Plastic Tennis Racket Having Predetermined Cross Sections Effecting Flexibility

Abstract

A tennis racket frame of molded plastic includes head, shaft and handle portions with the cross sections thereof, together with the characteristics of the plastic material, providing maximum flex at the upper end of the head, secondary flexing at the throat area adjacent the head, lesser flexing at the base of the head, and the minimum of flexing at the shaft adjacent to handle. Shaft apertures and texturing of the handle can be molded in at the same time that the proper cross-sectional areas of these parts are formed. The cross-sectional area of the head is T-shaped and the string apertures are bridged by guides about which the strings extend in order to reduce wear thereof.

Description

GENERAL

Tennis racket frames are normally made of wood or metal which can provide many of the necessary physical properties for satisfactory performance. However, during use there are generally problems of racket distortion with the passage of time, for example warping of a wooden racket, or distortion with actual use, for example bending of a metal frame. In providing a racket with proper playing characteristics of balance and "feel," as well as desirable durability, the cost of manufacture increases considerably.

SUMMARY

An object hereof is to reduce the cost of racket manufacture by forming the frame of a molded plastic.

Another object is to form a tennis racket frame which has minimum distortion over a period of time and which has minimum response to temperature and humidity changes.

Another object is to provide a plastic tennis racket which has the flexibility, strength, and weight to exhibit highly desirable playing "feel" and balance.

In a specific form the tennis racket hereof includes a frame which is preferably formed of a molded plastic such as polycarbonate resin with up to 20 percent glass content. The shaft and throat areas are apertured, and the cross section of the loop which forms the head is made generally T-shaped. These cross sections are related to the bending characteristics of the plastic such that the upper portion of the head has the greatest flexing characteristic, the throat area has the next greatest flexing characteristic, and the base of the head has a still lesser flexing characteristic. The shaft adjacent the handle has a still lesser flexing characteristic and of course the handle has the least flexing. In order to reduce string wear the T-shaped cross section of the head has string apertures which are bridged by raised portions or guides about which the strings pass through smoothed and rounded troughlike areas in order to increase the string life of the racket. The handle can have either a molded texture or can be separately wrapped depending on the grip desired.

THE DRAWINGS

In the drawing, FIG. 1 is a plan view of a tennis racket constructed in accordance with the invention;

FIG. 2 is a side view of the racket of FIG. 1 with the sections taken as shown in FIG. 1;

FIG. 3 is an end view of the racket of FIG. 1;

FIG. 4 is a greatly enlarged view of the string hole construction of the racket of FIG. 1;

FIG. 5 is a sectional view along the lines 5--5 of FIG. 4;

FIG. 6 is a modified form of the string hole construction of FIG. 4; and

FIG. 7 is a still further modified form of the string hole construction of FIG. 4.

DETAILED DESCRIPTION

The molded tennis racket of FIGS. 1-5 is preferably formed in one piece. The racket 10 includes (FIG. 2) a handle section A, a shaft section B, a throat section C, a lower head section D, and an upper head section E. The handle section A is hollow with an aperture 12 extending therein almost the full length of the handle. As shown in FIG. 1 the exterior of the handle is roughened or knurled at 14 providing a gripping surface.

The shaft section B, as well as the throat section C, include apertures 16 which help to provide the desired amount of flexing, discussed in detail subsequently, and also play a part in fixing the total weight of the racket which should be of the order of 12 or 13 ounces and similar to the weight of prior art wooden rackets. The apertures further help to establish the racket balance, that is the center of gravity.

The head of the racket 10 is in the shape of an oval as viewed from the plan view of the racket in FIG. 1 and has a periphery with a cross section in a generally T shape as visible in FIG. 2. The base of the T-shape 18 faces inwardly and the top of the T-shape 20 forms the outer periphery of the head. As seen in FIG. 1 the base of the T-shape 18 is apertured so that the strings can be passed through the apertures and strung across the racket in the usual woven pattern. Details of the stringing construction are discussed below.

The racket 10 is preferably molded in one step and composed of a plastic material which has the necessary mechanical properties. Consideration must be given to the impact strength of the material, since considerable force can be generated in the racket during use and to the fatigue characteristics of the material which may permit failure with age and use. Furthermore, there must be a proper degree of flexibility in order to have the proper feel and to avoid likelihood of breaking through brittleness. It should also be recognized that the head of the racket is under a considerable stress due to the tension of the strings 24 so that the material of the racket must have a minimum tendency to creep or distort under this stress with time. After repeated stressing and consequent racket deflection or bending through striking of the ball, the plastic material must have a memory quality such that it returns to its original undistorted shape. Plastic material will normally have virtually no moisture response, compared to wood, e.g., but it should be selected to avoid brittleness with low temperatures and distortion with heat normally encountered.

In addition to the above-described strength and aging properties it is, of course, also necessary that the material not be unduly dense so that the weight of the racket would go beyond that normally found in wooden rackets, which may be, for example, 123/4 ounces.

