Note: Descriptions are shown in the official language in which they were submitted.
~he present invention relates to rackets, such
as tennis~ squash or badminton rackets or the like, which are
provided with tensioned s~ringing which forms the playing
surfaces of -Ihe racketsO
Such a racket basically comprises a handle or shaft
carrying a head in the form of an open marginal frame, for
example a generally oval or circular frame~ defining a
correspondingly shaped cen-tral openingO The tensioned stringing
extends back and forth across the central opening, and i~
composed of a first group of generall~ parallel string portions,
and a second group of generally parallel~string portions
extending generally perpendicular to, and interwoven with,
the string portions of the first group. The thickness of the
marginal frame between the opposite side surfaces thereof, in a
direction normal -to the plane of the stringing, is ~ ~ -
substantially ~reater than that oE the stringing. Such a
racket will hereinafter be referred to as "a racket of the
type specified".
In known rackets of the type specified, which are
currently commercially available and commor~1y u~ed~ -the
, , .
stringing passes through peripherallydistributed apertures
in the ~rame, the aperture~, at least at their ends which open
through the inner peripheral or inwardl~ facing surface of
the frame being located approximately centrally between the
~ opposite side surfaces. ~hus, the frame projects on opposite
sides of the single plane containing the stringing, and
therefore projects beyond both playing surfaces defined by
opposite sides of the ~tringing by a distance approximating
..
2 -
.
5~i~
one half of the wid-th of the frame in a direction normal to
said plane. The amount of the projection depends upon the
type and size of the racket1 and, for example, in a conv~tional
full size tennis racke-t, is of the order of ~" from said
plane~ When such a racket, which is s-t~ung centrally of its
frame, i5 used, anda player miss-hits a ball, and the ball
strikes the frame or the strings~'adjacent the frame, i.e.
plays a "wood" shot, the ball i~ deflected from its intended
traa~c-tory by the projecting frame, and the player usually
loses the point as a result.
In order to reduce the aforementioned disadvantage of
conventional centrally strung rackets, it has bee~ proposed
to provide a racket of the type specified, wherein the head
carries tensioned stringing which is disposed in two generally
parallel planes separated by a distance approx mating the
thickness of the frame.
~ hus, instead of the stringing, and therefore the playing
surfaces defined thereby, being recessed with respect to the
surrounding frame, the playing surfaces are generally flush with
the frame on opposite sides thereof. Since the projection of'
the frame relative to the playing surfaces is substantially
reduced, the unintentional de~lection of the ball, which occurs
when the eguivalent of a "wood" shot is played, i.e. when the
'ball strikes one or other playing surface directly adjacent
or in line with the frame, is reduced, and ball control
' maintained.
- 3 -
'
, , ~, .
However, the loading imposed on a "double~strung" frame
is approximately twice that imposed upon a conventional "sin~le-
strun~" or"centrally st~lng" frame, which gives rise -to
various problems and disadvantages. It is an object of the
present invention to provide an improved racket of th.e "double-
such
strung"type which avoids or substantially reduces/problems and
disadvan-tages~
~hus, from one aspect, the present invention consists
in a racket of the type specified wherein the head carries
tensxned stringing which is disposed in two generally
parallel planes separated by a distance approximating the
thickness of the frame~ the head including a structural
marginal frame part defining the central opening, and at
least one member.overlying and carried by.the structural
frame part, and being provided with means to position. said :
tensioned stringing in said two generally parallel, mutually
spaced planes~ .
. With this construction, it is unnecessary.to complicate
and/or weaken the structural frame part by providing it with
.
aper-tures or grooves for receiving and locating the stringin~,
20 . the apertures or grooves being, instead, formed in said at
.~ least one overlying member.
~he overlying member comprises a hard, substantially
incompressible elongate flexible str1p, for example of a
tough synthetic plastics material, which significantly
reinforces, and extends peripherally around a major
proportion of the outer peripheral surface of, the frame part;,
.
., . '
~50~
for example, at least from a position adjacent one side
of -the handle, around the frame part, to a position
adjacent the opposite side of the handle. Due to its
phys.ical characteristic~ and the fact that it is positively
secured to, or frictionally grips, the frame part, the strip
forms a lamination, significantly reinforcing the frame
part, whilst it is more compatible with the stringing than
the material of the frame part.
Although the structural frame part may be specially
made, or at least the outer peripheral surface thereof may
be specially adapted, to receive the flexible overlying
strip~ the strip may be designed to be fitted to the frame,
for example, the solid or tubular frame,of a conventional,
centrally strung metal racket.
