Patent Publication Number: US-3877826-A

Title: Handle connection for impact tools

Description:
United States Patent [191 Shepherd, Jr. et al.  
 [11] I 3,877,826 1 Apr. 15, 1975 HANDLE CONNECTION FOR IMPACT TOOLS [73] Assignee: The Stanley Works, New Britain,  
 Conn.  
 [22] Filed: Mar. 12, 1973 [21] Appl. No.1 340,259  
 [52] U.S. Cl 403/267; 145/29 R; 145/61 R [51] Int. Cl. B25g 3/34 [58] Field of Search..... 306/32, 33; 145/29 R, 29 B, [45/36, 61 R; 287/202 R; 151/14.5;  
 OTHER PUBLICATIONS The Plastics Manual, June 18, 1971, Published by Applied Plastics.  
 Encyclopedia of Polymer Science &amp; Technology, (Volume 10), Nov. 17, 1970.  
 Primary ExaminerWerner I-I. Schroeder Assistant Examiner-Conrad L. Berman Attorney, Agent, or Firm-Prutzman, Hayes, Kalb &amp; Chilton [5 7] ABSTRACT An impact tool such as a hammer is provided with a metallic tool head having a handle-receiving eye in which a portion of the eye spaced from the entrance end increases in cross section toward the exit end and is also provided with a non-metallic handle having an end portion within the eye dimensioned to form a tight fit with the entrance end of the eye but having a clearance between it and the portion of the eye which increases in cross section, said end portion in addition having a peripheral indentation or recess in its outer surface, and a tough, hard and rigid molded plastic, preferably glass-filled, in the space between the end portion of the handle and the eye interlocking with the handle and having wedging engagement with the portion of the eye of increasing cross section thus effectively locking the parts against looseness and separation.  
 9 Claims, 3 Drawing Figures HANDLE CONNECTION FOR IMPACT TOOLS BACKGROUND AND SUMMARY OF THE INVENTION The present invention relates in general to impact tools such as hammers, axes, hatchets and similar hand tools and is concerned more particularly with an improved connection between the tool head and handle for overcoming the tendency in such tools under normal conditions of usage to develop looseness between and separation of the head and handle. The invention is particularly advantageous for use in such tools where the handle is formed for non-metallic material such as wood or plastic.  
  Impact tools such as hammers have long been made with metallic heads and non-metallic handles, with the end of the handle inserted into and secured to a central opening or eye in the head. The principal and traditional way of forming the connection between the head and end of the handle has been to provide the eye of the head with an outward flare or enlarged cross section toward its exit end and to expand the end of the handle which has been inserted through the smaller entrance end of the eye into tight contact throughout with the eye by wedging. This is accomplished by driving one or more wedges into the exposed end of the hammer forcing the end of the handle to expand or enlarge and bringing its periphery into compressive contact with the eye. While such connections are initially very tight, it is well known that they tend to deteriorate rapidly during normal usage of the tool. The exceedingly large and intermittent stresses that occur during usage of the tool together with such other factors as the presence of fissures in the end of the handle produced by the wedges, and the alternate swelling and contraction of the handle end as a result of changing ambient humidity conditions, all contribute to rapid deterioration of the tight fit resulting in looseness and eventual separation.  
  With the advent of improved adhesives and particularly the thermoplastic resin adhesives such as epoxy resins, such materials have been used to bond the handle to the eye of the tool head without or in combination with wedging. However, it has been found that in order to produce an effective connection including damping of the vibrations of the tool head, it is necessary when employing this technique to provide direct contact between the handle and metallic head throughout a substantial portion of the eye thus greatly reducing the available area for adhesive bonding. This limitation together with the inherent limitations of the bonding material frequently results in rapid fracture or release of the adhesive bond under stress, thus permitting the handle to loosen and be released without material increase in service life. Attempts to use rubber and rubber-like fillers or packings have met with similar difficulties.  
  Accordingly, it is an object of the present invention to provide a handle connection for impact tools which avoids the above-mentioned disadvantages and which affords a tight effective connection between the head and handle having a long service life before repair or replacement is required.  
  Another object is to provide such a connection which can be made without difficulty using readily available materials and with consistent high quality whereby the use of the invention is economically attractive as well as producing improved results.  
  A further object is to provide such a handle connection which will not adversely affect the desired qualities of the tool such as balance and absorption of vibrations and will not deteriorate due to external or ambient conditions.  
