Abstract:
A double-ended hexagonal shank tool bit for extracting Phillips head or similar screws with damaged heads. One end of the tool shapes the screw head recess to a flared opening. The other end of the tool is tapered with left-hand screw threads and diametrically opposite longitudinal gashes arranged to enable the tool to engage the sides of the shaped recess and remove the screw.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims priority under my co-pending provisional patent application Serial No. 60/392,063, filed Jul. 1, 2002. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    This invention relates to a tool for extracting screws with damaged screw heads. More specifically, this invention relates to a single-piece tool adapted to be installed in the chuck of a counter-clockwise rotating drill to extract screws with damaged screw heads of the type with symmetrical recesses, such as Phillips or Robinson type screw heads.  
           [0003]    The prior art discloses a number of threaded devices for removing broken bolts or studs. For instance, U.S. Pat. No. 1,105,535, which issued Jul. 28, 1914 to J. O. Roberts, discloses merely a steeply pitched left-hand auger bit adapted to be inserted into a hole separately drilled in the broken bolt. The bit is turned counter-clockwise to remove the broken bolt.  
           [0004]    U.S. Pat. No. 2,062,383, which issued Dec. 1, 1936 to M. A. West discloses a double-ended tool having threads of opposite hand on its respective ends. The reaming and removing end has a beveled tip and the driving end has a flat tip. Both ends operate in the recess of a special screw.  
           [0005]    U.S. Pat. No. 2,281,164 which issued Apr. 28, 1942 to H. S. Maling discloses a right-hand threaded sleeve adapted to be screwed into the hole of the broken bolt; the sleeve having a left-hand threaded bore into which a threaded mandrel is screwed, the mandrel having teeth or nibs on its bottom to dig into the bolt remnant so that the remnant is removed as the sleeve is unscrewed.  
           [0006]    A screw extractor in the Berendzen 4,078,458 which issued Mar. 14, 1978 discloses a drill on the end of a tapered threaded cone whereby a hole can be drilled in the remnant and, drilling farther, the cone can engage the margins of the hole to spin the remnant out of its threaded hole.  
           [0007]    A number of extractor patents have issued to Eli Polonsky in which a left-hand drill bit is provided with a gripping fixture on its stem, and adapted to bite into the hole made by the drill so that the remnant may be removed in a single operation as the device is turned counter-clockwise. The Polonsky patents are 4,604,917, which issued Aug. 22, 1986; 4,777,850, which issued Oct. 28, 1928; and 5,032,487, which issued Jul. 16, 1991.  
           [0008]    U.S. Pat. No. 5,251,516 and U.S. Design Pat. D 340,184, both issued Oct. 12, 1993 in the name of Donald Desaulniers and assigned to Alden Corporation, disclose tools for extracting broken bolts and the like. One end of the tool drills a cylindrical hole in the remnant, and the other end has a gently tapered extraction section with a left-hand thread for biting into the side of the hole thus drilled to enable removing the remnant.  
           [0009]    Most of the previous extractor techniques involve first drilling a hole into a remnant in which the screw head is broken off or missing, and then inserting some form of extractor which engages the drilled hole thereby allowing the remnant to be rotated out of its bore. However in many cases, the screw head remains attached to the screw proper, but the screw head is damaged when attempting to remove the screw. This problem is particularly acute when a screw head has a symmetrical recess adapted to mate with a special tool, which damages the screw head while attempting to remove the screw, so that it can no longer obtain a purchase on the screw head. In such a case the tool will merely turn in the recess and slip from one position to the next without generating enough torque to remove the screw. Typical of this problem are Phillips head and Robinson head screws, which become damaged and are difficult or impossible to remove with the regular tools designed for this purpose.  
           [0010]    Accordingly, one object of the present invention is to provide an improved tool for removing screws or bolts with damaged screw heads.  
           [0011]    Another object of the invention is to provide an improved single-piece tool adapted to be installed in the chuck of a counter-clockwise rotating drill to extract screws with damaged screw heads of the type with symmetrical recesses, such as Phillips or Robinson type screw heads.  