Thus, from another aspect, the invention consists in.
a flexible strip arranged and a.dapted to be assembled
in overlying reIation, to the outer peripheral surface of
the head frame of a rac~et of the type specified, the strip
having a peripheral inner surface cooperable wlth the frame,
opposite side surfaces which are spaced apar~ by a distance
: approximating the thickness o~ the frame between the
opposi~e side surfaces of ~he latter, and having a length
such that, when assembled to the frame, the strip extends
around the frame for a major proportion of the peripheral
extent thereof, the strip being provided with means to
receive and locate tensioned stringing which is disposed
in two generally parallel planes separated by a distance
approximatin~ the thickness of 'he frame.
.. , ' , ~
... . .
,. . . . .................... . .
~, , . , . :
~he means for receiving and locating the stringing
may comI~ise apertures or grooves extending between~ ~n~
opening into, the opposite side surfaces o~ the stripO
Alternatively, said means may comprise projections on said
side surfaces around which the stringing is anchored.
The flexible strip just defined may be readily assembled
and secured to the existing frames of a conventional centrally
strung racket after removal of the central stringing thereof
and replacement or modification of the racket throat, withou~
modification and consequential weakening of the existing frame.
After assembly of the flexible strip, a strin~ing filament
; is threaded through the apertures, or laid in the groove, in
`the flexible strip, and passed back and forth across the
central opening, to produce the two sets of tensioned stringing
in the two generally parallel spaced planes.
~hus, from another aspect, the invention consists
in an accessory or conversion kit for converting a normally
centrally strung racket to double stringing, including a
- flexible strip as just defined, and a throat piece9 or
throat piece adaptor, provided with stringing-receiving
~ apertures dimensioned and arranged to locate the stringin~
:. .
disposed in said two planes~ and adap-ted to replace, or
adapt, the throat piece of the racket to be converted.
:
In order that the invention may be more readily
understood, reference will now be made to the accompanying
drawin6s, in which:
'..
'' '
'
, '
.. . . ... .
,, ;~, . ' : ' ' '
~igure 1 is a perspective view of a racket embodying
the pre~e~t invention;
Figure 2 is a section on the line 2-2 of Figure 1, on
an enlarged scale;
Figure 3 is a section on the line 3-3 of Figure 1, on
an enlarged scale;
Figure 4 is a fragmentary perspective view of the
overlying strip shown in Figure 2;
Figure 5 is a section, similar to that of Figure 2~ of
a modified head construction;
Figure 6 is a section similar to that of Figures 2 and
5~ showing the application of an overlying strip embodying
the invention to the existing metal frame of a conventionally
centrally strung racket, to convert the racket to double
stringin~; and ~-
~igure 7 is a plan view of a throat piece for use with
the~strip of Figure 6.
The racket shown in ~igure 1 ]may, for example, be a
.; Tennis racket which is basically formed, for example, moulded
or extruded, from a metal such as aluminium or steel, or
,
alloy thereo~.
: In particular, the racket includes a metal strip, for
~; 20 example an extruded aluminium strip, which is bent ~o that the
free end portions form a pair of handle or shaft portions 1a,
and the intermediate portion forms the structrual part 1b of
a head frame 2. A throat piece 3 is secured between the
handle portions 1a where they blend into the structural frame :
part 1b. ~
7 ~- :
'
., - .
, ' .
., ~, . .. . . . . . .. . ...
~5~
As will be apparen-t from ~igure 2, the met~l strip,
or at least the part 1b thereof~ is of generally "figure-of-
eight" or "dumb-bell" cross-section, and is formed in its
peripherally ou-twardly directed surface with a peripherally
extending undercut or dovetail recess 1co Overlying the
outer periphe~y of the structural frame part 1b is a
separate frame~reinforcing member in the form of a flexible
strip 4, a portion of which is shown in Figure 4~ ~he strip
4 is molded, extruded or otherwise formed from a substantially
incompressible and relatively hard syn-thetic plastics material,
such as toughened ~ylon or acetyl butadiene styrene ~referred
to hereinafter as ~B~) or other tough plastic or other
material. r~he thickness of the strip 4 in a direction
normal to the planes of the stringing 5, i.e. the spacing
between the opposite side surfaces 4a thereof, approximates
the thickness, in~the same direction, of the structural frame
part 1b,i.e. the~spacing between the opposite side surfac~s
1d thereof. The radial height of the side surfaces 4a,i.e.
in the planes of the stringin~ or direc-tions parallel thereto,
approximat~s that of the side surfaces 1dj and the height
of each side surface may, in one specific and non-limiting
e~ample of tennis racket, be ~" inchO The inner peripheral
surface of the strip 4 has a profile corresponding to tha-t of
the outwardly directed surface of the frame part 1h~ and
includes a longitudinally extending dovetail projection 4b
which interlocks with the recess 1c to retain the strip 4
positively anchored to the frame part 1b. 1`he pro~ection may
optionally be provided with one or more lon~itudinal channels
4c which impart resilience to the undercut slde surfaces of
the projection of the otherwise non-resilient strip, as well a
reducing the weight of the head and saving material.
