US3598410A

US3598410A - Filament wound structure and method of making same

Info

Publication number: US3598410A
Application number: US798306A
Authority: US
Inventors: Nick Costopoulos
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-02-11
Filing date: 1969-02-11
Publication date: 1971-08-10
Anticipated expiration: 1988-08-10

Abstract

A wooden bowling pin core has a continuous helical groove cut into the surface thereof. The groove begins near the bottom of the core, has a smooth transition between its sides and its bottom spirals upwardly about the pin at about 10 revolutions per inch and terminates near the top of the core. A nylon roving filament comprised of a plurality of individual unbonded fibers is fastened at the lower end of the groove and wound therein around the pin at about 30 pounds of tension until it reaches the top portion of the groove where it is fastened. The ratio of the cross sectional area of the groove to the cross sectional area of the thusly wound filament is about 0.55. The filament fibers are not bonded nor is the filament itself bonded to the surfaces of the groove. Hence, when stressed, the filament and its fibers are permitted to undergo limited sliding motion within the groove. In this manner, impact on any portion of the pin is more evenly distributed so as to result in a considerable increase in pin life. If desired, after the filament is wound and fastened, it is annealed at about 150* F. and then permitted to cool. The entire structure is then dipped in a suitable plastic coating material of a type having a limited tendency toward chemical or other bonding with the filament. The coated pin is then fitted with a conventional nylon sleeve or tube having a predetermined denier fineness gradient. If desired, this sleeve can also be annealed at about 150* F.

Description

United States Patent [721 inventor Nick Costopoulos Hartville, Wyo. [21] Appl. No. 798,306 [22] Filed Feb. 11, 1969 [45] Patented Aug. 10, 1971 [73] Assignees Darrell L. Oife Salt Lake City, Utah William R. Jones Wheatland, Wyo. part interest to each [54] FILAMENT WOUND STRUCTURE AND METHOD 01- MAKING SAME 25 Claims, 6 Drawing Figs.

[52] US. Cl 273/82 R, 273/72, 273/D1G. 6, 273/156 [51] Int. Cl. A63d 9/00 [50] Field of Search 273/72, 77, 80, 82,D1G. 7; 117/8; 161/47; 156/172, 189

[56] References Cited 7 UNlTED STATES PATENTS 780,244 l/l905 Truesdell 273/72 1,585,857 5/1926 Hedenskoog. 273/82 2,944,821 7/1960 Mason 273/82 3,152,804 10/1964 Costopoulos... 273/82 3,257,113 6/1966 Medney 273/82 PLASTIC COATING Primary Examiner- Richard C. Pinkham Assistant Examiner-Richard J. Apley Attorney-Griffin, Branigan and Kindness ABSTRACT: A wooden bowling pin core has a continuous helical groove cut into the surface thereof. The groove begins near the bottom of the core, has a smooth transition between its sides and its bottom spirals upwardly about the pin at about 10 revolutions per inch and terminates near the top of the core. A nylon roving filament comprised of a plurality of individual unbonded fibers is fastened at the lower end of the groove and wound therein around the pin at about 30 pounds of tension until it reaches the top portion of the groove where it is fastened. The ratio of the cross sectional area of the groove to the cross sectional area of the thusly wound filament is about 0.55. The filament fibers are not bonded nor is the filament itself bonded to the surfaces of the groove. Hence, when stressed, the filament and its fibers are pennitted to und e rgo limited sliding motion within the groove. in this manner, impact on any portion of the pin is more evenly distributed so as to result in a considerable increase in pin life.

if desired, after the filament is wound and fastened, it is annealed at about 150 F. and then permitted to cool. The entire structure is then dipped in a suitable plastic coating material of a type having a limited tendency toward chemical or other bonding with the filament. The coated pin is then fitted with a conventional nylon sleeve or tube having a predetermined denier fineness gradient. If desired, this sleeve can also be annealed at about 150 F.

