Abstract:
A utility knife is provided with a guard for preventing the user&#39;s fingers from being lacerated by the blade or from being abraded by contact with material being cut. The guard can be a removable guard attachable to the knife using a fastener that also secures two halves of the knife handle together. The removable guard can include a work-engaging member with a slot through which the blade protrudes. The cutting depth, or the angle of the work-engaging member can be adjusted by providing in the guard a suitable slot through which the fastener extends. Different kinds of work-engaging members can be provided, including an insulation stripping guide, a guide having narrow ends aligned with the blade for visual guidance, and a guide having diverging sides for cutting flooring.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to utility knives, and more particularly to a utility knife having capabilities advantageous to roofers, builders, electricians, flooring installers, and other individuals who make extensive use of such knives. 
       BACKGROUND OF THE INVENTION 
       [0002]    A conventional utility knife comprises an elongated handle shaped to fit comfortably in an individual&#39;s hand, and a blade fixed to, and extending from one end of, the handle. A typical utility knife blade has a trapezoidal shape, with its cutting edge extending along the longer base of the trapezoid. The blade is usually replaceable, and when installed in the handle, extends therefrom in such a way that the shorter base of the trapezoid is fully or almost fully enclosed within the handle. Consequently, the exposed part of the blade is generally in the form of a trapezoid or a triangle. 
         [0003]    Ordinarily, the handle consists of two similar parts that meet each other in a plane along which the blade extends. 
         [0004]    The parts are held together by one or more machine screws. One or more protrusions within one of the handle parts cooperate with notches in the shorter base of the trapezoidal blade to secure the blade against longitudinal movement relative to the handle when the handle parts are fitted together. The handle is also usually hollow, and the space inside the handle can be used to store spare blades. 
         [0005]    The conventional utility knife handle has a tapered transition from the part that is grasped to the end from which the blade extends. A roofer who works with asphalt shingles typically makes extensive use of a utility knife to cut shingles, roofing paper, rubber waterproofing sheets, and other sheet roofing material. Slipping of the hand along the knife handle in the direction of the blade due to fatigue, moisture, inattention and other factors can result in laceration by the cutting edge of the blade or abrasion by contact with the hard granules embedded in an asphalt shingle. Other workers who use utility knives are subject to similar injuries. 
         [0006]    Roofers, and other workers who use utility knives, frequently have occasion to cut a surface only to a limited depth, shorter than the distance by which the cutting edge of a typical utility knife blade protrudes from the knife handle. For example, gypsum roofing board used for fire protection, such as “DENSDECK DURAGUARD” roofing board, is cut to size by scoring along a straight line and then snapping the parts on both sides of the score line apart. To score such materials properly with a utility knife, the cutting depth of the knife blade should be relatively small, and in any event less than the thickness of the material. 
         [0007]    Although some utility knives having retractable blades can be adjusted to set the cutting depth, a conventional knife in which the trapezoidal blade is secured against longitudinal movement by the engagement of protrusions within the handle with notches along its short base has no capability of rapid cutting depth adjustment. The handle parts must be separated. Then, after the blade-holding protrusion or protrusions are engaged with other notches in the blade, the handle parts must be reassembled. The knife is limited to a relatively small number of discrete cutting depths, corresponding to a whole number equal to or less than the number of notches in the short base of the trapezoidal knife blade. 
         [0008]    It is also important, especially in roofing applications, to be able to cut shingles from the top by gripping a utility knife in such a way that the cutting edge faces in a direction away from the wrist, and also to cut other roofing materials such as rubber sheets from the underside by a pulling action in which the knife is gripped in such a way that the cutting edge faces in a direction toward the wrist. In the first of these instances, the knife handle is held in an oblique relationship to the work. In the second, the knife handle is generally perpendicular to the work. There is a risk of injury when operating a conventional utility knife in each of these two modes. 