. .
Stringing-receiving apertures 6 are bored or moulded
into the strip 4, between and opening into the side surfaces
4a thereof. In this embodiment, the longitudianl axes of
the apertures 6 are generally parallel to each other and
perpendicular to -the planes of the s-tringing 5. The cross-
section, for example diameter-, of the apertures 6 are gen-
erally parallel to each other and perpendicular to the
planes of the stringing 5. The cross-section, for example
diameter, of the apertures 6 is greater than -that of the
single or compound f`ilament, i.e. natural gut or synthetic
fibre, of which the tensioned s-tringing 5 is composed, so as
to allow the stringing filament to pass therethrough the
requisite number of times, l.e., once, twice or three times
depending upon the position of the apertures. The apertures
6 are bevelled, at least at their outer ends, and at least
where they engage the stringing 5, as indicated at 6a, so as
to increase, as much as possible, the radius of curvature of
the stringing during its transition from the apertures 6 to
the slde surfaces 4a, and to blend smoothly with the side
surfaces 4a, thereby to minimise chafing of, and localised
stresses in, the stringing. The apertures may additionally
be curved, bowed or angled downwardly towards their outer
ends as viewed in Figure 2 to reduce the sharpness of the
said transition.
The ends of the strip 4 blend into the frame part lb
adjacent the handle portions la, and, with regard to Figures
1 and 3, the throat piece 3 is provided with an inner margi-
nal portion 3a which is of the same -thickness as -the frame
portion lb and strip 4 so as to blend in with, and lie in
the same planes as, the side surfaces ld and 4a. The margi-
nal portion 3a is also provided with stringing-receiving
apertures 6.
`~
_ g _
.. . . .. .. . . . .
The portion 3b of the throat piece ex-tending away
from the head may be of any desired thickness or configur-
ation, and may be thinner than the portion 3a, as shown,
to save weight.
- 9a -
' ' " :':. - , , '
s~ o~
The throat piece may be molded or otherwise formed from metal or
a toughened synthetic plastics material of sufficient strength
to resist the tensional stresses of double stringing, and may,
for example, be formed from any of the materials from which the
strip 4 may be made, or from a reinforced plastics material.
The stringing filament is passed through the apertures 6 in
the frame part la, and throat piece 3 back and forth across the
opening surrounded by the frame, 50 as to produce two intercon-
nected sets of appropriately tensioned string portions, one set
5a, 5b lying in the plane which is generally flush with the plane
of the side suxfaces ld and 4a of the frame part and strip which
are uppermost in Figure 1, and the other set 5c, 5d lying in a
plane parallel to the plane of the first set 5a, 5b and generally
flush with the plane of the opposite side surfaces of the frame
part and strip which are lowermost and concealed in Figure 1.
Each set comprises two groups of substantially parallel string
portions, the string portions of one group 5a or 5c being
generally perpendicular to, and interwoven with, the string
portions 5_ or 5d respectively of the other group. The dis- -
tribution or mutual spacing of the apertures 6 around the frame
2 are such that the mutual spacing of the string portions in
both groups in each set is the same as, or similar to, those of
the string portions of a conventional centrally strung racket,
although this is not essential. However, in this embodiment
unlike conventional stringing, the string portions in both groups
extend diagonally, i.e. at approximately 45, to the lonyitudinal
axis o~ the racket handle, although the string portions could
alterna-tively be disposed generally perpendicular and generally
parallel to the longitudinal axis, as in conventional s-tringing.
In any event, additional string portions may be provided,
such as those indicated at 5e,
. ~
.
58~
disposed adjaaen-t to, and overlying, the frame 2, which
portions would not be present in a conventional, centrally
strung racket, irrespective of the orientation of the string
portions.
Although -the ends of the stringing may be anchored by
knots which cooperate with the ou-ter ends of one or more
of the apertures 6, since these knots may project from
the planes of the side surfaces they could be engaged by,
and adversely deflect, a ball striking the frame. For
this reason one or more of the apertures may be of stepped
cross-section so as -to recieve and anchor the knots totally
within the apertures. A~ternatively, the stringing may
commence and terminate in knots located at the peripherally
outer ends of additional and generally radially extending -
aperttlres(nt shown), i-e., apertures extending between and
,1 opening through the peripherally inner surface of the
frame part and the peripherally outer surface of the over-
lying strip, or between the peripherally inner surface of
the throat piece 3 and the peripherally outer surface or a
side surface thereof.
Due to the length of the stringing filament required,
the stringing is preferably produced ~rom two or more
separate lengths of filament. ~or example, one length may
be employed to produce the string portions 5_ and 5c, whilst
, another length may be employed to produce the portions 5b
', and 5d. although this is not essential, and the racket could
be strung with a single continuous filament.
