, progressively from a negative value at the sole
6, through zero to a positive value .alpha..sub.MAX where it merges
into the upper half 16 of the face 8. The upper half 16 is flat and
has a loft angle of .alpha..sub.MAX so as to be tangential to the
lower half 15 where they merge; accordingly, the loft of the impact
face 8 increases monotonically throughout its full height upwardly
from the sole 6.
[0027] As represented only in FIG. 6a, the centre of mass 9 of the
putter-head 1 is located at distance p millimetre behind the impact
face 8 and at a height h.sub.c millimetre above the sole 6. The
centre of impact of the face 8 with the ball 13 (which is a playing
variable with random error) is shown as occurring at height ha
above the sole 6 in the circumstances of FIG. 6a but at height
h.sub.b in the circumstances of FIG. 6b.
[0028] The main effect required of the impact is to launch the golf
ball 13 with linear velocity substantially along the intended line
of putt and preferably with a slight positive (upward) elevation
angle. The upward trajectory is often provided by a small amount of
loft (typically +3 degrees) on the impact-face of a putter.
Moreover, most golfers adopt an approximate `pendulum swing` in
putting, in which the putter-head is swung about a substantially
horizontal axis with the swing rotation axis and the putter shaft
axis in (or nearly so) a common plane that is substantially
parallel to the heel-toe axis of the putter-head. The main variable
with this type of swing is the position of the ball in relation to
the vertical arc followed by the putter-head. For preference,
impact with the ball occurs at or just beyond the bottom of the arc
(on the upward part of the arc), but in practice may occur before
or later than this.
[0029] In the circumstances represented in FIG. 6a, impact takes
place at the bottom of the arc, where the putter-head trajectory is
horizontal (shown by arrow 17a). Impact in such circumstances
generally occurs at mid-height, within the upper part 15 of the
impact face 8. The loft angle .alpha..sub.MAX applies provided the
clearance 18a between the putting surface 14 and the sole 6 is not
more than the radius of the ball 13 less the height of the curved
lower half 16 of the impact face 8. If the ground-to-sole clearance
18a is more than this, the height of contact will increase and may
disadvantageously rise above the horizontal equator of the ball 13
and consequently launch the ball 13 with a slight negative
elevation trajectory. This type of putting stroke is rare except
with players of less than moderate skill and typifies poor putter
control. Nevertheless it is preferred that excessive negative ball
trajectory is avoided by providing that the region on the
impact-face where the loft is negative is limited to the lower 12
millimetre, or more preferably the lower 9 millimetre.
[0030] FIG. 6b represents the circumstances in which impact occurs
at a point beyond the bottom of the pendulum arc where the
putter-head trajectory (depicted by arrow 17b) has positive
elevation. The ball launch trajectory in these circumstances is
dependent on the combination of trajectory elevation angle and the
loft angle at impact; the latter is generally slightly negative and
varies both with the ground clearance 18b and the elevation angle
of the trajectory 17b. Provided the sum of putter-head trajectory
angle and loft angle at impact point is greater than -20% of the
trajectory elevation angle, the ball launch elevation angle will be
positive.
[0031] Thus, the ball is still given a slight lift for impacts in
the lower (negative loft) region of the impact-face 8 provided the
bottom of the pendulum arc is kept low as before.
[0032] The aim of the present invention is to provide a putter-head
that imparts topspin on the ball from all pendulum-swing putts but
also provides high probability of imparting positive lift on the
ball at impact.
[0033] It is known that two mechanisms impart spin with
club-on-ball impact in golf, namely eccentric impact, commonly
known as `gear-effect`, and oblique impact which is most commonly
experienced as backspin due to club-face loft. The gear-effect
realised with a putter-head is dependent on the condition that the
line of impact (that is, the line normal to the impact surfaces at
the point of impact) is offset from the centre of mass of the head.
It follows that the condition for gear-effect with the putter-head
of the present invention is also dependent on the loft angle of the
impact face at the point of impact.
[0034] The offset distance h between the line of impact and the
centre of mass 9 is given by:
h=h.sub.i-h.sub.c-p.times.sin(.alpha..sub.i) (1)
[0035] where h.sub.c and h.sub.i are, respectively, the height
(millimetre) of the centre of mass 9 and the impact point above the
bottom-most part, the sole 6, of the putter-head, and .alpha..sub.i
(degrees) is the loft angle of the putter face 8 at the point of
impact (positive for upward tilt).