PATENTEUAUGIOIHH 3,598 410 sum 1 OF 2 I60 FIG. I '2 PLASTIC COATING mvnmon NICK COST OPOULOS NYLON ROVING By griffin, 3W)! an) 9011M;

ATTORNEYS PATENTEUAUBIOIQH 73.598410 SHEET 2 BF 2 INVENTOR NICK COSTOPOULOS ATTORNEYS FILAMENT WOUND STRUCTURE AND METHOD OF MAKING SAME In the reissue patent, I disclose a bowling pin having a plurality of annular grooves about its surface. A plurality of layers of nylon filament are wrapped around the surface and bound thereon by a plastic matrix so that the first layer of filament is primarily located within the grooves; and each remaining layer offilament is wound and held about the pin at a different angle to the pins axis. Thatpin was found to have a life of more than twice that of the best plastic-coated pins previously available.

One of the problems of the above noted type of pin which has a plurality of fiber layers wound thereon is that its manufacture is time consuming and therefore expensive. In addition, in order to meet the rigid standards required for Official Bowling Pins, the thickness of each layer of matrix material has had to be rigidly controlled. Hence, it is an object of this invention to provide a core for a bowling pin that has the longlife properties of the type constructed in accordance with my reissue patent, but wherein such qualities are obtained by only a single layer of filament.

Previously, the grooves on mass-produced bowling pins or other wooden core structures such as baseball bats, shovel handles, fiagpoles, or the like, have been placed thereon by spinning the wooden core about its axis and simultaneously cutting a plurality of annular grooves into the surface of the core. Hence, when the first layer of filament is wound into the grooves, it must either cross over the cores outer structure to pass from one groove to another; or a separate operation has been required to cut communicating passages between the grooves. In either event, the filament has had to undergo a relatively sharp transition as it passed from one groove to another. This has led to localized stresses within the filament so that it has had a tendency towards breakage at the crossover point. Also there has been a tendency for air to be trapped in the binding matrix at the crossover point and this has led to dimensional instability, surface irregularities, and further stress concentrations. Hence, it is another object of this invention to provide amethod of producing a filament wound core which substantially eliminates the surface irregularities and stress concentrations.

Many wooden cored structures have been made of solid hard wood such as hickory, ash, or maple. This is particularly true of baseball bats and bowling pins because certain strict standards therefor have been set forth by national associations. In relatively recent years, however, laminated structures have been sanctioned and, therefore, have been extensively used. This has permitted the use of smaller pieces of wood, but has still required the use of only high quality wood in order that the finished product meet strength requirements. It is another object of this invention to provide a method of making such a wood cored structure which permits the use of lower quality laminae while still maintaining strength requirements.

Laminated wooden baseball bats and bowling pins in particular have usually had the various laminae joined together in lamination planes which are parallel to the structures main axis; and it has been at these lamination planes where the pin and bat failures have most frequently occurred. In this respect, it is believed that such failures occur either through shear stresses acting along the lamination planes; or through tension stresses resulting from shocks-which travel from a point of impact across the core, perpendicular to the lamination planes, to the plane of fracture; or, of course thru combinations of such shear and tension stresses. It is another object of this invention to provide a method of winding a reinforcing filament on the core of such a structure so as to obtain a more even distribution of the forces causing these shear and tension stress failures.

As a wooden core is machined so as to provide the desired contour to its surface, many of its fibers are cut so that the thusly cut ends thereof are exposed on the surface of the core. This is particularly significant in bowling pins where the fiber ends are exposed at the ball line so that, through use, they become crushed and softened at the ball line region so as to result in a rapidly decreasing bowling pin quality-standard known as scoreability". That is, the ability of a pin (or more properly a set of ten pins) to consistently react in the same manner to the same type of impact. In other words, the scoreability of a set of pins is a measure of that set's ability to repeatedly produce the same bowling score when a bowler (or a testing machine) rolls balls in the same manner. It is another object of this invention to provide a method of reinforcing a bowling pin so that the exposed fiber ends at the ball line are less susceptible to softening so that the pins scoreability standards are maintained at a high level for a longer period of time.