       SUMMARY OF THE INVENTION 
       [0009]    This invention has potential to reduce the incidence of laceration, abrasion and similar injuries commonly sustained in the use of utility knives. Some embodiments of the invention can also provide for rapid adjustment of the length of the exposed cutting edge. In addition, some embodiments of the invention can provide for protection of the user in both of the above-mentioned oblique and perpendicular cutting modes, while providing for proper blade guidance and control of cutting depth in each mode. 
         [0010]    The utility knife in accordance with a first aspect of the invention comprises an elongated handle having opposite sides extending along the direction of elongation, and opposite ends spaced from each other along the direction of elongation. A blade is fixed to, and protrudes from, the handle at one of the opposite ends of the handle. The handle is provided with a guard comprising a pair of laterally protruding guard members positioned adjacent the end of the handle from which the blade protrudes. The guard members protrude respectively from the opposite sides of the handle by a distance sufficient to prevent a user&#39;s hand from sliding past the end of the handle from which the blade protrudes. 
         [0011]    In certain preferred embodiments of the invention, the guard is detachably connected to the handle and comprising a pair of side members spaced from each other and respectively in abutting relationship with opposite sides of the handle. The side members are rigidly connected to each other by a work-engaging member having a slot through which the blade extends. A fastener extends through a through hole in at least one of the side members and connects that side member to the handle. Where the handle comprises two separable elongated parts, the handle parts can be held together by the same fastener that connects the side member of the guard to the handle. 
         [0012]    The through hole can be an elongated through hole extending in a direction parallel to the blade, whereby, by loosening the fastener, the position of the work-engaging member relative to the handle can be adjusted. If the elongated through hole extends substantially parallel to the direction of elongation of the handle, by loosening the fastener, the position of the guard can be adjusted longitudinally for adjustment of the extent to which the blade is exposed beyond the work-engaging member. On the other hand, if the through hole extends in a direction transverse to the direction of elongation of the handle, by loosening the fastener, the angular relationship of the work-engaging member and the direction of elongation of the handle can be adjusted. 
         [0013]    In still another embodiment, at least two through holes are provided in one of the side members. The through holes are spaced from one another, and the fastener can be alternatively extended through one or another of the through holes for adjustment of the position of the work-engaging member relative to the handle. 
         [0014]    In still another embodiment, the work-engaging member is formed with two narrow ends, both aligned with the blade, and in which the blade extends through the slot in the work-engaging member between those narrow ends. In this embodiment, the narrow ends provide for improved visual guidance, enabling the user to follow a guide line drawn on a workpiece more accurately. 
         [0015]    In a modified embodiment, The work-engaging member is a concave U-shaped member adapted to receive an insulated cable. In still another modified embodiment, the work-engaging member can be a convex member having work-engaging surfaces on both sides of the slot, the work engaging surfaces both diverging from each other and being disposed at an angle of 135 degrees relative to the protruding part of the blade. 
         [0016]    In still another embodiment, the utility knife can have a detachable guard member with or without a work-engaging part, but with laterally protruding parts that prevent a user&#39;s hand from sliding past the end of the handle from which the blade protrudes. In this case, the utility knife comprises an elongated handle having opposite sides extending along the direction of elongation, and opposite ends spaced from each other along the direction of elongation. A blade is fixed to, and protrudes from, the handle at one of the opposite ends of the handle. A guard detachably connected to the handle, comprises a pair of side members which are spaced from each other and respectively in abutting relationship with opposite sides of the handle, the side members are rigidly connected to each other and each side member has a laterally protruding guard positioned adjacent the end of the handle from which the blade protrudes by a distance sufficient to prevent a user&#39;s hand from sliding past the end of the handle from which the blade protrudes. At least one of the side members has a through hole. A fastener extends through the through hole and connects the side member to the handle. 