In the embodiment of ~igure 1, the longitudinal axes
of the apertures 6 are mutually parallel, and perpendicular
to the parallel planes of the sets of string portions, so
t tha-t the string portions 5a and 5b of one set diverge
-- 11 --
,
relative to the string portions 5c and 6_ respectively
of -the other se-t when viewed in plan. Alternatively, the
axes of the apertures could be inclined relative to said
planes, so that the string portions of one set are parallel
to and aligned with, or alternatively parallel to and offset
with respect to, the string portions of -the second se-t, as
viewed in plan.
The side surface ld and 4a of the frame part lb and
s-trip 4 are substantially flat and coextensive, so that
stringing 5 will lie on the side surfaces, although the
side surfaces could be recessed to accommodate the stringing
if required, or raised locally in the vicinity of the
apertures, so that the stringing will be spaced, for example -
by approxirnately l/8 inch, from the side surfaces. The ap-
ertures 6 are preferably located as near to the outer peri-
pheral surface of the strip 4 as possib~Le, for example
approximately l/8" or less from the latter surface. Since
the frame 2 carries tensioned stringing on both sides there-
o-E, it is subject to approximately twice the loading which
is imparted to a conventional, centrally strung racket head
due to the tension in i-ts string portions, and the structu-
ral frame part lb will be dimensioned, or strengthened, to
resist this additional loading.
The racket shown in Figures l to 3 may be simply formed
by bending a length of the extruded aluminium s-trip to the
required shape of the handle portions la and frame part lb.
and then assembling the extruded strip 4 thereto by intro-
ducing the dovetail project:ion 4b longitudinally into the
recess lc and sliding the strip 4 around the periphery of
the frame part lb until it is positioned as
_ 12 -
; ~ , ' '. "
, ' :: :: . . .
8~
shown. This position is preferably accurately prede-termined
by cooperating means, such as shoulders or steps (not showr~).
The dovetail projection 4b may be introduced into the
recess lc at the free end of one handle portion la, or may
be introduced adjacent one side of the handle where the frame
part lb mee-ts the handle, which may require modification of
the undercut side walls of the recess lc a-t the zone of
insertion. Alternatively, the projection 4_ may be snapped
into the recess lc due to the resilience imparted to the ~ -
undercut side surfaces of the projection 4b by the channel
4c. The throat peice 3 is permanently secured in place, for
example by screws, rivets,; an adhesive, or combinations
thereof, or by any other suitable securing means. The strip
4 may be secured in place in a similar way, although this
is not essential. The stringing-receiving apertures 6 may
be bored in the strip 4 and throat piece 3 after assembly to
the frame, although preferably these apertures are formed,
for example, moulded in or bored, prior to assembly,
The stringing 5, tensioned for example to 55 to 60
pounds or more, is then strung as previously described.
The metal strip, or at least the s-tructural frame part
lb thereof, and the flexible overlying strip 4, may -take a
variety of different forms. For example, the frame part l_
may be of generally H cross-section as shown in Figure 5,
instead of "dumb-bell" section as shown in Figure 2, and the
frame part lb and strip 4 may be provided with a parallel-
sided interfitting recess lc and projection 4b, In this
case, the frame part lb and strip 4 may be secured together
by securing means as previously described, or may be simply
retained assembled together by virtue of the tensioning in
the stringing 5.
- 13 -
~s~
By employing a flexible strip of the type described
existing conventional, cen-trally strung rackets may be
converted to double stringing, and this may be achieved
without any modification of the existing conventional
frame. The conversion is of particular application to
metal framed rackets, for example, those designed by the
Maark Corporation of Cranbury, New Jersey, U.S.A., and
Figure 6 shows this conversion as applied to a "dumb-bell"
section frame as disclosed in their British Patent No:
1,311,925. The conversion is achieved by removing the con-
ventional central stringing, and attaching a flexible strip
7~similar to the strip 4, to the outer peripheral surface
of the metal structural frame part 8. This flexible strip
is manufactured as an accessory or separate entity, and is
profiled as shown so as to fit the contours of the existing
frame part 8. In particular, the strip 7 is provided with
a continuous rib 7a which locates in a corresponding channel
8a in the outer peripheral surface of the frame part, the
rib 7a being optionally formed with bosses 7b which engage
in some or all of the conventional stringing-receiving aper-
tures 8b in the central web of the frame part. The bosses
7b serve to locate the strip 7 relative to the framé part,
and the strlp may additionally be held in place by any of
the securing means previously described, or merely by the
stringing 5. The strip 7 is pro~ided with stringing-re-
ceiving apertures 9 and double stringing as previously
described.
The existing throat piece of the centrally strung rac-
ket will, in all probability, no-t be suitable for double
stringing. In this event, the packaged accessory or
- 14 -
conversio~ ~it as marketed will include not only the required
length of s-trip 7 or e~uivalent1 but also a suitable double
stringing thloat piece such as the throat piece 3 shown in
Figure 7, which may, for example9 be similar to the throat
piece ~ previously described, to replace the exis-ting throat
piece of the convent~nal racketO Alternatively, an appropriate
adaptor may be provided for the existing throat piece.