In addition to the type of structure described in my reissue patent, other types of filament wound wooden core structures are also available. Examples of these structures are described in U.S. Pats. No. 3,402,932 to Conklin et al; 3,257,113 to Medney; and 3,135,639 to Bilodeau. These structures, however, have used layers of filaments on selected areas on the cores surface, such as at the ball line of a bowling pin; and these filaments have been held in place by cured resins or the like. Among other shortcomings, however, these devices have not had a uniform weight distribution and, therefore, are sometimes undesirable for this reason. Similarly, because of its many plastic matrix layers, it has been difficult to control the weight distribution on structures such as the pin described in my reissue patent. Hence, it is another object of this invention to provide filament wound cores for bowling pins and baseball bats, or the like which have a more uniform weight distribution.

In accordance with the principles of the invention, the wooden core that is to be reinforced is continuous spirally grooved over a major portion of its surface. A roving type of filament is then fastened at one end of the groove and wound therein under tension so as to spiral along the groove and about the wooden core. It is then fastened at the other end of the groove, but there is no other appreciable bonding or affixing of the filament to the surfaces of the groove. In this manner, the filament is permitted to undergo limited sliding motion whereupon, an impact force at one portion of the cores surface is transmitted to the filament which, by virtue of its ability to slide within the groove, transmits some of the impact force to other portions of the groove so as to more evenly distribute the stresses caused by the impact.

The foregoing and other objects, features, and advantages of this invention will be apparent from the more particular description of preferred embodiments thereof as illustrated in the accompanying drawings wherein the same reference numerals refer to the same parts throughout the various views. The drawings are not necessarily intended to be to scale, but rather are presented so as to illustrate the principles of the invention in clear form.

In the drawings:

FIG. 1 is an elevational view illustrating a core for a bowling pin embodiment of the invention. Therein, a portion of a finished pins coating is broken away from a part of its surface so as to expose the wooden core;

FIG. 2 is a cross-sectional view of the FIG. I embodiment taken along the lines 2-2 thereof;

FIG. 3 is an enlarged partial cross-sectional view ofthe FIG. I embodiment taken along the line 34 thereof;

FIG. d is a cross-sectional view of a multiroving type of filament illustrating the individual fibers of such rovings;

FIG. 5 is an elevational view partially broken away to illustrate application of a-finishing sleeve which, if desired, can be applied over the core described in connection with FIG. 1; and,

FIG. 6 is an elevational view similar to that of FIG. I but illustrating a baseball bat embodiment of the invention.

In FIG. 1, a wooden core is comprised of a plurality of individual laminae 12 as indicated in FIG. 2. The core has a major axis 14; a plurality of minor axes such as 16 which are perpendicular to interior lamination planes such as 18; and a plurality of minor axes 20 which are parallel to the interior lamination planes [8.

A continuous groove 22 is cut or otherwise formed in the surface of the core 10 extending from a point 24 located about a half inch up from the bottom of the core 10 so as to spiral upwardly in a helix about the surface of the core and terminate at a point 26 about A of an inch from the top of the core. In the past, such as is described in my reissue patent, a plurality-of individual grooves have been cut into the surface of a wooden core, because, in that manner, the entire surface of the core could be grooved in one operation. Moreover, such grooves have had sharp substantially perpendicular joints where the bottoms of the grooves met the sides. l have found that individual grooves having sharp transitions between the sides and the bottoms thereof are not as satisfactory as those about to be described. In this respect, as shown in FIG. 3, the groove 22 has a smooth transition surface 28 between the

sides

30 and 32 and the bottom 34 thereof.

The groove 22 can be cut into the surface of the core by means of a traveling nut type of lathe. This however, is a time consuming operation and not suited to mass production. Hence, it is preferred that the groove be rolled or pressed onto the surface of the core in much the same manner as are threads of some types of mass produced bolts or screws. That is, the entire thread is impressed on the cores surface in one simultaneous operation, such as by pressure dies which substantially enclose the core. in this manner, it is not necessary for a cutting tool to begin at one end of the core and progressively traverse its length while the core is rotated.

