US3156230A

US3156230A - Takedown bows

Info

Publication number: US3156230A
Application number: US63551A
Authority: US
Inventors: Harold W Groves
Original assignee: Individual
Current assignee: Individual
Priority date: 1960-10-19
Filing date: 1960-10-19
Publication date: 1964-11-10
Anticipated expiration: 1981-11-10

Description

. Nov. 10, 1964 H. W. GROVES TAKEDOWN BOWS Filed Oct. 19, 1960 United States Patent 3,156,239 TAKEDQWN BOWS Harold W. Groves, 1821 Somervell St. NE., Albuquerque, N. Mex. Filed Get. 19, was, Ser. No. 63,551 2 Claims. (CL 124-23) This invention relates to two piece demountable, or as they are more commonly known, takedown archery bows. More particularly, this invention is directed to a two piece scarf jointed takedown archery bow.

Archery bows have a length about equal to the height of the archer with the result that the bow is an awkward and cumbersome object to carry or transport. Nevertheless, the rigidity of the middle part of a bow is so essential that no jointed bow has hitherto met the requirements of the art to the extent of finding favor with demanding archers. This rigidity must be obtained in a joint which is easy to assemble with automatic alignment of the two parts. The joint must be so strong that there will be no detectable flexing at full draw or any other time. In addition, the mechanism provided for joining the two bow parts must not require any modification in the shape of the bow and it must not add any appreciable or discernable weight to the bow.

The objective of this invention is to provide an archery bow which meets all the foregoing requirements. The manner in which this is accomplished will be clearly understood from the following description having reference to the drawing which is made a part of this specification and in which:

FIGURE 1 is an outline showing of the disjointed bow and the parts provided for alignment and securing.

FIGURE 2 is side fragmentary view partly in section showing the bow joint assembled but not tightened.

FIGURE 3 is a view similar to FIGURE 2 but showing the joint fully tightened.

Referring to the drawing, FIGURE 1, a completed bow having the joint of this invention is shown in exploded view. A scarf joint is provided between limbs A and B in the riser portion and just below or in the lower part of the handle and lying in a plane which fore and aft inclines downwardly from the belly side to the back side and which from side to side is normal to a median line through the limbs.

Provision for precision alignment of the two bow limbs is made by a pair of leader pins mating in accurately located opposed

sockets

13 and 15. The leader or pilot pins 11 are desirably permanently afiixed in one of their respective sockets. A threaded socket 17 is provided in the upper limb approximately in the center of the joint to cooperate with a cap screw 19 seated in a bore 21 and counter bore 23. Provision is made in the configuration of the joint as will be seen in the more detailed showing of FIGURE 2 such that when the joint is assembled and tightened for use it is absolutely rigid with no discernable flexing or working whatever.

Referring now to FIGURE 2, a more detailed showing of the joint designated generally by the numeral 9 is made. This joint lies symmetrically about the median plane it). The following description has particular reference to the built up laminated bow comprising an inner core of wood and outer layers of glass fiber or glass cloth. Many of such bows are custom made to a particular order specifying size and draw. Where this is the case, the bow must be in essentially completed form before the joint may be made. The first step in processing the joint is to lay out on the finished bow blank the proper angle for the saw cut to part the bow. The bow is next mounted in a drilling device such as a drill press with the angle of the joint line at right angles to the drill. The bore is made in the approximate center of 'ice the contemplated joint and is started on the surface of the nether limb. The bore is drilled to a depth approximately on the opposite side of the joint plane. The values herein given are not intended to be limiting but have been found to be adequate in practice for a 66 inch bow of 40 pound draw. The center bolt is of inch diameter and has a length of 1 /2 inches in the stem portion. The center bore is therefore of inch diameter in this embodiment.

The bow blank is next counter bored to a depth of inch to allow for a receiving recess for the cap screw head as shown at 19 and 23 in FIGURE 2.