~he existing frame or structural part of conventional,
centrally strung rackets as just described may possess the
drawback that it lS of insufficient streng~h to withstand
double stringing. However, this drawback is eliminated or
alleviated since the overlying strip 7 or equivalent, since it
.
is made from a relatively hard and incompressible materia},
significantly reinforces or form a structural p~rt of, the
frame. ~his reinforcing effect could be enhanced by forming the
overlying strip from, or reinforcin~ it with, a reinforcing
matsrial~ such as graphite or carbon fibre, or associating it
with a metal strip~ wire or wires which may be embedded in the
overlying strip, and positively securin~ the overlyinG strip
to t;he frame, so that the strip becomes a lamination forming
an integral part of the frame. ;
- ~
- 15 - ~
... ... . .. ..
,:
Double-strun~ rac1cets embo~ying this invention, possess
numerous advantagesO
In conventional, centrally strung rackets in whtch the
stringing-receiving apertures are bored, after formation of
the frame, between the inner and outer peripheral surfaces
of the frame, these aperturesp which are up to ~0 in numb~r,
have to be bored from up to 80 different directions. In
addition, the outer peripheral surface of the frame, at least
in some regions thereof 9 must be routed or grooved between
apertures, to receive the stringing and protect it from damage,
for example when the frame is s-truck against the ground.
~or these reasons, hand-made conventional frames are
difficult and expensive to produce, as are mass-produced
frames due to the complexity and cost of the mass production
machines required to simultaneously bore aper-tures from up to
80 different directions and to effect the routing. Furthermore
even if the frame is of molded construction,the conventionally
placed apertures would similarly render it relatively complex
~and costly, from a pxactical point of view, to mould the frame
in one piece~
With the double strung racket embod~ing the invention~
however, the metal strip forming the structural frame part 1b
and handle portions 1a may be mass produced, i.e. extruded
or moulded, in straight lengths to the required profile, and
~ simply C1lt to len~th and bent to the reguired outline. ~he
costly process of drillin~ or boring stringing-receivin~
aperture~ in the frame part is therefore totally eliminated,
the strength Or the frame part is not impaired hy the
provision ol ~ly strin~in~ receiving apertures, and the
design or configuration o~ the frame part is not limited by,
or dependent upon the need to provide, such apertures,
16
: .
.......
The plastics overlying strip 4 may likewise be mass produced
by extrusion or moulding to the required profile, and the
stringing-receiving aper-tures may be formed during this
production, or s~lbseguen-tly, ei-ther before or af`ter assembly
of the s-trip 4 to t;he frame part 1b~ When the apertures are
preformed, appropriate steps will be taken to ensure that
they will be correctly and accurately positioned around the
frame pa~t after assembly of the strip 4. The throat piece
3 may likewise be mass produced by mouldin~ or any other
appropriate process, with or without the stringing-receiving
apertures pre-formed therein.
The overlying strip 49 irrespective of whether it is
secured in place permanently, e.g. by an adhesive, temporarily,
e.g. by reIeasable fRsteners1 or merely held in place by the
strin~in~, may be readily replaced when restringing~due to wear
or changes in design, whilst retaining the same basic
~structural frame part 1b.
Due to the smoo-th, round-edged outer peripheral surface
of the frame which is preserved by the strip, the airflow
around the frame during play is improved, and drag is
reduced.
In the illustrated embo~iments~ the stringing is
cushioned or isolated from the struct;llral part of the frame,
particularly where the strin~ing-receiving apertures open
into the side surfaces of the frame and the radius of
curvature of the stringing is relatively tight, by the
overlying strlp 4 formed of a plastics or other material
which,although it is substantially incompressible and -~
relatively hard so that it will form a composite laminated
structure wi-th, and therefore significantly reinforce, the
~0 frame, is more compatible with the stringing than the
- 17 -
,
s~
materi.al of ~le structural frame part 1b. '~his tends to reduce
chafing or other wear of the stringing, and reduces or
distributes localiæed stresses. This is of particular
significance when, as illustrated, the frame is made of metal,
which is less compatible with the stringing than is wood.
Since the stringing passes through apertures extending
between the opposite side surfaces, not the peripheral surfaces,
the risk of damage if the frame strikes the ground, is avoided
without the expense of routing necessary in conventional
rackets.