A filament 38 comprised of four multifiber rovings 40 has one end thereof fastened in the groove 22 by means of a wooden peg 42 which is wedged and glued into a predrilled hole 44. In this respect, it should be noted that a roving is to be distinguished from a cord in that the individual fibers comprising the roving element are not twisted, nor is the roving itself twisted. In a cord, on the other hand, the individual fibers and/or the strand itself are twisted. It should be also noted that the rovings are comprised of unbonded fibers; and the rovings themselves are not bound together. This aspect of my structure will become more meaningful shortly.

After the end of the filament 22 is fastened by peg 24, it is placed under a tension of between 10 to 50 pounds. I have found, however, that 30 pounds is an optimum tension. As tension approaches 50 pounds, the transition areas of the groove tend to become deformed and the filament has a tendency to break. As the tension drops below 30 pounds, the benefits of my invention begin to decrease until, at about 10 pounds, the benefits have almost diminished.

While the filament is held under tension, the core is rotated so that the filament is spiralled upwardly within the groove 22. When the filament reaches point 26, it is fastened to the core by means of another wooden peg, not shown, in the same manner as was discussed in connection with the other end of the filament. As has been noted, the filament is comprised of individual rovings which, in turn, are comprised olabout 120 end count fibers" as shown in FIG. 4. Filaments of this type are readily commercially available in a variety of sizes. For purposes of illustrating the invention, however, l used a filament having a cross-sectional area of 8.4 l0' square inches; and the groove 22 has a cross-sectional area of l5.3 l0 square inches. The reason these dimensions are illustrated is because I have found that I obtain best results when using a groove-fill ratio of about 0.55. That is, the ratio of the crosssectional area of the groove to the cross-sectional area of the filament. Groove-fill ratios of between 0.25 and 0.95 have produced beneficial results, but, as noted, a ratio of 0.55 is preferred. There is a possibility that this figure might vary depending upon the number of times the groove 22 circles the core 10 between the time it leaves point 24 and reaches point 26. In this respect, the 0.55 ratio appears to be the preferred value for a groove pitch of 10 revolutions per inch.

In one bowling pin embodiment it was found to be desirable I to vary the pitch of the groove as the groove progressed along the surface of the core. In this respect the pitch varies from about eight grooves per inch at the base of the pin to about 10 grooves per inch at the ball line, and then varies to about 8 grooves per inch in the transition area between the ball line and the neck to about 10 grooves per inch at the neck, and then varies to about 8 grooves per inch extending to the top of the pin. Among other advantages this embodiment permits more filament to be added to the surface of the core in the more critical stress areas and at the same time a lesser amount of filament is used in the noncritical areas, thus reducing the cost of manufacture and substantially increasing the strength in the desired areas.

Similarly, there is a possibility that the preferred groove-fill ratio may vary somewhat with the depth of the groove as well as its cross section. In this respect, in the illustrated embodiment, the grooves depth is 0.0625 inches. Still further, as will be noted more fully shortly, there is a possibility that a thusly structured pin's scoreability might be affected by the core s land-groove ratio. That is, the ratio of the cores land area (the core surfaces between successive revolutions of the groove) and the projected surface area of the groove itself. This, of course, would have an influence upon the width of the groove and thereby the groove-fill ratio for a given depth. In any event, for 10 groove revolutions per inch; and a groove depth of0.0625, the preferred groove-fill ratio is 0.55.

In still another bowling pin embodiment it was found desirable to vary the depth of groove in the more critical areas ofthe core. In this respect the cores groove-fill ratio varied from about 0.35 at the base increasing to about 0.90 at the ball line; decreasing to about 0.35 in the area between the ball line and the neck; increasing to about 0.90 in the neck area; then decreasing to about 0.35 at the top of the core. This embodiment provides even greater impact resistance, thus substantially increasing the durability of the finished pin.

After the filament is wound and fastened, the ends thereof are trimmed; and the plugs such as 42 are smoothed to conform to the general surface of the core. If desired, the thusly reinforced core can be annealed and then cooled. This appears to more uniformly distribute the compressive forces of the filament upon the various groove surfaces with which it is in contact. Also, it appears that such annealing increases the tension in the filament itself. In this respect, although other annealing temperatures might be use, suitable annealing effects occur when the core is subjected to a temperature of about F. and then cooled.

