Abstract:
A tool handle assembly and method of electrically insulating a metal tool from a metal handle end piece to which the tool attaches includes an electrically insulating insert providing a gasket-like seal between an extension of the tool which extends through a handle grip and the handle end piece. In another aspect of the invention, a portion of the handle grip surrounds an internal air gap to provide shock absorption which protects the integrity of the water-tight seal between the exterior and interior of the handle assembly.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to tool handle assemblies, and more particularly relates to a tool handle assembly having a handle end piece which is electrically insulated from a metal tool to which the handle assembly attaches. 
         [0002]    Many tool handle assemblies have a handle end piece which is used to secure the tool to a handle. The handle, which is shaped for manually grasping and working of the tool, includes a longitudinal opening through which a separate part or extension of the tool extends at one end of the handle. The end piece mounts to the opposite end of the handle and attaches to the tool extension in the handle thereby securing the tool to the handle. In some designs, the tool and end piece are made of metal while the handle is made of an electrically insulating material such as plastic or rubber. Should the tool come into contact with electricity, electric current can travel through the tool extension inside the handle and reach the butt cap thereby shocking the hand of the user. 
         [0003]    Attempts to insulate a metal handle end piece from the metal tool have not been entirely successful in that the insulating barriers may fail should the handle assembly become wet. Should water leak past the insulating barrier, an electric circuit is completed between the tool and end piece and the user may receive a shock. Furthermore, many prior art handle assemblies (and thus also the insulating barrier) fail under the cumulative impact stresses which occur through normal use of the tool. 
       SUMMARY OF THE INVENTION 
       [0004]    In a first aspect, the present invention provides a handle assembly for a metal tool having a metal end piece which is electrically insulated from the tool. The tool may be a knife blade, for example. In one embodiment, an electrically insulating insert is positioned between the metal end piece and a metal extension of the tool extending within an opening in the handle. The engaging surfaces of the insert and end piece firmly secure these two parts together. The tool extension includes a coupling element which attaches to a bore formed in the insert thereby securing the end piece, insert and tool to the handle. 
         [0005]    In a second aspect of the invention, a portion of the handle opening is of a larger diameter and thereby radially spaced from the tool extension axially extending through the handle opening. The spacing between the handle and tool extension defines an air gap internally of the handle. The portion of the handle adjacent the air gap is made of a material which can absorb the shock (by flexing, for example) of a force applied to the tool or handle end piece. 
         [0006]    In one embodiment of the invention, the tool is a knife blade of the type used by soldiers where cutting through electrified wires is sometimes necessary. In another embodiment of the invention, the end piece may be a butt cap and the but cap may include a pointed end used for breaking glass, for example. In another embodiment, the end piece is a bayonet clip for mounting the knife to a firearm. 
     
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0007]      FIG. 1  is a perspective view of an embodiment of the invention with the tool shown fragmented; 
           [0008]      FIG. 2  is a perspective view of the embodiment of  FIG. 1  showing the end piece partly removed from the handle portion; 
           [0009]      FIG. 3  is an enlarged, perspective view of the embodiment of the invention of  FIGS. 1 and 2  and showing the end piece completely removed from the handle portion; 
           [0010]      FIG. 4  is a cross-sectional view as taken generally along the line  4 - 4  in  FIG. 1 ; and 
           [0011]      FIG. 5  is the view of  FIG. 1  showing an embodiment wherein the end piece is a bayonet latch. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    While the invention will be described with reference to a particular embodiment of the invention, it is understood that many modifications may be made thereto without departing from the full scope of the invention. Some particular modifications will be discussed herein while other modifications will be readily apparent to those skilled in the art. 
         [0013]    Referring now to the drawing, there is seen in the various figures an embodiment of the invention in the form of a knife  10  having a blade  12  and a handle assembly  14 . Blade  12  may be substituted with other types of tools as desired such as a hammer, screwdriver, file, or awl, for example. The tool or blade  12  is made of a strong metal material which by its nature is electrically conductive. An extension  16  connects to the blade  12  either as a separate or integral part thereof and is also made of a strong metal material which is electrically conductive. 
         [0014]    The handle assembly  14  includes a handle grip  18  made of an electrically insulating material such as plastic or rubber, for example. The handle assembly  14  further includes an end piece for securing the handle grip  18  to the knife blade  12  via extension  16 . The end piece may take a variety of forms and is preferably formed of a strong metal material which is inherently electrically conductive. In the embodiment of  FIGS. 1 ,  2  and  4 , the end piece is in the form of a butt cap  20 . But cap  20  may include a pointed end  20   a  which can be used for breaking glass, for example. This embodiment of knife  10  is particularly suited for pilots that may need to break through a downed aircraft windshield, for example. In the embodiment of  FIG. 5 , the end piece is in the form of a bayonet latch  23  for attaching knife  10  to a firearm (not shown). 