[0036] The value of spin attainable with gear-effect is known from
Newtonian dynamics assuming that the putter-head and golf ball
behave as free rigid bodies at impact, and is given, as a
percentage, by:
S.sub.G=(250.times.h)/[(3.2+70.times.M).times.(K.sup.2/p)+p] (2)
where M is the putter-head mass (kilogram), K is the radius of
gyration for rotation about the horizontal heel-toe axis through
the centre of mass (millimetre) and S.sub.G is the ratio (expressed
as a percentage) of the peripheral velocity of the ball due to
rotation, to its linear or translational velocity.
[0037] It is found that S.sub.G is highly dependent on the term
(K.sup.2/p) in equation (2). A low value of this term, such as 5
(millimetre) gives a very high vertical gear effect, which in turn
requires high negative loft to overcome the tendency for backspin
at low impact heights. It is also the case that most conventional
putter-heads (especially low cost, one-piece cast heads) have
values of (K.sup.2/p) of 10 to 20 or so, and golfers are familiar
and more attuned to this weight distribution. It is thus an aim
with the putter-head of the invention to arrange that (K.sup.2/p)
is at least more than 5 millimetre, but preferably 8 millimetres or
more.
[0038] Further, golfers are not used to putters having very low
inertia about the heel-toe axis (or about any other axis). Such
low-inertia putters can feel less `solid` to play with, which is
disadvantageous.
[0039] It is accordingly preferable that the value of the heel-toe
inertia, namely, (M.times.K.sup.2), is not less than 25
kilogram-millimetres.sup.2 or, more preferably, is greater than 30
kilogram-millimetres.sup.2.
[0040] For vertical gear effect to impart topspin rather than
backspin, the value of h must be positive. This is exemplified in
FIG. 6a where the line of impact 19a (collinear with the centre of
the ball 13 and the impact point) passes above the centre of mass
9.
[0041] With pendulum-swing putts the putter-head elevation
trajectory is always parallel to the sole 6 and therefore the spin
imparted due to oblique impact is a function of the impact-face
loft .alpha..sub.i but not trajectory, and is given by:
S.sub.L=(-0.76.times..alpha..sub.i)/[1+0.04.times.(p/K).sup.2]
[0042] where S.sub.L denotes the spin ratio (expressed as a
percentage and defined as for S.sub.G) as a function of loft. It is
to be noted that positive loft imparts negative spin or backspin
and negative loft imparts topspin.
[0043] Conveniently, it is practical to provide negative loft,
which in turn imparts topspin, in the lower half 16 of the
impact-face 8 and this compensates for the fact that the height h
defined in equation (1) normally becomes negative for small values
of hi. This is depicted in FIG. 6b where the line of impact 19b is
shown to pass below the centre of mass 9.
[0044] The value of height h can in practice be kept positive even
for zero impact-height h.sub.i by arranging that:
h.sub.c-p.times.sin(.alpha..sub.i)
[0045] remains positive. However, this option requires severely
negative loft, especially for smaller values of distance p and thus
undesirably imparts negative ball-launch trajectory rather than the
desired lift. It is thus much more preferable to arrange that the
sum of S.sub.L and S.sub.G is positive at least for putts above the
lower limit of useful impact height, for example above 5
millimetres or 2.5 millimetres. It is preferable that the minimum
spin rate is +2.5%, or more preferably +5.0%, above 5 millimetres,
but below this down to 2.5 millimetres, it is very desirably
+5.0%.
[0046] Since the diameter of the impact footprint (that is, the
contact deformation area) is usually at least 5 millimetres (except
for very low-velocity putts), impacts at heights below 2.5
millimetres encroach onto the lower lip of the impact face. In
these circumstances, an impact will `top` the ball, giving abundant
topspin but at the expense of erratic length and direction
control.
