Tension tester for tennis racket strings

A device for determining the string tension in the netting of a racket has a base and clamping structure adapted to be intercoupled on opposite faces of the netting, and a compressible, spring-loaded plunger slidably mounted on the base for shifting movement against one face of the netting. Movement of the plunger against the face of the netting deflects the latter and also compresses the plunger such that an equilibrium position is reached wherein the compression force on the plunger spring is equal to the resistance force presented by tension in the strings of the racket netting. A tension gauge is provided for measuring the deflection of the netting at the equilibrium point and translating the deflection measurement into a tension reading corresponding substantially to the actual tension in the racket strings.

This invention relates to tension measuring devices in general and 
particularly concerns a tension tester adapted for measuring the tension 
in tennis racket strings and the like. 
The recent substantial increase in the popularity of tennis and other 
racket-type games has resulted in an accompanying boom in the industries 
supplying and servicing rackets. Particularly, a notable increase in 
demand has been experienced in racket restringing, probably for the reason 
that rackets today are very expensive and they are used more actively than 
ever before. Thus, rather than simply purchasing a new racket when the 
strings become worn, more and more players are having their rackets 
restrung to salvage an otherwise useless racket. 
One problem experienced in the racket restringing art relates to 
duplicating the original string tension so that the racket owner does not 
experience a significant change in the playing characteristics of his 
racket after it has been restrung. This problem is particularly 
significant since few racket owners know the string tension of their 
rackets even though this tension value is extremely critical in providing 
a player with a racket suited to his ability and style of play. Moreover, 
there has heretofore been no device available for determining the tension 
in the strings of a racket after it leaves the stringing machine. Hence, 
the racket stringer has no way of precisely duplicating the original 
string tension when it is time to restring the racket. 
Accordingly, it is an important object of the present invention to provide 
a device for determining the tension in tennis racket strings even after 
the racket has been removed from the stringing machine. 
It is yet another important object of the present invention to provide a 
racket string tension tester wherein no part of the tester comes into 
contact with the racket frame. 
It is another important object of the instant invention to provide a 
tension tester for tennis racket strings wherein a spring-loaded plunger 
is pushed against one face presented by the racket strings for deflecting 
the strings in relation to the amount of tension therein. 
It is a further important object of my invention to provide a tension 
tester for tennis racket strings wherein portions of the device are 
disposed on opposite sides of the netting defined by the racket strings 
and structure projects through the netting for intercoupling the opposed 
portions of the device.