         [0015]    As seen best in  FIGS. 2 and 4 , handle grip  18  includes an opening  22  extending substantially axially along and entirely through the handle grip from the front end  18   a  to rear end  18   b  thereof. During assembly of the knife  10 , blade extension  16  is inserted into opening  22  at handle grip front end  18   a . Extension  16  includes an end piece coupling element at the end thereof opposite blade  12 . In the embodiment shown in the drawing, the end piece coupling element is in the form of a threaded shank  24  which may be separately attached or integrally formed with extension  16 . 
         [0016]    Handle assembly  14  further includes an insert  26  made of an electrically insulating material such as plastic or rubber, for example. As seen best in  FIG. 4 , insert  26  forms a gasket-like seal between butt cap  20 , handle grip  18 , and coupling element  24 . As such, insert  26  provides electric insulation between blade  12  and butt cap  20 . Although the overall configuration of insert  26  may vary according to the design of the end piece and coupling element, in the embodiment of  FIG. 4 , insert  26  includes a central portion  26   a  terminating in a head  26   b  which is cooperatively formed to fit snugly within a central bore  20   b  formed in butt cap  20 . The insert  26  also includes a central bore  26   c  formed through central portion  26   a . Butt cap  20  and insert  26  are attached together by inserting central portion  26   a  into central bore  20   b  of butt cap  20 . The insert central bore  26   c  is thus substantially axially aligned with butt cap central bore  20   b . Insert central bore  26   c  may include threads  26   d  to engage the threaded shank  24  of extension  16  and in this way secure butt cap  20  to handle grip  18 . 
         [0017]    Insert  26  further includes a flange  26   e  which extends radially outwardly of central portion  26   a . To provide a complete and uninterrupted electrically insulating barrier between butt cap  20  and blade  12  including extension  16  and coupling element  24 , insert flange  26   e  follows the contour of and lies in complete covering relation to the surfaces of butt cap  20  which would contact handle grip  18  and extension  16 . Referring still to  FIG. 4 , butt cap  20  is seen to include an annular neck portion  20   c  surrounded by an annular shoulder portion  20   d . To follow this contour, insert flange  26   c  integrally extends from central portion  26   a  with an inner shoulder segment  26   e  which leads into a neck segment  26   f  which leads into an outer shoulder segment  26   g.    
         [0018]    As stated above, it is important that handle assembly  14  be water-tight since water entering the handle assembly could create an electric path that bypasses insert  26  causing a shock to the user at butt cap  20  should blade  12  come into contact with a source of electricity. In this regard, the insert-butt cap interface geometry is provided with a plurality of discontinuous, interfacing surfaces to create a tortuous path between the exterior and interior of handle assembly  14 . For example, to create this geometry, insert annular neck portion  20   c  may include a squared notch  20   e  which interfaces with a squared flange  26   h  of insert  26 . This squared notch-flange interface alone has three discontinuous, interfacing surfaces. Another benefit of this squared notch-flange interface is that it provides a very secure fit between insert  26  and butt cap  20 . A second squared notch-flange interface  27  may be provided adjacent head portion  26   b , for example, for added bond strength between these parts. Other insert-butt cap interface geometries are of course possible. 
         [0019]    In one embodiment, the insert  26  is molded into butt cap  20  which, combined with the notch-flange interfaces, creates an extremely secure bond between these two parts. During assembly, butt cap  20  is screwed onto threaded shank  24  and a sealant may be provided at the interfacing surfaces of insert  26  and handle grip  18   a  to further ensure a watertight seal between the exterior and interior of handle assembly  14 . 
         [0020]    A portion  18   a  of handle grip  18  is radially spaced from coupling element  24  (or extension  16  in an embodiment where the coupling element does not extend outwardly of the insert central bore  26   c ) to form an air gap  28  therebetween. Insert shoulder segment  26   e  radially spans air gap  28  such that air gap  28  is an enclosed space, being defined by shoulder segment  26   e , handle grip portion  18   a , extension  16  and coupling element  24 . The handle grip portion  18   a  is made of a material which can absorb the shock (by flexing, for example) of a force applied to any part of knife  10  including the extreme impact force received when using butt cap pointed end  20   a  to break through glass, for example. With air gap  28  and handle grip portion  18   a  absorbing these shocks, the integrity of the handle assembly and seal between insert  26 , handle grip  16  and butt cap  20  is protected through the expected rigorous use of knife  10 . 
         [0021]    While the invention has been described with reference to particular embodiments thereof, it is understood that various modifications may be made thereto without departing from the full spirit and scope of the invention as defined by the claims which follow.