In ball games played within the confines of a walled
court 9 such as Sguash, in which the racket frame of-ten strikes
the walls, the use of a racket employing a metal frame which
is exposed at its outer periphery is often forbidden, due to
the substantial risk of damage, for example, chipping, of the
court walls, duè to the racket frame striking the walls
~his risk is eliminated or substant:ially reduced by the
provision of the overlylng strip 4, as is the risk of injury :
to a player when struck by a racket:. In addition, the strip 4
cushions the metal frame part~ and eliminates wear thereof,
when the frame strikes the walls or floor of the court, and
any resultant éxcessive wear or damage of the strip 4 merely
nece~sitates the replacement of the strip, not of the-whole
racket O
It will be understood that various modifications may be
made without departing from the scope of the present inventlon
as defined in the appended claims.
- 18 ~
.
,
.,
8~
For example, the axes of the stringing-receiving
apertures may be inclined relative to the planes of the
playing surfaces, to produce two sets of string portions
which are mutually parallel, instead of divergent as shown,
whilst employing -the stringing technique as herein
described and shown. The string portions may, in this case,
be either precisely aligned when the frame as viewed in
plan, i.e. in a direction perpendicular to the planes of the
~ets of string portions, or staggered so that the string
portion of one set lie half way between the string portions
of the o-ther set.
Alternatively, the aforementioned parallel stringing
may be achieved without inclining the axes of the stringing
receiving apertures, by employing a different strlnging
technique. In this technique, the stringing filament is
passed through a first aperture, across a first side surface
of the frame, across the opening in the frame to the opposite
or second aperture, though this second aperture from said
first side surface to the second side surface, across the
opening to, and through, the first aperture, from the second
side surface to the firs-t surface, along the first side sur-
Eace to the next adjacent or third aperture, through -
the third aperture to the second side surface and across the
opening to the opposite or fourth aperture adjacent the
second aperture, through the fourth aperture and across the
opening to, and through, the third aperture to the second
side surface~ and along the second side surface to and
through the next adjacent fifth aperture. This procedure
is repeated to complete the strlnging. It will be apprecia-
ted that this
'
stringing -technique will require at least some of the
stringing-receiving apertures to be of enlarged cross-section
to accommodate the additional passes of the stringing.
The foregoing parallel stringing technique produces
the string portions of the two sets alternatively. However
the parallel stringing could be achieved by producing the
string portions of one set and then o-f the other set. I~
this technique, the stringing filament is passed through a
first aperture, across a first side surface, and the opening
in the frame, to and through a second opposi-te aperture -to
the second side surface, along the second side surface to
the next adjacent or third aperture, through the third aper-
ture to the first side surface and back across the opening
to the opposite or fourth aperture next to the first aper-
ture, through the fourth aperture to the second surface and
along that surface and through to the next adjacent fifth
aperture. This procedure is Gontinued to complete the string
portions of one set, and is then repeated to produce the
string portions of the other set.
In some games, it would in theory be advantageous to
be able to play some types of strokes or shots with string~
ing tensioned to a par-ticular value or range, and to play
other strokes with stringing tensioned to a higher or lower
value. This can be achieved by, and -the feature incorporated
in a double strung racket embodying this inven-tion, since,
for example by employing the stringing technique just des-
cribed, the string portions of one set can, during stringing
be readily tensioned to a higher or lower value than that
of the string portions of the other set.
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: .
~59~9S~
As has already been mentioned, frames of double strung
rackets must be able to withstand considerably higher
stresses than conventional rackets, since the forces -to
which the frames are subjected due to the tensioning in the
two sets of string portions are approximately doubled. For
this reason, apart from modifying the dimensions, cross-
sectional shape or other design features of -the frame, or
the structural part thereof, to withstand these increased
forces, when the frame is formed from a material or materials
possessing increased strength may be employed. For example,
conventionally employed, i-t is envisaged that o-ther materials
the frames may be formed in whole or ln part from, or may
be reinforced or combined with, materials such as carbon or
graphite fibres, or molybdenum fibres, or the like, or
glass fibres in varying proportions to provide the required
rigidity, always bearing in mind theStrength/cost ratio.
The overlying strip shown in the drawings!~may extend
along the recess in the handle portions in addition to the
frame part, and in this event the strip may extend to the
free ends of the handle portions, or may terminate adjacent
or under the hand grip carried by -the handle portions. The
strip, where it extends along the handle portions, may be
reduced in height by removing all or part of the aperture-
containing part thereof, so that the strip will provide a
substantially smooth contour to, and blend in with, the
peripherally outer surfaces of the handle or shaf-t portions.
Although the overlying strip 4 shown in the drawings
preferably extends continuously around the frame from oppo-
site sides of the handle, the single strip 4 may be replaced
by two or more, for example in a plurality of, spaced strip
or insert portions, each provided with one or more s-tringing-
receiving
- 21 -
.
5~
apertures, bosses, or other stringing anchoring or
accommodating means. The strip or strip portions may have
the same side surface-to-side surface thickne~ a~ th~
frame, or may be thicker or thinner.