One suitable material for the composition of the racket is a polycarbonate resin which has been combined with approximately 10-20 percent glass fiber. One such plastic material is available, for example, under the trade name Lexan. Other suitable materials are acrylonitrile-styrene with 20 percent glass or acrylonitrile-butadiene-styrene with 20 percent glass.

We have also found that in constructing the racket 10 the various lettered portions thereof of FIG. 2 should have a certain relationship of flexing characteristics as the racket is viewed in FIG. 2, that is flexing in a direction transverse to the view of FIG. 1. This relationship is such that the upper head portion E has the greatest flexing characteristic, the throat portion C has the next greatest flexing characteristic, and the lower portion of the head D has a lesser flexing characteristic. The shaft B has a still lesser flexing characteristic, and the handle A has the least amount of flexing. These references to flexing characteristic all refer to bending of the racket as viewed in FIG. 2 with the handle section A clamped and the force applied to the outer end of the head. The relationship of comparative flexing is achieved by adjusting the cross sections of the various portions in relation to the bending characteristics of the material of the racket. For example, as seen in FIG. 2 there is a tapering of the head as it extends outwardly from the throat area C which promotes an increased bending characteristic in the upper head portion E. The throat portion C is tapered somewhat toward the shaft portion B as seen in FIG. 2 and further has the apertures 16 through the flat plan of the racket which can be adjusted in size to achieve the desired bending characteristic. Similarly, the apertures in the shaft section B can control the flexing characteristic of that portion to be less than that of the lower head portion D. It will also be recognized that the apertures 16 provide some advantage of reduced windage effect as the racket is swung in use.

Since the racket strings 24 are under a tension of 50 to 65 lbs., and since this tension increases considerably beyond that when a tennis ball is struck, wear can develop at the points where the strings contact the head of the racket. As shown in FIGS. 4 and 5 we contemplate the addition of raised rounded string guides or bunkers 28 to avoid having the string 24 pass around sharp corners.

The base of the T-shape 18 of the head has apertures 30 therein which are in pairs at opposite sides of the raised annular half-ring 28. As seen in FIG. 4 the strings extend from one side of the oval head to the other and pass under the T-shaped base or flange 18 and up through a hole 30. The string then passes around the circular periphery of the raised portion or guide 28 and down through the adjacent hole.

Modified forms of the string guide are shown in FIGS. 6 and 7. In the form of FIG. 6 the string 24 passes around the circular raised guide 28a which is molded integral with flange 18 of the racket head.

In the form shown of FIG. 7 the string 24 passes around a series of raised projections or posts 28b which are spaced in a circular pattern approximately corresponding to the periphery of the circular guide 28a of FIG. 6. It should be clear that other configurations beyond the half-ring guide 28 of FIG. 4, the circular guide 28a, and the series of posts 28b are possible to accomplish the smooth reversal of the string without creating focal points for strain.

The described tennis racket, formed of plastic, has the advantage of reduced influence by environmental conditions, for example as compared to the influence of humidity on a wooden racket. It also has the advantage of ruggedness and reduced cost, while at the same time maintaining a weight and playing "feel" much like other known rackets. The described flexing characteristics and the means of achieving them, as well as the means of anchoring the string in the racket head, contribute to an overall design which is both economical for manufacture in production quantities and highly durable and serviceable in use.

Claims

We claim:

1. A tennis racket frame for stringing including a closed loop head portion having a T-shaped cross section, with the base of the T projecting inwardly substantially parallel to the head plane and forming the string support structure, said racket frame further having a handle portion joined to said head portion at a throat portion by a shaft portion, all of said portions of said frame being an entirely one-piece molded plastic material reinforced with glass filler, each of said portions of said frame having a predetermined cross section, said shaft and throat portions having openings therethrough to coact with said predetermined cross sections to control and determine the flexing of said racket frame, and wherein the cross section of the upper portion of said head portion with respect to the cross section of said throat portion providing a greater degree of flexing transverse to the plane of said upper head portion than the degree of flexing of said throat portion, the cross section of said throat portion with respect to the cross section of said head portion adjacent said throat portion providing a greater degree of flexing of said throat portion than the degree of flexing of said head portion adjacent said throat portion, the cross section of said head portion adjacent said throat portion with respect to the cross section of said shaft portion providing a greater degree of flexing of said head portion adjacent said throat portion than the flexing of said shaft portion and the cross section of said handle portion having the least degree of flexing than any other portion of said racket frame.

2. The combination of claim 1 in which said plastic material is polycarbonate resin reinforced with 10 to 20 percent glass filler.

3. The combination of claim 1 in which the base of said T-shaped cross section of said head portion includes apertures for strings of said racket, pairs of adjacent ones of said string apertures having raised guides therebetween to receive a racket string from one side of said head portion through one of said apertures, around one of said guides and through the other of the pair of said apertures.

4. The combination of claim 3 in which said guides have circular peripheries about which the racket string may pass.

5. The combination of claim 1 in which the surface of said handle is textured to facilitate manual gripping thereof.