  Other objects will be in part obvious and in part pointed out in more detail hereinafter.  
  These and related objects are accomplished in accordance with the present invention by providing the eye of the tool head and the end of the handle with cooperating contours including spaced apart opposed surfaces in a direction axially of the handle and preferably at least one inclined camming or wedging surface on the interior of the eye and a peripheral recess in its handle, and filling the space between the surfaces with a suitable moldable plastic which sets up as a tough, hard and rigid mechanical interlock preventing relative axial movement of the handle and head thus maintaining a tight and durable connection effective over long periods of service.  
  A better understanding of the invention will be obtained from the following detailed description and accompanying drawing illustrating various preferred embodiments in which the principle of the invention is employed.  
 BRIEF DESCRIPTION OF THE DRAWING In the drawing:  
  FIG. 1 is a fragmentary side view of a hammer, partially in cross section, showing a preferred embodiment of a handle connection formed in accordance with the invention;  
  FIG. 2 is a fragmentary end view with a portion in section taken generally along the line 22 of FIG. 1;  
  FIG. 3 is a top view thereof but with the plastic omitted.  
 DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawings, the invention is shown embodied in a hammer having a forged steel hammer head 10 of the claw type provided with the usual poll and bell II at one end and claws 12 at the other. Centrally of the head 10 is a handle receiving eye 13 which is a through opening having an entrance end 14 at the outer end of the boss 15 and an exit end 16 at the upper face of the head 10. In the specific embodiment, the cross section of the eye 13 is shown as generally rectangular although as will be apparent, the invention will apply equally to other cross-sectional configurations such as oval or round.  
  The entrance region 17 adjacent the entrance end 14, which in the specific embodiment extends slightly less than one-third of the length of the eye, is of uniform cross section throughout or with a very minor flare or divergence toward the entrance end 14. The function of the entrance region 17 is to form a tight frictional engagement with the end of the handle 18 when it is driven in from the entrance end 14, the handle end being dimensioned so that it will be slightly compressed at the entrance region and so that the entrance end 14 will dig slightly into the material of the handle when the handle end is fully inserted to form a tight seal.  
  The remaining region 19 of the eye 13 gradually increases in cross section toward the exit end 16. This is provided&#39;in part, by a slight forward inclination of the front end surface and a slight rearward inclination of the rear end surface 21. While the amount ofinclination may vary in the practice of the invention, it may be mentioned by way of example that in the specific embodiment shown in the drawings, the dimension of the eye 13 from front end surface to rear end surface at the exit end exceeds that at the entrance end by the order of approximately one-quarter to three-sixteenth of an inch. In the specific embodiment the transverse dimension of the eye 13 also increases toward the exit end in that the side surfaces 22 and 23 are formed with a very minor outward flare toward the exit end 16.  
  As thus far described, the hammer head 10 and its eye configuration is very similar to that of a conventional hammer head construction as used when a nonmetallic handle is to be secured thereto by conventional wedging with the advantage that fabrication may be carried out without need for substantially changing existing equipment and manufacturing techniques presently used in the fabrication of impact tool heads previously manufactured.  
  The end portion of the handle 18 which in the specific embodiment is a wooden handle, is received in the eye 13 by insertion through the entrance end of the eye. The end portion of the handle 18 inserted into the eye is modified in accordance with the invention to provide a head portion 24 of smaller cross section than the portion of the eye 13 adjacent the exit end 16 and having a clearance between it and the eye 13 around its entire periphery and throughout its length. In the preferred embodiment, the sides of head portion 24 taper inwardly slightly toward the exit end for optimum clearance. The shoulder portion 25, of the handle is dimensioned to provide a friction fit and to form a tight connection with the entrance region 17 of the eye 13. Adjacent the shoulder portion 25 and between it and the head portion 24 is a reduced section 26 which in its preferred embodiment is formed by a circumferential groove which is relatively wide but shallow and formed with beveled edges. A typical groove would be one having a width of the order of one-fourth inch and a depth of the order of one-eighth inch. When specific dimensions are given herein, they are intended as a specific example of a preferred embodiment but without limitation since the dimensions maybe varied within reasonable limits and necessarily will vary with the type and size of tool. In the preferred embodiment, the head por tion 24 is shown as terminating slightly short of the exit end 16 of the eye, but this is not essential and the end of the handle may be formedflush with the exit end 16 if preferred.  