After winding, and annealing, if desired, the core is coated with a plastic material so as to fill the grooves above the filament and extend about one-sixteenth of an inch outwardly of the core itself. It should be noted, however, that this plastic coating does not make a chemical bond with the filament or its individual fibers. lnasmuch as the filament is not otherwise bonded to the core, the filament is permitted to undergo limited sliding motion within the groove when subjected to impact. As noted above in connection with the discussion of the principles of the invention, this is important.

Previous filament wound cores have purposely resinbonded or otherwise bonded the filament to either the core itself or the outer plastic coating, or both. Hence, although the outer surface of the pin has been reinforced against impact, the full force of the impact is taken at the point thereof. With my structure, on the other hand, the forces at the point of impact are transmitted, by virtue of the ability of the filament to slide within the groove, to other portions of the core; and it is in this manner, that my present invention provides even better durability than the structure described in my reissue patent, while at the same time, requiring only a single application of the filament reinforcing thereon.

By using a single continuous groove, I have also eliminated the requirement that the filament either cross over the core 5 outer structure to pass from one groove to another, or, the requirement for cutting separate passages between the grooves; whereupon l have eliminated the localized filament stresses attendant with either such structure. Also, the abovedescribed structure eliminates the surface irregularities resulting from air being trapped under the plastic coating at the point where the filament crosses over from one groove to another.

It has also been noted above that the prior art pins have had a tendency to fracture at the lamination planes. With reference to FIG. 2, for example, a blow along axis might cause one of the lamination planes 18 to undergo a shear stress failure, and a blow along axis 16 at point 16a, for example, can cause a shock wave to travel across the pin and cause a tension stress failure of lamina 12a at lamination plane 18a. A thusly fractured conventional pin might simply fall apart; and, although a filament wound pin in accordance with the prior art might not actually fall apart, it could nevertheless undergo an undetected fracture. This, of course, would mean that the pin (or baseball bat as the case may be) would continue to be used and result in undesirable performance so that, in many respects, the fractures consequences would be worse than if the pin had not been filament wound to begin with. With the structure of the instant invention, however, an impact at point 16a for example, would be partially absorbed by the sliding motion of the filament within the groove so as to result in a distribution of the forces of impact about the entire surface ofthe core encompassed by the filament.

Similarly, by the ability of my core to distribute the forces of impact, it should be apparent that the end fibers at the point of such impact suffer less damage so that, in the case of a bowling pin, the scoreability is maintained at a high level for a longer period of time.

In accordance with still another aspect of my invention, l place a conventional nylon bowling pin sleeve or tube over the plastic-coated core 50 (FIG. 5). In this regard, I prefer to use a sleeve of the type having a denier fineness gradient having about 140 denier in the head of the pin and about 280 denier in the neck and ball lines thereof. A suitable fabric sleeve of this type is described in U.S. Pat. No. 3,184,236.

After the sleeve 52 is fitted over the core 50, the structure can once again be annealed, if desired, so as to distribute and increase the compressive forces of the sleeve. The entire structure can then be given a final plastic coating 56 as illustrated in FIG. 5, and finished in a conventional manner.

It has already been noted that although the invention has been described in connection with a bowling pin, it finds utility in connection with other wooden-cored structures as well. In connection with a baseball bat, for example, the invention has particular utility. Because of this fact, therefore, I will now briefly discuss application of my invention to a core for such a bat.

As illustrated in FIG. 6, a bat core 60 has a groove 62 extending from a point 64 near the flared portion of the handle so as to spiral upwardly in a helix about the surface of the core and terminate at a point 66 near the end of the bats core. Except for possibly desirable minor variations in the land-groove ratio, the baseball bat core is constructed in a similar manner as was the bowling pin core. The particular advantage of my invention in connection with a baseball bat, however, relates to the length and function of the bat. That is, when the bat is impacted, it acts as a lever with the hitters hands as a fulcrum. Consequently, the main stresses on the bat occur at the point of impact on the one hand, and the effective fulcrum point on the other. When the core of such a bat is wound in accordance with the teachings of my invention, however, part of the force of the impact is transmitted to the filament causing it to slide within the groove and effect a further reinforcement of the handle area. Consequently, the force of the impact has a tendency to increase the strength in the bats handle rather than to reduce it.