         SUMMARY OF THE INVENTION  
         [0012]    Briefly stated, the invention comprises a tool for extracting screws with damaged screw heads of the type with a symmetrical center recess defining circumferentially spaced recess extensions having a major diameter, alternating with resistive sections having a minor diameter. The tool has a central section with flat longitudinal surfaces adapted to be engaged by a drill chuck, a left-hand recess-forming section at one end of the central section, the recess-forming section having a forming distal end with a first portion arranged to make a cylindrical drilled hole with a diameter intermediate the major and minor diameters into the resistive sections and a second flared portion curving away from the axis of rotation so as to form the resistive sections into a flared shape, which is designed to limit the depth of the cylindrical hole so that it does not extend from the screw head into the screw proper. A screw-removing section is provided at the other end of the central section, the screw-removing section having a tapered portion extending toward its distal end and being formed with left hand threads on the exterior of the tapered portion, the tapered portion being at an angle such that the tapered portion threads will engage the flared walls of the resistive sections as the tool is inserted into the recess. Preferably the tapered portion further includes at least one longitudinal gash extending along the tapered portion and interrupting the threads, so as to facilitate engagement of the threads to enhance the screw-removing process. In its preferred form, the tapered portion is frusto-conical with two diametrically opposed gashes skewed slightly with the axis of rotation. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    Other features and objects of the invention will be apparent to those skilled in the art after a study of the following specification, including reference to the appended drawings, all of which show a non-limiting embodiment of the invention. In the drawings:  
         [0014]    [0014]FIG. 1 is a front elevational view of the improved screw-extracting tool,  
         [0015]    [0015]FIGS. 2 a  and  2   b  are enlarged left end and front elevational views, respectively of the recess-forming section, on the left hand end of the tool of FIG. 1,  
         [0016]    [0016]FIGS. 3 a  and  3   b  are enlarged front and right end views, respectively, of the screw-removing section on the right hand end of the tool of FIG. 1,  
         [0017]    [0017]FIGS. 4 a  and  4   b  are enlarged fragmentary elevation section and top plan views, respectively, of a Phillips head screw with a damaged screw head,  
         [0018]    [0018]FIGS. 5 a  and  5   b  are enlarged fragmentary elevation section and top plan views, respectively, of the Phillips head screw of FIGS. 4 a  and  4   c  after use of the recess-forming section of the tool, and  
         [0019]    [0019]FIG. 6 is an enlarged fragmentary section showing engagement of the previous Phillips head screw by the screw removing section of the tool. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0020]    A tool embodying the invention is shown in FIG. 1 and generally designated  10 . It comprises a central section  12  having a plurality of flat longitudinal surfaces  14  adapted to be engaged by a drill chuck. The section  12  of the FIG. 1 embodiment is hexagonal in cross section.  
         [0021]    On the left hand end of the central section  12  shown in FIG. 1 there is provided a left-hand recess-forming section  16 . The tool is necked in at  18  between the central section  12  and the recess-forming section  16  in order to help locate the tool in certain types of standard chucks. The recess forming section  16  is made up of a cylindrical hole-drilling portion  20  and a flared portion  22  terminating in a short hexagonal portion  24 .  
         [0022]    On the right hand end of the central section  12  in FIG. 1 is a screw-removing section  26  with a tapered portion  28 , narrowing toward its distal end; that is, the end not connected to the central section  12 . The tapered resistive section is formed with left-hand threads  30  on the exterior of the taper as shown.  
         [0023]    The distal end of the threaded tapered portion is formed with a peripheral chamfer  32 . The proximal or larger end of the tapered portion terminates at  34 . The area between the central section  12  and the end  34  of the tapered portion is necked down at  36  to help locate the tool in the chuck.  
         [0024]    Referring now to FIGS. 2 a  and  2   b  of the drawings further details are shown for the recess-forming section  16 . The end elevation view of FIG. 2 a  is shown looking toward the chuck (not shown) of a rotary drill rotating in a left-hand or screw removing direction. A first drilling portion  20  is formed as a drill bit with a pair of oppositely directed cutting edges  38  and a pair of oppositely directed relief edges  40  arranged to drill a cylindrical hole when the drill is rotated in a left-hand direction. Continuing from the first portion drilling  20  is a second flaring portion  22  with oppositely directed curved cutting edges  42  and curved relief edges  44 . The cutting edges  42 ,  44  flare out until they intersect the hexagonal section and thereby serve to limit the depth to which the recess-forming section can drill the cylindrical hole, the depth of which is preferably only slightly greater than the depth of the screw head so as not to unduly weaken the juncture between the screw head and the screw proper. In order to accomplish this, the axial lengths of the recess-forming section  16  is pre-selected to only slightly exceed the depth of a pre-selected screw head, e.g., on the order of {fraction (1/16)} inch.  