Instead of providing the illustrated me-tal-framed
rackets with a separate overlying strip, the strip could be
built up on, or bonded to, the frame part 1b.
The frame part and/or the handle portion may be made
from, or include, metal, for example cast aluminium or.
other light-metal or alloy, laminated wood, synthetic
plastics material~ carbon fibre, glass fibre, or any
other suitable material, or comblnations thereof.
Although the stringing is preferably located in
stringing-receiving aper-tures which extend between and ope~ -
through the opposite side surfaces of the overlying strip 4 :.
or equivalent? the apertures could be replaced by grooves
in the outer peripheral surface and/or one or both side
surfaces o~ -the strip 4, in which the s-tringing is located
and laid. When the frame possesses sufficien-t strength,
the strip or ~trips may be omitted, and the stringin@,-
: receiving grooves would then be formed directly in -the
outer peripheral and/or one or both side surfaces of the
frame~
~When the frame possesses sufficient strength, the :
stringing-receiving apertures,preferably bevelled or other- ~. ~
25 wise blended or shaped at their outer ends, may be formed .~ .:
in the frame or structural frame part thereof, instead
of in a peripherally overlying strip as specifically
described and illustrated~ For example, when khe .. -~
structural frame part is of tubular.form, made, for
30 example from metal~ or a "pultruded" reinforced plastics
material as described hereinafter, the apertures may be
_22 _
" , ,, . , ; , , ;. , : . .: :: , , " ; , .,
,: ~ . , , ,. :" ,. ,
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~315a~
located generally centrally between the inner and outer
peripheral suraces of the tubingl for example diametrically
in the case of circular-cross section steel or other metal
tubing.
~he apertures, when formed directly in the frame as just
described, may be lined with linings or sleeves of ma-terial
more compatible wi-th the stringing than the metal or other
material of the frame. In onesuch embodiment, press-fitted or
bonded into each aperture from opposite ends thereofj are
two separate insert members or grommets formed from a
relatively hard and incompressible plastics material, such as
toughened Nylon or ABS, or from a resilient material such as
a natural or synthetic rubber or any other suitable material.
Each insert member comprises a tubular body terminating in
an annular washer-like head at its outer end which surrounds
the aperture in the frame and abuts the adjacent side surface
of the frame~ These insert members serve to protect thè
stringing from chafing against the relatively hard material
of the frame, and the washer-like heads thereof serve to
space the s-tringing away~from the side surfaces, for example
by ~ inch. If required, the washer-like heads could be
omitted, and a single Iength of sleeving could extend through
each aperture and partly overly the opposite side surfaces
of the frame.
The assembly of the individual grommets or inserts to
the individual apertures in the frame may be a tedious and
I;ime consurning operation. This may be ~lleviated, and the
frame may be simultaneously significantly reinforced,
by moulding the inserts, or groups of the inserts, integrally
with an interconnectin~ web, the web being joined to, or
- . , ~ ,
f~ S8~.
replacing, the washer-like heads of the inserts.
Alternatively, the washer-like heads may s-tand proud of the
web to form washer-like heads serving to space the
stringin~ from the web. The mutual spacin~ of the inserts
will correspond to the mu-tual spacing of the apertures, and
the web will be curved, or capable of being flexed, to
correspond to the curvature of the frame as viewed plan~ i.e.
as shown9 in effect, in Figure 1, and may define a closed or
continuous loop. Thus, by superimposing such a web on each
side surface of the frame, the bodies of the integral
inserts will he approximately aligned with their associated
apertures, and may be readily pressed into their apertures,
either ~uccessively or simultaneously, until the web, which
may be coextensive with the side surface, lies on the latter.
When sald inserts are provided,irrespective of whether
they are separate, or joined by a web~ the apertures in the
frame need not be bevelled or otherwise finished, the
bevelling and finish being provided in the inserts.
The webs with their integral inserts, or eguivalent
apertured strips which may simply replace -the latter, may be
made from a frame-reinforcing material other than these
hereinbefore referred to, such as glass fihre or a reinforced
plastics material, and may be bonded to opposite side
surfaces of the frame so as to enhance reinforcement of the
latter. Such webs or strips could also be bonded to
conventional frames, for example~ wood frames to convert
the frames to double stringing whilst reinforcing said frames
to resist the increa~ed loading.
Such webs or strips, which may take -the form of a pair
of closed loops, may each be extended so as to be of
_ 21~ _
.
.; '
51~3~
generally L-shaped cross section, so tha-t the base of the L
overlies a side surface of the frame, and the side limb of
the L overlies up to one half of the width of the outer
peripheral surfaces~ Alternatively, the webs or strips could
each be of ~enerally U-shape instead of L-shape, the side
limbs overlying up to one half of the width of the inner and
outer peripheral surfaces of the frame.
Thus, in bo-th cases, the webs or loops form half
shells which are bonded -to, and clad, ~he frame, further
increasing the strength of the frame.