         [0017]    Further embodiments, and other details and advantages of the invention will be apparent from the following description when read in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a side elevational view of a utility knife according to a first embodiment of the invention; 
           [0019]      FIG. 2  is an oblique perspective view of the utility knife of  FIG. 1 ; 
           [0020]      FIG. 3  is an oblique perspective view of a longitudinally adjustable guard in accordance with a second embodiment of the invention; 
           [0021]      FIG. 4  is an oblique perspective view of a utility knife equipped with the adjustable guard of  FIG. 3 ; 
           [0022]      FIG. 5  is an oblique perspective view of an angularly adjustable combination guard and guide for a utility knife, in accordance with a third embodiment of the invention; 
           [0023]      FIGS. 6 and 7  are oblique perspective views of a utility knife equipped with a combination guard and guide as shown in  FIG. 5 , respectively showing the combination guard and guide in two different angular positions; 
           [0024]      FIG. 8  is an oblique perspective view of a linearly adjustable combination guard and guide for a utility knife in accordance with a fourth embodiment of the invention; 
           [0025]      FIGS. 9 and 10  are oblique perspective views of a utility knife equipped with a combination guard and guide as shown in  FIG. 8 , respectively showing the combination guard and guide in two different linear positions relative to the body of the utility knife; 
           [0026]      FIG. 11  is an oblique perspective view of a linearly adjustable guide, in accordance with a fifth embodiment of the invention, for use with a utility knife in order to strip insulation from an electrical cable or the like; 
           [0027]      FIGS. 12 and 13  are oblique perspective view of a utility knife equipped with a guide as shown in  FIG. 11 , respectively showing the guide in two different linear positions relative to the body of the utility knife; 
           [0028]      FIG. 14  is an oblique perspective view of a modification of the utility knife of  FIGS. 1 and 2 , in which the guard is configured for use in cutting flexible flooring material such as linoleum or PVC sheets; 
           [0029]      FIG. 15  is a front elevational view of the utility knife of  FIG. 14 ; 
           [0030]      FIG. 16  is a partial side elevational view of the knife of  FIGS. 14 and 15 ; 
           [0031]      FIG. 17  is a bottom plan view of the guard on the knife of  FIGS. 14-16 ; and 
           [0032]      FIG. 18  is an oblique perspective view of a utility knife equipped with a linearly adjustable combination guard and guide configured for use in cutting flexible flooring material; 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0033]    The knife  20  shown in  FIGS. 1 and 2  is in most respects similar to a conventional utility knife, the knife handle being composed of two similar parts  22  and  24 , which meet each other in a plane  26  with respect to which the two handle parts are substantially symmetrical. Parts  22  and  24  are secured together by a machine screw  28 , which can be readily removed by means of a screwdriver, allowing the two parts to be separated from each other. 
         [0034]    When held together by screw  28 , handle parts  22  and  24  clamp a trapezoidal blade  30  in such a way that a part of the blade is exposed, protruding from a distal end  32  of the handle while the remainder of the blade is hidden inside the handle between the handle parts. As explained previously a conventional utility knife handle is typically hollow so that a space is provided for storage of spare blades, and one or both of the handle parts includes protrusions that fit into notches formed in an edge of the blade opposite form the cutting edge to secure the blade against longitudinal movement relative to the handle when the blade is clamped between the handle parts. The knife of  FIGS. 1 and 2  can be, and preferably is, constructed similarly. 
         [0035]    The handle parts of a conventional utility knife are typically cast from steel, aluminum or another suitable metal or metal alloy, or molded from a suitable polymeric resin. The knife if  FIGS. 1 and 2  differs from the conventional utility knife primarily in that protrusions are integrally formed with the handle parts  22  and  24 , and together form a guard  34 . Thus, a protrusion  36  is cast or molded as a unitary part of handle part  22 , and protrusion  38  is cast or molded as a unitary part of handle part  24 . 