[0047] It can be seen from equations (1) to (3) that a number of
putter-head parameters determine spin rate, namely p, h.sub.c, M, K
and .alpha..sub.i (which is a function of impact height). Typical
value ranges of these parameters for blade-style putters according
to the invention, are given in Table I. TABLE-US-00001 TABLE I p 10
to 18 millimetres h.sub.c 6 to 10 millimetres M 0.31 to 0.36
kilogram K 10 to 13 millimetres
[0048] For mallet-style putters the values for distance p and
radius of gyration K are generally larger than those for
blade-style putters. Table II below gives an example of a
putter-head based on FIGS. 1 to 5. TABLE-US-00002 TABLE II h.sub.i
.alpha..sub.i S.sub.G S.sub.L S.sub.G + S.sub.L (mm) (deg) (%) (%)
(%) 2.5 -7.5 -2.4 +5.3 +2.9 5 -5.0 -0.5 +3.5 +3.0 12 +2.0 4.9 -1.4
+3.5 p = 16 millimetres h.sub.c = 6.8 millimetres M = 0.32 kilogram
K = 11.6 millimetres .alpha..sub.MAX = 2.0 degrees (h.sub.i > 12
millimetres)
[0049] It is found in practice that the position of the shaft hosel
7 has a strong influence on the putter-head rotation about the
heel-toe axis during the very short duration of impact (less than
one millisecond). It has been found experimentally that if distance
d is the horizontal offset between the shaft attachment axis and
the heel-toe axis, topspin performance is enhanced when d is zero
and that increasing d reduces the imparted topspin. In order to
optimise the imparted topspin properties of the assembled putter, d
should be ideally zero, or, more generally, less than the radius r
of the putter-shaft.
[0050] A further advantage of positioning the shaft coupling close
to the centre of mass of the putter-head is that shaft vibrations
due to eccentric impact are minimised. In this respect, it is
advantageous that the axis of the means for attachment of the shaft
passes close (preferably not more than K millimetres) to the centre
of mass of the putter-head (as distinct from the heel-toe axis
through this centre).
[0051] FIG. 7 shows a sectional side-elevation of a putter-head 20
that is generally the same as the putter-head of FIGS. 1 to 5
except that the impact face in this case comprises an upper,
flat-face portion 21 and a lower, flat-face portion 22. The upper
portion 21 has typically zero or positive loft whereas the lower
portion 22 has negative loft; differences in loft-are exaggerated
in FIG. 7. The upper and lower portions 21 and 22 join one another
in a horizontal junction 23 (which is parallel to the heel-toe axis
and thus normal to the plane of FIG. 7). The loft angle of the
impact face accordingly changes abruptly at the junction 23, but
the effective loft actually experienced for impacts on or near the
junction 23 changes only gradually as the point of impact is moved
through the junction 23, owing to the softness of the cover
material of the ball. More particularly, the softness results in
the impact force being distributed above and below the junction 23
with the result that the effective loft tends to a value
intermediate the lofts of the two flat-face portions 21 and 22; the
junction 23 can be chamfered or rounded to enhance the
distribution. The change in loft may also be made more gradual by
reducing the hardness of the impact surface, for example by using
an elastomer insert instead of a steel face as depicted in FIG.
7.
[0052] FIG. 8 shows a sectional view of an alternative form of
hosel involving a male stub 30 and an annular recess 31 concentric
with it. The axis 32 of stub 30 is inclined at the desired lie
angle relative to the horizontal for attachment of the
putter-shaft. Attachment of the shaft is carried out by applying a
thixotropic adhesive within the hollow tip of the shaft and then
placing the shaft-tip over the stub 30 to locate within the
surrounding annular recess 31; the adhesive desirably has good
gap-filling properties and may, for example, be the `E3332` epoxy
adhesive sold under the registered trade mark PERMABOND. The recess
31 is typically only 2 to 3 millimetres deep and serves to centre
the shaft-tip relative to the stub 30.
[0053] The dimensions of the stub 30 and recess 31 are such that
the shaft can be fitted at different angles relative to the
concentric position so as to allow for different lie preferences.
This is illustrated by FIGS. 9a and 9b, FIG. 9a showing adoption of
an `upright` lie for shaft 33 on the stub 30 in which the shaft 33
is inclined at an angle of 78 degrees to the horizontal. FIG. 9b on
the other hand, shows adoption of a `flat` lie in which the shaft
33 is inclined at an angle of 66 degrees to the horizontal.
[0054] Referring again to FIG. 8, the seating plane at the bottom
of the annular recess 31 is shown by dashed line 34, and
intentionally not square to the axis 32 but is instead tilted
towards the horizontal so that the tip of the shaft 33 rests on
nominally one point on the plane containing line 34. This
arrangement is shown more clearly in FIG. 10 where the tip of shaft
33 touches line 34 at only one point 35. It is arranged that this
point 35 is located on the heel-toe axis 36.
[0055] At impact, the putter-head rotates about the heel-toe axis
36. This arrangement provides very high compliance to putter-head
rotation relative to the shaft 33 about the heel-toe axis 36 since
the rim of the shaft 33 is decoupled from the putter-head body via
the cured adhesive material of relatively low modulus, and the only
direct contact with the putter-head is at the one point 35 on the
axis 34 of rotation.
* * * * *