  In accordance with the invention, the peripheral space around the end of the handle and between the handle and eye, and also the exit end of the eye 13 if the handle end does not extend for the full length of the eye, is filled with a tough, hard and rigid plastic 27 of the type having high impact resistance and dimensional stability. Among the known commercially available plastics having the necessary physical characteristics for this purpose, for example, are polycarbonates such as sold under the trademark Merlon by Mobay Chemical Company and the trademark Lexan by General Electric Company, acetals such as the acetal homopolymers sold under the trademark Oebrin by E. l. duPont de Nemours &amp; Company, Inc. and the acetal copolymers sold under the trademark Celcon by Celanese Corporation, and ABS resins (acrylonitrile, butadiene and styrene) as sold under the trademarks Kralastic,  
 Lustron, Cycolac and Abson by Uniroyal Chemical. 7 Borg- Company, Monsanto Chemical Company, Warner Corp, and Goodrich-Gulf Chemicals, Inc., respectively. Also, these resins may have fibrous glass incorporated in them, usually in the range of 10 to 20 percent, which enhances stiffness, creep resistance and dimensional stability, and the use of such glass-filled.  
 resins such as a 20 percent glass reinforced ABS plastic, for example, is preferred. These plastics are generally classified in the trade as rigid molding materials and may have characteristics which in some respects such as creep resistance approach that of some nonferi tively high hS-fil distortion temperature, and minimum mold shrinkage.  
 Since the noldable resins which may be utilized in accordance with the invention are, or may be rendered, flowable prior to setting, it is possible and preferable to fill the cavity between the handle end and eye by injecting the flowable plastic from the exit end 16 under high pressure using conventional injection molding equip ment. The substantial spacing between the head portion 24 of the handle and the eye facilitates the injec-.&#39;  
 tion of the plastic and insures that the plastic, will readily flow into this space and the groove 26 and will set up as a continuous and unitary mass completely filling all of the cavities. As the shoulder portion 25 of the handle forms a tight fit with the entrance region 17 of the eye, this provides a seal which readily withstands the high pressure of the molten plastic during the injection cycle.  
  As will be apparent, the plastic mass 27 when solidified provides a unitary tough, hard and rigid connecting element forming a mechanical lock between the handle and the eye of the head. The plastic mass in final molded form has an integral bead 28 which mechanically interlocks with the groove 26 and its upper portion increases in thickness and cross-section toward the exit end of the eye to form a wedge complementary to the wedging surfaces of the eye. The result is an interference fit engaging in shear with the reduced section 26 of the end of the handle 18 and a wedging fit with the outwardly tapering surfaces of the eye 13 which cannot separate or loosen short of the destruction of the respective materials. Also, the tapered surfaces of the eye can be viewed as at least partially opposed to the upper edge of the groove 26 which are blocked apart by the hard plastic mass 27.  
  Although the plastics specifically mentioned above as usable in the invention are primarily regarded as molding compositions which do not have adhesive characteristics, this lack of adhesive qualities is of no adverse consequence in the practice of the invention because the interconnection formed is mechanical in function and not dependent on adhesiveness. It will also. be  
 noted that in the preferred embodiment, the plastic 27 is in contact with a large surface area of both the eye and handle end, and particularly the major portion located above the shoulder 25, it being an advantage of the present invention attributable in part to the physical characteristics of the resin used that it is unnecessary to have an extended surface-to-surface contact between the wood handle and metal eye as has usually been deemed necessary when forming the handle connections of the prior art.  
  Handle connections made in accordance with the present invention have exhibited a marked improvement with respect to durability and particularly with respect to resisting the onset of looseness and eventual separation of the head and handle. For example, a standard test which is significant in measuring the durability of a handle connection is to apply a transverse force to the handle relative to the head to simulate a nailpulling operation. In this test, with the head clamped in a stationary position and a force of 1,500 pound inches repeatedly applied to the end of the handle in a direction away from the claws, ordinary hammers in which the wooden handles were secured by conventional wedging techniques, develope a looseness of the order of 0.054 inches measured three inches from the eye after only 150 cycles. Samples of wooden-handled hammers made in accordance with the present invention on the other hand when tested in this manner remained intact and developed no appreciable looseness after 12,000 cycles at which point the tests were discontinued.  