         [0036]    Each of the protrusions  36  and  38  is preferably generally crescent-shaped, with a rounded outer edge as seen in  FIG. 2 . The proximal surfaces  40  and  42  of the protrusions  36  and  38  are engageable by the user&#39;s hands, and prevent the hands from contacting the blade and the work, i.e., the material being cut. Although the distal end  32  of the handle is preferably oblique relative to the direction of the long dimension of the handle, the proximal surfaces  40  and  42  of the guard protrusions are preferably more nearly perpendicular to the direction of the long dimension of the handle, so that they not only prevents the thumb and forefinger of the user from sliding in the distal direction on the handle, but can also comfortably engage the little finger and the adjacent metacarpal region of the hand when the handle is held in a “stabbing” configuration. 
         [0037]    Although, the proximal surfaces  40  and  42  can be flat, optionally, they can be formed with a slight concavity in order to fit the thumb and forefinger of the user. 
         [0038]    The benefits of the guard of the first embodiment can be realized by attachment of a retrofit guard unit to a conventional utility knife. Guard unit  44 , shown in  FIGS. 3 and 4 , is an example of a retrofit guard unit. The guard unit  44  is formed with a tubular wall  46 , and has an end opening  48  through which a conventional utility knife can be inserted into an interior space  50  shaped to conform to the distal portion of the knife. The guard unit is tapered at tapered portion  52 , and the end  54  opposite from opening  48  is provided with a slot through which a blade of the utility knife can protrude. Guard protrusions  56  and  58  are provided on opposite sides of the tapered portion  52  of the guard unit. These guard protrusions can be configured so that their upper surfaces are inclined forward and away from the part of end  54  through which the cutting edge of the blade extends. In a number of applications of a utility knife, it is important for the cutting edge of the knife blade to exert a large force on the material being cut. If the guard protrusions  56  and  58  are configured, as shown, so that they extend along the sides of the guard unit at an small angle relative to the cutting edge of the blade, the user, by pressing a thumb and fingers against the surfaces of the guard protrusions, can exert a large force in a direction perpendicular to the cutting edge of the blade. 
         [0039]    The wall  46  of the retrofit guard unit  44  is provided with a slot  60 , elongated in the direction in which the knife  62  ( FIG. 4 ) moves into space  50 . The slot has enlarged circular openings  64  and  66  at its opposite ends. The screw  68 , which holds the two halves of the knife handle together, extends through slot  60 , and its head fits in enlarge circular opening  64  at the distal end of slot  60  securing the guard unit, in a position providing for a predetermined degree of protrusion of the blade  70  beyond the end  54  of the guard unit  44 . The screw  68  is preferably a pan head or button head screw, having a circular, cylindrical outer surface that snugly fits either of the circular openings at the opposite ends of slot  60 , thereby preventing longitudinal movement of the guard unit relative to the knife handle but at the same time allowing the two halves of the knife handle to be securely fastened together by tightening of the screw. Since the screw used in a conventional utility knife is typically a countersunk, flat-head screw, a replacement screw having a pan head or a button head may be used to replace the conventional flat-head screw. In the embodiment shown, the retrofit guard unit can be positioned as shown in  FIG. 4 , with the screw head in circular opening  64 , or alternatively, with the screw head in circular opening  66 . In the former case, the knife blade  70  extends beyond the end  54  of the guard to a maximum extent. In the latter case, only a small portion of the knife blade  70  extends beyond the end  54  of the guard. The latter position can be used in scoring material, and in other applications where a limited cutting depth is required. 
         [0040]    In an alternative embodiment, not shown, the slot  60  can have one or more circular enlarged openings at intermediate positions between its end openings  64  and  66  to allow for additional discrete settings of the cutting depth. 
         [0041]    In still another alternative, the slot can be formed as a simple elongated slot without circular enlargements. In this case the screw head, the diameter of which should be larger than the slot width, can be tightened against the outer surface of the guard wall on both sides of the slot and hold the two halves of the knife handle together while at the same time securing the guard in a desired position. In this case, the cutting depth is not limited to discrete depths, but is continuously adjustable though a range determined by the length of the slot. 