When the apertures are formed direc-tly in the frame
- and the frame is ~rmed from laminated material, for example
from wood and/or glass fibre and/or plastlcs and/or metal,
the pla~es of the laminations may extend generally
perpendicular to the planes o~ the stringing 6, as in
conventional laminated racket frarnes. In this event, the
apertures should preferably be bored ou-twardly of, but
adjacent a relatlvely hard lamlnation, such as a glass fibre
lamination. However, the frame may alternatively and
advan-tageously be laminated flat, i.e. the planes of some
or all of the laminat~ns may extend generally parallel to the
planes of the stringin~. This form of lamination should be
superior to conventional lamination9 since the apertures
extend generally perpendicular to the planes of the
laminations, and the tension in the stringin~ acts in
directions general]y parallel to the planes o~, and the -
major dimensions ol`, the laminations~
When the ape~tures are formed directly in the frame
as prev~usly described, since the apertures extend parallel
or ~ubstantially parallel to each other between opposite
side surfaces of the frame, the formation o~ the apertures,
_25 -
which may be effected by boring, drilling, pressing, stamping,
punching or moulding, is a relatively ~imple, rapid and cheap
operation, whether carried out manually or automatically.
When carried out auto~atically, the apertures may be formed by
means of a multi-head or multi-spindle machine, instead of the
far more complex machinery employed in conventional racket
automated manufacture.
When the frame is moulded, it may be moulded in one piece,
and the apertures may be formed at the same time, or subsequently.
It will be appreciated that the foregoing are only some
of the many alternative stringing techniques or configurations
which may be employed. The stringing-receiving apertures~grooves
or equiv~ent stringing-accommodating means, may likewise take
a variety of forms and cross-sections, and be disposed in various
positions and extend in various directions.
As an alternative to providing the peripherally overlying
strip with stringing-receivlng apertures as described with~
reference to -the drawings, the strip coul~ be provided with
integral or assembled bosses or eguivalent around which the
stringing is looped, located and anchored. The webs or strips
provlded on the side surfaces of the ~rame in the previously
described alternative but non-illustrated embodiment, could
also ~e provided with such bosses, or with stringin~-receiving
grooves, or e~uivalent.
-26
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The frame or frame part could be made from materials
and by techniques other than those herein described. For
example the frame or frame part could be made from a -tube
or tubes formed -from glass fibre rein-forced thermo-se-tting
resins, possibly reinforced with continuous and/or over-
lapping chopped carbon -fibres, by ex-trusion, or by a
"pultrusion" technique in which, as opposed -to ex-trusion,
the tube, or integral group of two or more tubes, is pulled
from the forming die. The tubing is formed to the required
frame outline whilst still hot and formable from the die,
whereafter it sets to its final outline. For example three
tubes may be simultaneously and integrally formed, the tube
configuration being such that as viewed in cross section,
the centre of the central tube is coincident wi-th the base
or intersection of the side limbs of an imaginary V, and the
centres of the other tubes are coincident one with each of
~the side ~imbs. With this configuration, the tubes will
., . ~ .
define an undercut channel which would serve to receive an
undercut projection on an overlying strip, in a manner
analogous to that described with reference to Figures 1 to 4.
~ lternatively, the frame, when formed from laminations,
could include one or more in-termediate layers of an expanded
rigid foam, such as expanded polystyrene, polyurethane or
other foam or "honeycomb" material, bounded by relatively
hard laminations, for example of a carbon fibre-reinforced
resin. By varying the densi-ty of the foam, the weight of
the racket head ma~ be predetermined.
The expanded foam or honeycomb could be preformed to
the outline of -the racket head and handle or shaft -to form
a core therefore, and could be bonded to and clad wi-th two
- 27 -
generally U-section half shells~ each in the form of a
continuous loop and integral handle portion formed from
the aforementioned relatively hard lamination material, and
each shell forming one side surface and half the thickness
or widl;h of the inner and outer peripheral surfaces of the
frame and handle. The shells may be apertured before or
after bonding to the core to form -the stringing-receiving
apertures~ may be provided with inwardly direc-ted tubular
bosses, and/or washer-like heads, or may he provided with
bosses around which the stringing is anchored, similar to
those just describedO
The foregoing honeycomb,laminated or sandwich
constructions are strong, particularly in torsion and bend.
The frame, frame part~ inserts, overlying strip or ~ -
web, and/or throat piece, or at least the stringing-engaging
regions thereof, may be formed from carbon fibre-reinforced
nylon, since the presence of the carbon fibre in this
composite can significantly reduce the coefficient of frlction
of the composi-te~ and thus reduce the wear of the stringing
due to chafing on the composite. Stringing i~ also
facil~ated, since the string portions may more easily
slide through the apertures during threadine and tensioning.
,.'",
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- 28 -
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