Abstract:
The wallboard cutting tool is a compact, handheld device providing a very accurate first cut through the first surface of a sheet of wallboard material normal to a reference edge of the sheet, without additional aids, such as chalk lines, squares, etc. This is accomplished by a truing lip, which is used to true the device normal to the edge of the wallboard, and a pair of rollers that are rotationally fixed to one another. The relatively fixed rollers assure that the device cannot turn to any significant degree while being drawn across the wallboard sheet, thus assuring a straight line cut. A second blade is provided on the end of the tool opposite the first blade for cutting the backing paper opposite the first cut to complete the job. A supplemental retractable tape and/or belt hanger passage may also be provided with the device.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/633,722, filed Dec. 7, 2004. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to hand tools. More specifically, the wallboard cutting tool is configured especially for cutting gypsum wallboard, also known as drywall and sheetrock® (sheetrock is a registered trademark of United States Gypsum Company).  
         [0004]     2. Description of the Related Art  
         [0005]     Gypsum wallboard, or drywall or sheetrock as it is known in the trade, is nearly universally used to finish interior walls and ceilings in building structures. The material is formed of a firm compressed gypsum core with a relatively thin sheet of construction paper applied to each side. The paper adds significant resistance to the sheet against bending and breaking, due to the inelastic nature of the paper. As a result, the customary means used to cut standard size gypsum wallboard panels to a smaller size is to cut through the paper on one side of the board while simultaneously scoring the gypsum core. The core easily breaks along the score line, flexing along the uncut paper opposite the cut. The uncut paper is then cut through along the crease line to complete the cutting of the wallboard sheet.  
         [0006]     Obviously, it is necessary to provide a reasonably accurate cut, i.e., a cut that drifts from a theoretically perfect line by only a fraction of an inch or so in the length of a panel, which can be up to twelve feet in length. If the cut drifts by much more than a large fraction of an inch, the resulting gap between panels or along a corner junction is too large to bridge with seam paper and drywall compound. While such a gap can be filled with a smaller sliver of wallboard, the time and labor required for such a repair can add significantly to the cost of the job if more than a few such repairs are required.  
         [0007]     A number of different devices have been developed in the past to carry out a reasonably straight cut along or across a sheet of wallboard. The problem with most such tools is that when they are constructed to a relatively small size for ease of handling and storage, they lack the straight line accuracy in making a cut on a sheet of wallboard without requiring some additional aid, e.g., a steel tape, square, chalk line, etc. Some larger tools can provide sufficient accuracy, but include integral squares and the like, which results in relatively bulky devices that are difficult to transport and store.  
         [0008]     The present inventor is aware of certain devices belonging to the general family of tools noted above. An example of such is found in German Patent Publication No. 19,827,703, published on Dec. 23, 2000. According to the drawings and English abstract, this device includes a guide that slides along one edge of the wallboard and a cutting wheel extending from the end of an elongate connecting arm, which, in turn, extends from the guide. Another example of such a tool is found in German Patent Publication No. 19,900,248, published on Mar. 9, 2000. According to the drawings and English abstract, this device also includes an elongate arm having a cutting tool at the distal end thereof.  
         [0009]     None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus, a wallboard cutting tool solving the aforementioned problems is desired.  
       SUMMARY OF THE INVENTION  
       [0010]     The wallboard cutting tool is a relatively small, handheld device that fits within the palm and extended fingers of the hand. The device includes a retractable first cutting blade extending from one end thereof, with a truing lip extending across the end normal to the blade. A pair of lateral rollers is also provided, with the rollers having a single axle normal to the plane of the cutting blade and parallel to the truing lip. The two rollers are rotationally affixed to one another, i.e., rotation of one roller forces the opposite roller to rotate at the same rotational speed and direction.  
         [0011]     The device is used by truing the blade normal to an edge of the wallboard sheet by means of the truing lip. The device is then drawn across the wallboard sheet, and travels in a straight line normal to the edge of the sheet due to the restriction from turning by means of the two relatively fixed rollers. Additional straight line stability may be provided by supplementary toothed wheels at each roller, which dig slightly into the paper of the wallboard sheet to provide additional grip. The result is a first cut that is essentially normal to the starting edge of the sheet and that deviates very slightly from the desired straight line, without need for additional aids, such as chalk lines, squares, guide arms, etc.  