The bow blank is next removed from the drilling device and is accurately parted on the previously marked joint plane by a sawing operation. The bore in the upper or handle limb is enlarged and tap-threaded to cooperate with a threaded metal insert 2-5. The threaded receptacle in the bow blank is provided with a layer of strong adhesive which has great binding strength to both wood and metal such as an epoxy resin. The bushing is promptly screwed into the receptacle and the adhesive allowed to set.

The opposing surfaces of the joint are next provided with glass fiber plates. Thecombined thickness of these plates is equal to the width of the saw kerf made during the sawing operation. The butt plates are obtained by cementing a glass fiber layer of cloth to each limb joint portant feature of my improved joint in that it is the means by which Working and flexing in the joint are prevented and the original characteristics of the bow are maintained.

The amount of hollow grinding necessary will depend upon the particular wood in the bow riser and the material of the butt plates. The amount of hollow grinding in any particular case can be determined with conventional engineering stress analysis with the criteria, however, that the joint must be closed, i.e., no gap must appear when the clamping bolt is properly tightened, and this amount of compression of the outer fibers of the bow limbs contiguous the joint on the back side of the bow must be at least equal to what the tension would be at full draw if no joint were present. This is equivalent to a pre-compression on the belly side of the joint such that it is equal at least to what it would have been at full draw if no joint were present and multiplied by a factor of two if the joint is present at right angles to the length of the bow and the joining bolt is in the middle. The reason for this is that the length of the moment arm in the joint is reduced to one half of its original length. As a matter of practice, it is not feasible to make a right angle joint and instead a scarf joint is utilized. The length of the moment arm, i.e., the distance between bolt and abutting surfaces of the bow limbs on the belly side is one half the thickness of the bow at the joint times the secant of the angle between the scarf and the direction of thickness of the bow at the joint. It is preferred that the angle of the scarf be at 45 degrees and accordingly the length of the moment arm is one half the thickness times 1.4 or more conveniently stated as .7 T where T stands for the thickness of the bow at the joint.

From the above analysis and a determination of the modulus of elasticity of the material abutting the joint, be it rosewood, beefwood or other hardwood, the amount of compression on the belly side at full draw can be readily determined and from this determination, the

J amount of hollow grinding necessary in the abutting surfaces of the joint is established.

It is desirable that the joint be hollow ground an amount which is in excess of the bare necessary extent and I prefer a safety factor of at least two in this respect. For example, in a thirty inch limb length in the nether limb of a forty pound bow having an overall length of 66 inches, I provide a hollow grind of 0.0075 inch and a like amount of hollow grinding in the abutting surface of the longer limb. The total clearance in this example is therefore 0.015 inch. This value allows for give or set in the material of the joint and the bolt socket and results in a joint of integrity for the life of the how.

The bow is next reassembled and clamped tightly by bolt 19, meanwhile making certain that the two sections of the bow are in perfect alignment at the joint. The bow is mounted in a drilling device such as a drill press with the plane of the joint at right angles with the drill. The two pilot pin sockets 13-15 are drilled and accurately reamed to a squeeze fit with the pins. The bow sections are next disassembled and the pins are forced into one set of the sockets so provided. A strong binding cement such as a urac or epoxy cement is previously applied to the sockets to which the pins are permanently afiixed. The second pair of sockets are lapped or carefully reamed to a snug slip fit with the remaining or free ends of the pins.

The bow joint is inconspicuous in the assembled bow as is seen in FIGURE 3. The open ends of the pin sockets are preferably plugged with hard wood plugs cemented in place. The bow blank is now ready for the final procedures such as adjusting, finishing and polishing as is the custom in the art.

While I have shown and described the fundamental novel features of the invention as applied to a preferred embodiment, it is understood that there may be various omissions and substitutions and changes in the procedures, forms and details in the making of and in the device illustrated by those skilled in the art without departing from the spirit of the invention. It is my intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.