         [0042]    As mentioned previously, a utility knife is most often held in such a way that the cutting edge faces in a direction away from the wrist. However, there are also occasions, for example the cutting of rubber sheets from the underside by a pulling action in which the knife is gripped so that the cutting edge faces toward the user&#39;s wrist. In the first of these instances, the knife handle is held in an oblique relationship to the work. In the second, where the knife handle is gripped in an entirely different manner, it is preferable to hold the knife handle generally perpendicular to the work. The embodiment depicted in  FIGS. 5-7  satisfies these objectives by means of an angularly adjustable guard unit  68 , which can be attached to a conventional utility knife  70 . 
         [0043]    As shown in  FIG. 5 , the guard unit comprises a U-shaped sleeve  72 , having an opening  74  between parallel side parts  76  and  78 . The width of the space between parts  76  and  78  corresponds to the width of the distal portion of the body of utility knife  70 , so that the distal portion can be received between parts  76  and  78  as shown in  FIGS. 6 and 7 . 
         [0044]    A plate  80  is provided at one end of the U-shaped sleeve  72 , the plate being welded, or otherwise suitably attached, to sleeve  72 . The plate  80  has a slot  82  through which the knife blade  84  can extend, and is shaped so with a double taper so that guide points  86  and  88  are formed at both ends of the plate along an imaginary line aligned with the slot  82 . Thus the guard unit can function as a combination guard and guide, preventing the user&#39;s hand from contacting the blade and the work, and also enables the user to follow a chalk line or other guide line drawn on the work. 
         [0045]    An arcuate slot  90  is formed in part  76  of the U-shaped sleeve  72  at a location such that a screw that holds the two parts of the knife handle together can extend through the slot when the knife blade extends through the slot  82 . The slot extends in a direction transverse to the direction of elongation of the knife handle. As shown in  FIG. 6 , the guard unit can be pivoted to a position in which the knife handle extends at an angle relative to the cutting edge  92  of the blade so that the work-engaging surface of the plate  80  is engaged in parallel relationship with the surface of the work while the handle is in an oblique relationship to the surface of the work. The guide is secured to the knife handle in the relationship shown in  FIG. 6  by tightening the head of screw  94  against the outer surface of part  76  of the sleeve, and the knife can be used in the conventional fashion. The screw can, of course, be tightened at any desired intermediate position in slot  90 . 
         [0046]    In the alternative configuration shown in  FIG. 7 , the guard unit is positioned so that the screw  94  is located at the opposite end of arcuate slot  90 . With the guard unit in this position, the cutting edge  92  of the knife blade is generally parallel to the direction of elongation of the knife handle, and the handle can be more easily gripped with the cutting edge facing toward the user&#39;s wrist. With the knife handle gripped in this manner, the user can more easily cut workpieces such as rubber roofing sheets from underneath. 
         [0047]    The guard unit  96 , shown in  FIGS. 8-10  is designed for longitudinal adjustment along the knife handle in order to regulate cutting depth. The guard unit  96  comprises a hollow tubular part  98 , shaped to receive the distal part of the handle of knife  100  as shown in  FIGS. 9 and 10 . 
         [0048]    A plate  102  is provided at one end of the tubular part  98 , being connected thereto by welding or other suitable means. The plate has a slot  104  through which the knife blade can extend. The plate can be perpendicular to the direction of elongation of the knife handle, as shown in the drawings. Alternatively, the plate can be oblique to the direction of elongation of the knife handle. The plate is doubly tapered to form guide points  106  and  108  aligned with slot  104 . 
         [0049]    A slot  110  in tubular part  98  extends lengthwise in a direction parallel to the axis of the tubular part  98 , and the guard unit is secured to the knife handle by tightening the head of screw  112  that holds the parts of the knife handle together against the outer surface of tubular part  98 . The guard unit can be positioned with the screw located at one end of the slot as shown in  FIG. 9  for a maximum cutting depth, or with the screw located at the opposite end of the slot for a minimum cutting depth. The screw can also be tightened at any intermediate position in the slot. 