In FIG. 1 there is shown a tension-testing device 10 including a base 12, 
clamping structure 14 releasably coupled with the base 12, and a 
spring-loaded plunger 16 slidably supported on base 12 for movement toward 
and away from clamping structure 14. As shown for example in FIG. 4, the 
device 10 is intended to be emplaced on the netting 18 defined by strings 
20 of a tennis racket 22 in such a manner that the base 12 is positioned 
against one face 24 of the netting 18, while the structure 14 is 
positioned against the other face 26 of the netting 18. 
The base 12 presents a generally T-shaped configuration having an elongate, 
hollow handle 28 depending from a rigid crosspiece 30. The crosspiece 30 
has an elongate, substantially flat edge 32 facing away from handle 28 and 
adapted for emplacement against the face 24 of racket 22. A pair of legs 
34 are positioned on opposite ends of the crosspiece 30 and extend 
upwardly beyond the edge 32, each leg 34 having a transversely extending 
notch 36 for a purpose to be described hereinbelow. 
The base 12 further includes an elongate, hollow barrel 38 positioned at 
the juncture between crosspiece 30 and handle 28 and in axial alignment 
with the latter. The barrel 38 has an open end 40 positioned adjacent edge 
32 and an opposed open end 42 in communication with the hollow handle 28. 
The plunger 16 is supported within barrel 38 for rectilinear movement along 
a path of travel extending parallel to axes of the handle 28 and barrel 
38. Plunger 16 includes a cylindrical face-engaging section 44 adapted for 
movement in and out of open end 40 and having a generally circular, 
outermost contact surface 46. The end of plunger 16 remote from section 44 
has a substantially cylindrical slide section 48 axially aligned with the 
section 44. A resilient section in the form of a coil spring 50 extends 
between the sections 44 and 48 such that the plunger 16 is itself 
compressible when resistance to movement is encountered at surface 46. 
Spring 50 is retained in axial alignment with the sections 44 and 48 by 
virtue of its engagement with a cylindrical boss 52 on section 48 and a 
cylindrical recess 54 in section 44. 
Movement of plunger 16 relative to base 12 is effected by mechanism 
defining a toggle linkage 56 pivotally secured at one end to base 12 by a 
pin 58 and similarly supported at its opposite end to plunger 16 by a pin 
60. The linkage 56 includes a pair of rigid links 62 and 64, the latter of 
which presents a grip 66 to facilitate forcible actuation of the linkage 
56. 
It is to be understood that operation of toggle linkage 56 serves to move 
the plunger 16 along its rectilinear path of travel. Thus for example, as 
shown in FIG. 2, when the linkage 56 is in its retracted position, plunger 
16 is carried entirely within the barrel 38 having no portion extending 
beyond the open end 40. On the other hand, as shown in FIG. 3, when the 
linkage 56 is moved to its extended position, the plunger 16 is caused to 
move relative to barrel 38 and base 12 such that the face-engaging section 
44 passes through end 40 and beyond edge 32. It will be appreciated that 
when the linkage 56 is fully extended, the slide section 48 of plunger 16 
is disposed at a fixed position within the barrel 38, and accordingly, the 
face-engaging section 44 likewise is disposed at a fixed position. Note 
however, that should resistance be encountered at surface 46, the plunger 
16 will compress such that while slide section 48 remains in its fixed 
position, the position of face-engaging section 44 is dependent upon the 
force encountered by surface 46. It is this feature of the device 10 that 
enables it to measure the tension in strings 20. 
The clamping structure 14 essentially comprises a flat plate 68 having a 
pair of spaced, coplanar, face-engaging pads 70 and 72 adapted to be 
positioned in contact with the face 26 of netting 18. A pair of threaded 
pins 74 project outwardly from plate 68 immediately adjacent respective 
pads 70 and 72. The pins 74 are arranged to engage the notches 36 of legs 
34 when the device 10 is positioned on racket 22 with the legs 34 of base 
14 projecting through the netting 18. With this arrangement there is 
presented coupling means whereby the structure 14 may be selectively 
coupled with the base 12 to preclude relative movement between the latter 
when operating the device 10. The coupling means further includes a pair 
of threaded caps 76 cooperably engageable with threaded pins 74 for 
maintaining the selective coupling between the structure 14 and base 12. 
The plate 68 carries a tension gauge 78 having a rack 80 supported over 
surface 46 for rectilinear movement in a direction parallel to the 
movement of plunger 16, and a corresponding pinion 82 in mesh with rack 80 
and supporting a needle 84 for movement through an arcuate path of travel. 
Gauge 78 includes a dial on plate 68 comprising a plurality of spaced, 
raised numerals 86 sequentially arranged in an arc and representing 
graduated tension values. It will be appreciated that rectilinear movement 
of the rack 80 effects rotation of the pinion 82 and hence swinging 
movement of the needle 84 along the dial presented on plate 68. As shown 
in FIG. 1, there is provided a stop 88 which prevents the rack 80 from 
separating the structure 14, and additionally, rack 80 has a lowermost 
foot 90 adapted to be positioned directly over surface 46 when the device 
10 is properly emplaced on the racket 22. 
At this point, the relationship between the spring 50 and the gauge 78 
should be further described in order to clearly explain the invention. 
From the foregoing description it will be appreciated that when plunger 16 
is pushed to its outermost fixed position by the extension of linkage 56, 
the netting 18 will be deflected. In addition, plunger 16 will be 
partially compressed due to compression of spring 50 in response to 
resistance against deflection of netting 18. Manifestly, netting 18 will 
resist deflection in direct relationship to the amount of tension in 
strings 20 such that the compression of spring 50 is inversely related to 
the tension in strings 20. Accordingly then, gauge 78 and spring 50 are 
coordinated such that the tension reading given by gauge 78 for a certain 
deflection of netting 18 (and corresponding compression of spring 50) 
coincides with the actual tension in the strings 20. 
In use, the operator first positions the device 10 on a racket 22 in a 
manner shown in FIG. 4. This is accomplished by initially separating 
structure 14 from base 12, positioning base 12 against face 24 such that 
legs 34 project upwardly through netting 18, and then emplacing structure 
14 against face 26 in such a manner that pins 74 are captured within 
respective notches 36. In order to secure the device 10 in its 
tension-testing position, the operator preferably screws the threaded caps 
76 onto their respective pins 74. 
Once the device 10 has been properly emplaced, the operator merely 
depresses grip 66 to extend linkage 56 and hence push plunger 16 against 
face 24 of the netting 18. Such movement will cause deflection of the 
netting 18 as well as compression of the plunger 16 in a manner similar to 
that described and shown, for example, in FIG. 6. 
The deflection of netting 18 will be sensed by tension gauge 78 through 
movement of rack 80 thereby causing indicator needle 84 to move to a 
position along its arcuate path of travel. The operator simply views the 
position of needle 84 to determine the tension in the strings 20 of 
netting 18. 
The present invention offers a relatively inexpensive means for testing the 
string tension in rackets prior to restringing of the latter. This highly 
desirable function is accomplished without engaging the racket frame in 
any way and consequently, there is virtually no possibility of damaging 
the racket itself. 
The tension tester of the present invention can be used at any time such 
that racket string tension may be measured long after the racket is 
removed from the stringing machine. Additionally, since it is unnecessary 
to cut or otherwise destructively operate on the racket strings, the 
testing device of the present invention also can be used to check the 
string tension in new rackets if so desired.