The above described bowling pin was tested by a major United States independent testing laboratory under league bowling conditions at two different locations. Two hundred pins were each tested for over 2,000 lines of bowling. The test results showed no variance in the scoreability of the pins.

Hence, even though the pins were subjected to 2,000 lines of bowling, they still complied with the scoreability requirements for new tournament-quality pins. The same tests indicated that durability exceeded minimum requirements. In fact, u'nder open bowing conditions, 40 pins were tested for in excess of 10,000 lines without a single failure. The average pin on the market today, on the other hand, withstands only approximately 4,000 lines of bowling before replacement is required; and in fact, it is rare for any given pin to withstand 8,000 lines. Hence, it will be apparent, that the structure of my invention indeed produces dramatic results.

Similarly, although a testing program on the baseball bat embodiment has not yet been completed, one college baseball team that has used bats according to the invention has thus far characterized such bats as being unbreakable. That is, there has been no structural failure in a bat subjected to testing to date.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention. For example, although the invention has been described in connection with a groove and filament spirally extending over substantially the entire length of the core, this is merely desirablenot required. In fact, as was noted in connection with the baseball bat embodiment, breakage thereof was substantially reduced below normal breakage even though some bats core were only grooved and wound in the handle area. Similarly, although it is preferred to groove and wind substantially the entire length of the core of bowling pin embodiment, improved results can be obtained by only grooving and winding the core in selected areas, such as, for example, at the ball line. Also, it may be desirable for one reason or another to fasten the filament at selected intermediate points along the groove.

The embodiments of the invention in which an exclusive property or privileges are claimed are defined as follows:

I claim:

1. In an elongated wooden structure having a substantially solid wooden core along an axis thereof, the combination comprising:

a substantially continuous groove extending from a first point on the surface of said core substantially spirally about said axis to a second point on the surface of the core;

a continuous length of filament located in said groove, said filament being in a state of tension and extending from said first point to said second point; and,

an outer coating contiguous to said core and covering said core and said filament, said coating being substantially unbonded to said filament, whereby said filament is substantially unbonded to either said core or said outer coating and is thereby adapted to undergo limited sliding motion with respect to both said groove and said coating.

2. The structure of claim 1 wherein said filament is comprised ofa plurality ofindividual fibers.

3. The structure of claim 1 wherein said filament is comprised of unbonded fibers comprising a roving.

4. The structure of claim 1 wherein said groove, having two sides and a bottom thereof has a smooth transition between said sides and said bottom so that the surface of said filament abutting the bottom and sides of said groove is maintained in an arcuate configuration.

5. The structure of claim I wherein the groove-fill ratio is between 0.25 and 0.95.

6. The structure of claim 5 wherein the groove-fill ratio is about 0.55.

7. The structure of claim 1 wherein said groove has characteristics resulting from being pressed into the surface of said core.

8. The structure of claim 1 wherein the pitch of said groove is greater at one of said first and second points along said surface of said core than at a portion along said surface intermediate said first and second points.

9. The structure of claim 8 wherein said core has the shape of a bowling pin, having a base portion and a ball line portion, and a neck portion and a transition portion between the ball line portion and the neck portion, and a head portion; and wherein the pitch of said groove is smaller at said ball line portion and said neck portion than at said base portion and said head portion and said transition portion.

10. The structure of claim 9 wherein the pitch of said groove at said base portion and said transition portion and said head portion provides about eight grooves per inch, and the pitch at said ball line portion and said neck portion provides about 10 grooves per inch.

11. The structure of claim 9 wherein the groove is deeper at a first portion on said surface on said core than at a second portion thereof.

12. The structure of claim 11 wherein said groove depth decreases from about 0.0625 inches at said base portion to about 0.03125 inches at said ball line portion and increases to about 0.0625 inches at said transition portion, and decreases at said neck portion to about 0.03125 inches and increases to about 0.0625 inches at said head portion.

