June 12, 1962 H. w. GROvEs 3,038,830 METHOD OF' MAKING A PRESTRESSED BOW Filed NOV. 16, 1959

INVENTOR Haro/dw. Groves BY 3,933,836 United States Patent() ” ICC Patented June l2, i962 1 2 FIGURE 3 is an elevation of the completed bow, as 3,533,830 held in the braced position by the string, and METHOD 0F MAKING A PRESTRESSED FIGURE 4 is an elevation from the back of the com ARCHERY BOW pleted bow. Harold W. Groves, 40S Virginia Ave. SE., Albuquerque, N. Mex. Referring now to FIGURE l, the bow is built up from Filed Nov. 16, 1959, Ser. No. 853,396 a backing 1 of glass cloth impregnated with a cured thermo 1 Claim. (Cl. 156-160) Y setting resin bonded to a wood core 2 by a urea or epoxy resin glue. The strips are clamped to form F1 The present invention relates to archery bows, and deals by clamps (not shown) while the glue is wet, and the particularly with archery bows which are prestressed prior 10 assembly is heated to set and cure the glue. The clamps to use. . Y are then removed, and the two-part assembly substantially » In modern archery, considered either as a pure sport retains the shape of the form. such as target shooting or as a useful pursuit such as This assembly is then removed from form F1 and forced game hunting, there are a number of features which onto form F2, as indicated in FIGURE 2, in the course should be characteristic of a high quality bow. A good of which backing member 1 is stressed in tension and core bow should cast at high velocity. Itshould be 2 is stressed in compression. The facing or belly layer consistent, i.e., cast successive arrows over identical tra 3 is the same type of glass cloth as is used for layer jectories under identical draws, and should cast 1 and is next añiXed to the assembly. any with a velocity varying directly with the amount Hardwood handle riser 6 and wooden end wedges 5, of draw. It should also have great durability, maintain 20 are wetted with glue and laid against the core 2. The ing its accuracy and ability to cast arrows at high velocity outer surfaces of the core 5, handle riser 6 and wedges after extended periods of use in all types of' weather. 5 are spread with glue and the belly layer of glass cloth Finally, operation of the bow should not unduly be laid against these surfaces. The assembly is clamped and fatiguing to the archer, even after hours of continuous heated as before. When the glue has been set, the clamps use. 25 are removed. The three layer assembly retains the shape l-t is the primary object of the present invention to pro­ Of the final form F2. Handle riser 4 may, if desired, be vide an archery bow having such desirable characteristics. made of two contrasting woods to achieve a decorative More specifically, an object of the present invention is effect. . to provide an archery bow capable of imparting higher _ It should be noted that the construction of bows, in velocities to arrows than prior art bows. 30 accordance with the present invention, results in a com Another object is to provide a bow having a uniform plete heavy center section 13, essentially unyielding, and draw-force characteristic up to and even well beyond » afpair of highly >iiexible limbs 12, the latter having an the usual full draw length. v average thickness of about 3/16 inch. A further object is to provide an archery bow requiring The wid-th of the laminated bow is then reduced or less force per unit draw when the bow is flexed through 35 tapered from a maximum at the handle to a blunt tip at the last increments of full draw than prior art bows of each end (FIG. 4), the extent of such -taper varying some comparable draw force at full draw. ‘ what with the draw force for which the particular bow Another and further object is to provide such a bow is designed by methods well known to bow designers. 'Ihe having greater durability and less weight than prior art center of the bow is cut to provide an arrow rest 7 and bows. 40 a handle grip 8, and the ends are nocked at 9 for the string The above and other objects are accomplished with bows loops, as indicated in the back elevation of FIGURE 4. of the present invention by „providing a laminated struc The bow is then given a final smoothing and varnish ture having a novel prestressed’structure which makes treatment. possible a considerable reduction in limb thickness, bulk VIn use the bow is flexed to the braced position and the and weight of A,such bows. `The prestressing method of 45 string 10 is added, as indicated by the dashed lines in the present invention, _together with the reduction in limb FIGURE 3. In comparison with the stresses in the un thickness, makes the resulting bows smooth drawing up braced position, `such iiexing increases the compressive to and above the normal full draw, makes it possible stresses in the facing layer 3, and increases the tensile to flex such bows through any number of consecutive cast stresses, in backing 1. The longitudinal fibers of core ing cycles without breakage or. letdown, and tremendously 50 2>adjacent to backing 1 acquire an increase in compression reduces the muscle strain normally experienced by -an while the compression in the fibers adjacent facing 3 is archer in a long shooting session. It also increases the reduced, the end condition of the stress in these fibers archer’s accuracy by reducing the trajectory error of his probably being one of tension. The neutral plane of the shots, for the reason that a draw which deviates by a braced bow lies somewhere in the core between its inter 55 small amount due to human error from -the desired full faces wi-th the backing and the facing. It should be noted that one result of the above-de draw causes only a small deviation from the desired arrow scribed prestressing is a condi-tion of safety for the archer. velocity. An identical deviation in draw length in many If the bow should break when the string is drawn, it will of the prior art bows, requiring as they do, much larger be much more likely to fracture the backing before the increments in draw force at the end of the draw than at 60 facing, as the greatest stress is in the backing. the beginning, causes a large deviation