  Another standard test which has been found to be significant in measuring the durability of a handle connection is to place the hammer in a testing machine which produces successive blows of the hammer against a steel anvil at a velocity of approximately 26 ft./sec. which is roughly equivalent to a normal full arm swing. Ordinary hammers in which the wooden handle is secured to the head by conventional wedging when tested on such a machine and subjected to 6,000 blows, develop a looseness of the order of 0.064 inches measured three inches from the eye. As compared therewith, representative samples of hammers fabricated and assembled in accordance with the present invention which have been subjected to this test and subjected to 6,000 blows on the machine, have remained tight without development of any appreciable looseness.  
  When subjected to humidity tests, conventional wood handled hammers after 7 days at specific humidity of 720 at 130F followed by 7 days at specific humidity of 40 at 72F developed a looseness of the order of 0.074 inches measured 3 inches from the eye, while hammers made in accordance with the preferred embodiment after being subjected to the same conditions developed no appreciable looseness.  
  It will be noted that in addition to providing a handle connection which maintains a tight connection between the handle and head under the high stresses to which the hammer is subjected during normal usage, and which is highly resistant to humidity, the plastic used has a wide range of service temperatures and has good chemical resistance and weatherability which ensures that the connection will not deteriorate due to environmental or ambient conditions, particularly when the plastic also covers over the end of the handle at the exit end of the eye as shown in the preferred embodiment.  
  As will be apparent to persons skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the teachings of the present invention.  
 We claim:  
  1. An impact tool comprising a metallic head with a handle receiving eye therein having an entrance end and an exit end, said eye having a portion which progressively increases in cross-section toward the exit end, a handle having an end portion within the eye, said end portion having a shoulder portion forming a tight connection with the head over an area at the entrance end of the eye, a recessed circumferential groove adjacent said shoulder portion and spaced from the entrance end of the eye, and a wedge-free head portion spaced from the shoulder portion having a larger crosssection than the recessed portion but a smaller crosssection than the progressively increasing cross-section of the eye to provide a clearance therebetween which extends entirely around the periphery of said head portion and which progressively increases in cross-section toward the exit end of the eye, and a tough, hard and rigid injection molded thermoplastic material in the space within the eye between the end portion of the handle and the head, said thermoplastic material tightly engaging said wedge-free head portion and said recessed portion while&#39;intimately contacting the progressively increasing eye portion to encapsulate said head portion and form a mechanical lock between the handle and the head.  
  2. The impact tool of claim 1 wherein the portion of said eye of enlarged cross-section is formed with side walls which taper upwardly and outwardly toward the exit end of the eye, whereby the molded plastic material mechanically interlocks with the groove and has a wedging fit with the eye.  
  3. The impact tool of claim 1 wherein the molded plastic material comprises a resin of the type having a tensile strength of the order of 9,000 psi and a minimum compressive strength of the order of 12,000 psi.  
  4. The impact tool of claim 1 wherein the molded plastic material is a thermoplastic resin selected from the group consisting of polycarbonate, acetal and ABS resins, and glass fiber reinforced resins of said group.  
  5. The impact tool of claim 1 wherein said groove is a relatively wide circumferential groove and the molded plastic material is a thermoplastic resin selected from the group consisting of polycarbonate, acetal and ABS resins, and glass fiber reinforced resins of said group.  
  6. The impact tool of claim 1 wherein the enlarged cross-section portion of the eye is formed with front and rear surfaces which are inclined upwardly and outwardly toward the exit end of the eye and wherein the clearance between the head portion of the handle and the eye extends around the entire circumference of the head portion, and wherein the molded plastic forms a hard and rigid unitary mass mechanically engaging with the recessed portion of the handle and having a wedging fit with the front and rear surfaces of the enlarged cross-section portion of the eye.  
  7. The impact tool of claim 6 wherein the molded plastic material is a thermoplastic resin selected from the group consisting of polycarbonate, acetal and ABS resins, and glass fiber reinforced resins of said group.  
  8. The impact tool of claim 5 wherein the end portion of the handle terminates short of the exit end of the eye and the molded plastic covers the end of the handle and closes the exit end of the eye.  
  9. The impact tool of claim 8 wherein the molded plastic material is a thermoplastic resin selected from the group consisting of polycarbonate, acetal and ABS resins, and glass fiber reinforced resins of said group. l