         [0025]    Referring now to FIGS. 3 a  and  3   b  of the drawings, further details are shown for the screw-removing section  26 . The end elevation view of FIG. 3 b  is again shown looking toward the chuck (not shown) of a rotary drill rotating in a left-hand or screw removing direction, or clockwise in FIG. 3 b  as indicated by the arrows. The tapered portion  28 , shown in FIG. 3 a  is preferably frusto-conical as shown. The taper is at an angle A to the axis of rotation of the tool in a range of from 7° to 17° and is preferably about 12°. The threads  30  are left-hand threads, i.e., helically oriented on the tapered portion so as to screw into the workpiece when the drill is operated in a reverse or left hand direction. The preferred pitch of the threads is in a range of 20 to 28 threads per inch depending on the size screw. For example, I prefer to use 24 threads per inch for standard No. 2 or No. 3 Phillips head screws.  
         [0026]    In accordance with one aspect of the invention, two longitudinal gashes  46  are disposed diametrically opposite one another and interrupt the threads  30 . There should be at least one such gash and as many as four are useful to enhance the ability of the threads to obtain purchase on the flared walls of the resistive sections of the screw head, as will be explained in further detail.  
         [0027]    The gashes  46  are skewed slightly at an angle of about 4° with respect to the axis of rotation. The direction of the skew is such that a distal end  48  of the gash  46  engages first and a proximal end  49  of the gash engages last as the tool rotates. This is evident from the view shown in FIG. 3 b  of the drawing.  
         [0028]    [0028]FIGS. 5 a  and  5   b  show a standard Phillips head screw segment  50  with a screw head  52 , a gently tapered neck  54  and part of a threaded portion  56  imbedded in a substrate  58 . The screw head  52  defines a cruciform recess made up of circumferentially spaced slots  60  with outermost end extensions  62  located at a major diameter at the top of the recess and alternating with circumferentially spaced resistive sections  64  extending radially inward at the top of the recess to a minor diameter. The recess extensions  62  taper down into the screw head from the major diameter at the top of the screw head to the minor diameter at the bottom of the recess as shown in FIG. 4 a . Normally the resistive sections  64  conform to the minor diameter at the top of the screw head, so that the Phillips head screwdriver can obtain purchase on the screw. However, in this case, the screw head has been damaged by the screwdriver and worn off as shown at  66 , so that the screwdriver will no longer function properly.  
         [0029]    [0029]FIGS. 5 a  and  5   b  illustrate the same screw head  52  after the recess-forming section  16  of the tool (shown in dashed lines) has been inserted into the damaged screw head recess and rotated counter-clockwise. A cylindrical hole  70  has been drilled, which is of greater diameter than the minor diameter, and a flared portion  72  has been formed in the resistive sections  64  (FIG. 4 b ). Portions of the slotted extensions  62  are still present.  
         [0030]    The flared section  72  that is created by the recess-forming section  16  of the tool is precisely formed to cooperate with the screw-removing section  26  of the tool. The tool is removed from the chuck, turned end for end and rotated in a counter-clockwise direction at slow speed. FIG. 6 illustrates the section  26  of the tool, with the tapered portion  28  of the inserted into the screw head recess. The left-hand threads  30  gradually engage the flared walls  72  and bite into the walls lodging the tool firmly into the screw head  52 . The engagement action is facilitated by the skewed gashes  46  that provide surfaces on the interrupted threads  30  to enhance the engagement. Since the distal end of the gash engages before the proximal end as the tool rotates, the engagement surfaces of the threads  30  engage the resistive sections  64  of the screw head successively rather than simultaneously. This enhances the ability of the tapered portion  28  to lodge in the resistive section  64 . Continued slow rotation exerts counterclockwise torque to withdraw the screw. It should be understood that the tool of the invention is designed to work with a portable or a stationary drill, the condition being that the drill must be run in a counter-clockwise or left-hand direction.  
         [0031]    One of the reasons for the center section being hexagonal is that when the screw is removed and still attached to the screw-removing section, the screw may be clamped in a vice and a wrench or socket applied onto the axial central section. Turning the wrench section clockwise, the tool is removed from the damaged screw and ready for reuse. Also, in the removal process, if the drill stalls, the chuck can be opened and the drill disengaged and taken out of the way and a wrench may be used on the hexagonal shape of the central section to manually proceed with the extraction.  
         [0032]    The above description relates only to the preferred form of the invention. The invention is not limited to the embodiment described but is receptive to reasonable variations, The protection to which the invention is entitled, therefore, is limited only by the scope of the following claim language and such extension of the right to exclude others from making, using and selling as is appropriate under the doctrine of equivalents.