I claim:

1. A takedown bow having two limbs joined in a riser section, a grip fitting handle portion in the middle of the riser section, said grip fitting handle portion being configured to the natural grip of the human hand, a scarf joint in said riser portion commencing proximate the handle portion lower end at the bellyface and extending through the riser section on a descending plane to the back face, said scarf joint being provided by a sawing operation of the unitary bow blank, a composition plate having a thickness equal to half the saw kerf afiixed to the joint surface of each limb, at least one of said plates being gradually diminished in thickness from the fore and aft end portions to the middle thereof, a clamp bolt seat in the bottom limb aligned with the perpendicular to the joint and being located in the middle of the joint substantially, a clamp bolt threaded socket afiixed in the upper limb and aligned with the bolt seat when the limbs are in assembled alignment, a pair of guide pin sockets transfixing said joint and located in the opposing surfaces of the limbs in spaced relation fore and aft the middle of the joint, a pair of guide pins adapted to seat in said guide pin sockets to align the limbs when assembled, and a bolt adapted to engage said bolt seat and bolt socket to compressedly join said limbs and said plates with consequent compression of the fore and aft outer portions of the limbs.

2. The takedown bow of claim 1 in which said scarf joint lies in a plane of degrees approximately to the direction of elongation of the bow.

References Cited in the file of this patent UNITED STATES PATENTS 114,138 Hersey Apr. 25, 1871 1,082,062 Aine Dec. 23, 1913 1,720,269 Fullerton July 9, 1929 2,228,823 Helm Jan. 14, 1941 2,353,134 Anderson July 11, 1944 2,457,793 Bear Dec. 28, 1948 2,514,638 Grenier July 11, 1950

Claims

1. A TAKEDOWN BOW HAVING TWO LIMBS JOINED IN A RISER SECTION, A GRIP FITTING HANDLE PORTION IN THE MIDDLE OF THE RISER SECTION, SAID GRIP FITTING HANDLE PORTION BEING CONFIGURED TO THE NATURAL GRIP OF THE HUMAN HAND, A SCARF JOINT IN SAID RISER PORTION COMMENCING PROXIMATE THE HANDLE PORTION LOWER END AT THE BELLYFACE AND EXTENDING THROUGH THE RISER SECTION ON A DESCENDING PLANE TO THE BACK FACE, SAID SCARF JOINT BEING PROVIDED BY A SAWING OPERATION OF THE UNITARY BOW BLANK, A COMPOSITION PLATE HAVING A THICKNESS EQUAL TO HALF THE SAW KERF AFFIXED TO THE JOINT SURFACE OF EACH LIMB, AT LEAST ONE OF SAID PLATES BEING GRADUALLY DIMINISHED IN THICKNESS FROM THE FORE AND AFT END PORTIONS TO THE MIDDLE THEREOF, A CLAMP BOLT SEAT IN THE BOTTOM LIMB ALIGNED WITH THE PERPENDICULAR TO THE JOINT AND BEING LOCATED IN THE MIDDLE OF THE JOINT SUBSTANTIALLY, A CLAMP BOLT THREADED SOCKET AFFIXED IN THE UPPER LIMB AND ALIGNED WITH THE BOLT SEAT WHEN THE LIMBS ARE IN ASSEMBLED ALIGNMENT, A PAIR OF GUIDE PIN SOCKETS TRANSFIXING SAID JOINT AND LOCATED IN THE OPPOSING SURFACES OF THE LIMBS IN SPACED RELATION FORE AND AFT THE MIDDLE OF THE JOINT, A PAIR OF GUIDE PINS ADAPTED TO SEAT IN SAID GUIDE PIN SOCKETS TO ALIGN THE LIMBS WHEN ASSEMBLED, AND A BOLT ADAPTED TO ENGAGE SAID BOLT SEAT AND BOLT SOCKET TO COMPRESSEDLY JOIN SAID LIMBS AND SAID PLATES WITH CONSEQUENT COMPRESSION OF THE FORE AND AFT OUTER PORTIONS OF THE LIMBS.