         [0050]    The manner in which cutting depth is adjusted in the embodiment of  FIGS. 8-10  can be applied to another embodiment in which the guard unit is designed for cutting the outer insulation of electrical cables such as heavy, single conductor, electrical cables, coaxial cables, and the like. 
         [0051]    As shown in  FIG. 11 , the guard unit comprises a hollow tubular part  114 , shaped to receive the distal part of the handle of knife  116  as shown in  FIGS. 12 and 13 . A flared, generally U-shaped guide  118  is formed at one end of the tubular part  114 . The U-shaped guide is sized in accordance with the diameter of the cable, and, because of its U shape, maintains alignment of cutting blade  120  of the knife  116  with the axis of the cable during cutting. 
         [0052]    A screw  122 , which holds the two parts of the knife handle together, extends through a slot  124  in the wall of the tubular part of the guard unit. The cutting depth is adjusted by tightening the screw  122  against the outer surface of the tubular part  114 . 
         [0053]    In the embodiment of  FIGS. 11-13 , the U-shaped guide can be configured so that when the cable fits into the guide, the knife handle is perpendicular to the length of the cable. Alternatively, the guide can be configured so that the knife handle is in oblique relationship to the length of the cable. 
         [0054]    The embodiment shown in  FIGS. 14-17 , can be used to cut flexible flooring material such as linoleum or PVC sheets or tiles at the location at which the flooring material meets a vertical wall or baseboard. Handle parts  126  and  128  are secured together to form a knife handle  130 . Handle part  126  is formed as a unit with a guard part  132  and handle part  128  is similarly formed as a unit with guard part  134 . When the handle part  126  and  128  are secured together by screw  136 , guard parts  132  and  134  come together to form a boat-shaped guide having substantially flat surfaces  140  and  142 , which diverge from a knife blade  138  that protrudes through a slot  143  ( FIG. 17 ) located where the surfaces  140  and  142  come together. Surfaces  140  and  142  are perpendicular to each other, and each of them forms an angle of 135° with the blade. Accordingly, when the knife is used to cut flexible flooring sheets or tiles at the location at which the underlying floor meets a wall or baseboard, the knife can be disposed at a 45° angle relative to the wall and floor, with one of surfaces  140  and  142  in engagement with a horizontal part of a sheet or tile of flooring material and the other in engagement with a part of the sheet or tile bent upward against the wall. 
         [0055]    The guard parts  140  and  142  form a boat-shaped structure that can be used to form a crease in flexible flooring material, such as linoleum flooring sheets, when the blade is removed from the knife (or withdrawn in the case of a knife having a retractable blade). The guard parts converge to a point  144 , which can be used as a visual guide, enabling the worker to follow a line drawn on the flooring material while forming a crease in the material. Both when cutting and when forming a crease, the surfaces  140  and  142  aid the worker in maintaining the knife at a 45° angle relative to the floor and wall. 
         [0056]      FIG. 18  shows a modified version of the flooring cutter of  FIGS. 14-17 , in which a utility knife  146  is received in a detachable guard  148  comprising a knife handle-receiving part  150  having and a boat-shaped guide  152  having a pair of surfaces each diverging at an angle of 135° from a blade  154 , which extends through a slot (not shown) in the guide  152 . One such surface is surface  156  in  FIG. 16 . The guide  152  is similar in shape to the two-part guide of  FIGS. 15 and 16 , and has a point  158  that can be used as a visual guide. 
         [0057]    The detachable guard is secured to the knife handle by a screw  160 , which extends through a slot  162 . The slot  162  is elongated in the direction of elongation of the knife handle, enabling the cutting depth to be adjusted by adjustment of the extent to which blade  154  protrudes from the guide.