in arrow velocity A nocking point 11 may be provided by a knot in and hence a large trajectory error. string 10 to insure that an larrow may be readily lined The present invention will be more readily understood up with arrow face 7 for accurate center shot casting. by referring to the accompanying sheet of drawings, in This provision is particularly useful in game hunting, as which: 65 it enables the archer to select an arrow from his FIGURE l is a side elevation illustrating 4the bow of the and line it up in the bow without losing sight of his present invention in the first steps of assembly, with the quarry. backing strip and core on the prestress form, Suitable materials, dimensions and process variables FIGURE 2 is another side elevation showing all three are listed below ‘for a bow measuring 68 inches from tip laminations, including the facing, assembled on the final 70 to tip along the contour of the bow. These are not in form, together with the handle riser and end wedges, tended to be limiting, as `such bows may be built in any 3,038,830 É» preselected length and with a wide variety of draw forces described bow is 23% thinner in limb thickness than is an at full draw. equivalent bow without prestressing. The result is a re Backing and facing: 68" x 2" x .U50-.060" glass fiber duction in fatigue to the archer, «both because of the cloth impregnated with polymerized epoxy resin. lighter weight and the uniformdraw described above. In Core: 68" long strip of maple, 2” Wide, 01.135" thick at addition, a tremendous increase in durability is obtained the center tapered .002” per »longitudinal inch to each over prior art bows. The thinner limbs of the present end. bow are very flexible and have no known point of failure Handle riser: Maple, oak, or other hard wood. through repetitive cycling. They may be ñexed to draw End wedges: 6” long x 2" wide, 1/8” thick at bow end lengths up to 46 inches without breakage. tapering to zero. Maple or other hard wood. 10 The above description is to be considered as illustra Radius r, of FIG. `1: 4 inches. tive, and not limiting the invention of which modifications Circumference C of FIG. 1: 20 inches. may be made without departing from the scope of the in Radius r2 of FIG. 2: 8 inches. vention as set forth in the appended claim. Radius r3 of FIG. 2: 60 inches. What is claimed is: Thickness (maximum) of handle riser (FIG. 2): 3% A method of fabricating a prestressed archery bow inches. having the characteristics of high casting velocity, uni Length of l`handle riser, tip to tip (FIG. 2): 31 inches. form draw-force, and great durability, comprising the Glue: Urea resin or epoxy resin base. steps of applying a glue between a backing lamination of Heat treatment on each form: 190° F. for 2 hours. resin impregnated glass liber cloth and a core lamination ïìraw force: 42 pounds at 28 inches. of flexible Wood, clamping said laminations to a iirst form having an essentially hat center section and asymptoti Using the above-described bow at a standard 28” draw, cally joining convex end sections of equal and relatively 20 arrows weighing `40() grains each were cast at ve small radii until said glue sets, said laminations being suf loci-ties ranging `from 198 to 210 feet per second, as meas ficiently long to extend around at least half the circum ured with an electronic chronograph. An identical num 25 ference of each end section of said first form and being "...n ber of tests with identical arrows cast by three prior art held against said form with «said backing in contact there bows requiring the same draw force at 28 inches in with, ñtting such bonded lamination to a second form dicated, for such conditions, 160-172 ft./sec. for bo-w A, having a symmetrically disposed center section of a 145-165 ft./sec. `for bow B, and 145-163 tit/sec. for curvature to accommodate a rigid hardwood handle riser bow C. 30 of bi-convex cross section, said handle riser having front The 68-inch bow of the present invention has a linear and back surfaces meeting asymptotically at each tip, draw force characteristic up to and well beyond the stand said center section of said second form. having convex ard full draw of 28 inches. There is no tendency towards end sections of larger radius than said end sections of said nonlinearity or “stacking up” detectable below a »draw of ñrst form, gluing such a handle riser to said center sec 36 inches. This linearity between draw yforce and draw 35 tion on said second form and gluing a facing layer of length is particularly important in avoiding or minimiz resin impregnated glass fiber cloth to said core lamina ing trajectory errors. Thus, with the 42 pound bow of tion and said handle riser, said laminations and handle lthe present invention, a force of 11/2 pounds is required riser being rigidly clamped to said form during the set for each inch of draw up to and beyond 28 inches, while ting of said glue with said backing lamination facing in in comparable prior art bows the force required may in 40 ward. crease from 11/2 pounds per inch at the start to 4 pounds per inch at 28 inches. It is apparent that a draw which References Cited in the ñle of this patent is 1/2 inch short of Áfull will cause an error of BÃ1 of a UNITED STATES PATENTS pound in the draw force of the bow of the present in vention and that the corresponding error using the prior 45 2,100,317 Hickman ______Nov. 30, 4‘1937 art bow is 2 pounds, with corresponding errors in arrow 2,316,880 Miller ______Apr. 20, 1943 velocities and trajectories. Such errors are especially 2,665,678 Bear ______Jan. 12, 1954 likely to be committed in the usel of prior ant bows which 2,815,015 De Giacomo ______Dec. 3, 1957 stack up at full draw, in particular after prolonged use, 2,842,113 Roper ______July 8, 1958 as the lfatigued archer is prone to draw short under these 50 2,945,488 Cravotta et al. ______July 19, 1960 conditions. Another important advantage of the present bow is the OTHER REFERENCES reduction in thickness made possible by prestressing in “Archery,” for September l1957, pages 12, 13 and A59 accordance with the teachings herein. Thus, the above cited.