13. The structure ofclaim 8 wherein said core has the shape of a ball striking instrument, having an elongated handle portion and a ball striking portion, and a transition portion between said handle portion and said ball striking; and wherein the pitch of said groove is larger at said handle portion and said ball striking portion than at said transition portion.

14. The structure of claim 13 wherein the pitch of said groove varies to provide about eight grooves per inch at said handle portion and said ball-striking portion and about 10 grooves per inch at said transition portion.

15. The structure of claim 13 wherein the groove is deeper at a first portion on said core than at a second portion thereof.

16. The structure of claim 15 wherein the depth of said groove varies from about 0.03125 inches at said handle portion and said ball striking portion to about 0.0625 inches at said transition portion.

17. A method of making a filament reinforced wooden cored structure comprising the steps of:

grooving the surface of said core to form a substantially continuous spiraled groove extending from a first point on the surface of said core to a second point on the surface of said core;

fastening an unbonded filament at said first point;

placing said filament under tension;

winding said filament in said core while said filament is held under tension;

affixing said filament in said groove by fastening said filament to said core at said second point so that said filament is adapted to undergo limited sliding motion within said groove; and,

applying an outer coating contiguous to said core end covering said core and said filament so that said coating is substantially unbonded to said filament whereby said filament is permitted to undergo limited sliding motion with respect to both said groove and said coating.

18. The method of claim 17 wherein said winding step includes:

winding said filament in said groove to obtain a groove-fill ratio of between about 0.25 and 0.95.

19. The method of claim 17 wherein said groove has two sides and a bottom thereof and includes the step of smoothing the surface of said groove between said sides and said bottom so as to form an arcuate surface therebetween.

20. The method of claim 17 wherein said grooving step includes the step of pressing said groove into the surface of said core.

21. The method of claim 17 including the step of annealing said filament after it is fastened to more uniformly distribute the compressive forces of the filament upon the groove surfaces.

22. The method of claim 21 wherein said filament is annealed at about F. and then cooled.

23. The method of claim 17 including the step of covering said outer coating with a fabric sleeve.

24. The method of claim 23 including the step of annealing the sleeve-covered structure.

25. The method of claim 24 wherein said annealing step is conducted at a temperature of about 150 F.

Claims

1. In an elongated wooden structure having a substantially solid wooden core along an axis thereof, the combination comprising: a substantially continuous groove extending from a first point on the surface of said core substantially spirally about said axis to a second point on the surface of the core; a continuous length of filament located in said groove, said filament being in a state of tension and extending from said first point to said second point; and, an outer coating contiguous to said core and covering said core and said filament, said coating being substantially unbonded to said filament, whereby said filament is substantially unbonded to either said core or said outer coating and is thereby adapted to undergo limited sliding motion with respect to both said groove and said coating.

2. The structure of claim 1 wherein said filament is comprised of a plurality of individual fibers.

5. The structure of claim 1 wherein the groove-fill ratio is between 0.25 and 0.95.

6. The structure of claim 5 wherein the groove-fill ratio is about 0.55.

13. The structure of claim 8 wherein said core has the shape of a ball striking instrument, having an elongated handle portion and a ball striking portion, and a transition portion between said handle portion and said ball striking; and wherein the pitch of said groove is larger at said handle portion and said ball striking portion than at said transition portion.

17. A method of making a filament reinforced wooden cored structure comprising the steps of: grooving the surface of said core to form a substantially continuous spiraled groove extending from a first point on the surface of said core to a second point on the surface of said core; fastening an unbonded filament at said first point; placing said filament under tension; winding said filament in said core while said filament is held under tension; affixing said filament in said groove by fastening said filament to said core at said second point so that said filament is adapted to undergo limited sliding motion within said groove; and, applying an outer coating contiguous to said core end covering said core and said filament so that said coating is substantially unbonded to said filament whereby said filament is permitted to undergo limited sliding motion with respect to both said groove and said coating.

18. The method of claim 17 wherein said winding step includes: winding said filament in said groove to obtain a groove-fill ratio of between about 0.25 and 0.95.

22. The method of claim 21 wherein said filament is annealed at about 150* F. and then cooled.

25. The method of claim 24 wherein said annealing step is conducted at a temperature of about 150* F.