         [0012]     A second retractable knife blade is located at the end opposite the first blade, and is used for making the second or finishing cut on the side of the board opposite the first cut. The device may also be provided with a retractable steel tape or other measuring means, if so desired, and/or other accessories. A passage may be provided for hanging the device from a belt stud, rivet, or the like, for convenient storage if so desired.  
         [0013]     These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is an environmental, perspective view of a wallboard cutting tool according to the present invention, showing its positioning at one edge of a wallboard sheet to begin a cut.  
         [0015]      FIG. 2  is a top plan view of the present tool, showing the guide wheels and locations of the two cutting blades.  
         [0016]      FIG. 3  is a section view along lines  3 - 3  of  FIG. 2 , showing details of the two cutting blades. 
     
    
       [0017]     Similar reference characters denote corresponding features consistently throughout the attached drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]     The present invention is a compact, handheld wallboard cutting tool capable of forming relatively accurate and straight cuts along or across a sheet of wallboard without need for additional accessories, such as squares, chalk lines, etc.  FIG. 1  provides a perspective view of the present tool  10 , with  FIG. 2  providing a top plan view and  FIG. 3 a  side elevation view in section to show various details of the tool  10 .  
         [0019]     The cutting tool  10  comprises a hand grip frame  12 , which may be formed of a generally flat sheet of durable material, e.g., steel, etc. The frame  12  is bent to provide the various functions of the present tool  10  and includes a lateral passage for a roller axle, discussed further below. The frame  12  and roller axle passage may be cut from a suitably shaped extrusion or built up from stock components, as desired.  
         [0020]     The frame  12  includes a first end  14  having a first cutting element (e.g., tooth, blade, etc.) therein, and a second end  16  opposite the first end  14 . The first end  14  includes a truing lip  18 , which extends laterally across the end  14  and normal to the length of the frame  12 , and which depends downwardly from the first end  14  of the frame when the tool  10  is positioned atop a sheet of wallboard in working orientation. The lip  18  is placed along one edge E of a sheet of wallboard W, generally as indicated in  FIG. 1  of the drawings. When the lip  18  is in contact with the edge E of the wallboard W along the entire span of the lip, i.e., parallel to the wallboard edge E, the first cutting blade  20  (which is normal to the span of the lip  18 ) is disposed normal to the edge E of the wallboard sheet W, to initiate a first cut that is normal to the wallboard edge E.  
         [0021]     The first blade  20  is most clearly shown in  FIG. 3  of the drawings, with its extended position shown in solid lines and its retracted position shown in broken lines. The first blade  20  is retractably disposed within a first blade housing  22  and passes through a slot  24  centered in the truing lip  18  when the first blade  20  is extended. A first blade extension and retraction slide switch  26  operates atop the first blade housing  22  to selectively extend and retract the first blade  20  as desired, with the switch  26  shown in solid lines for a blade extended position and in broken lines for a blade retracted position in  FIGS. 2 and 3 . The housing  22  is removably secured atop the first end  14  of the frame  12  by a removable rivet or clasp  28 , to allow the housing  22  to be opened for replacement of the first blade  20  as required. The first blade  20  preferably has a smooth, non-serrated edge, as shown in  FIG. 3  of the drawings. Alternatively, a fixed tooth or similar sharp cutting element could be substituted for the retractable first blade  20 , if so desired.  
         [0022]     The frame  12  further includes a laterally disposed roller axle  30 , extending across and below the frame  12  at the opposite end of the first cutting blade  20  from the truing lip  18 . A roller  32  is affixed to each of the opposed ends of the solid roller axle  30 , with the two rollers  32  thus being fixed relative to one another and to the axle  30 . Accordingly, when one of the rollers  32  rotates, the opposite roller  32  must also rotate due to its locked relationship with its opposite member. The rollers  32  have a high traction surface for rolling across the wallboard surface without slipping. This results in the cutting tool  10  tracking straight and true across a sheet of wallboard or the like, as the device is restricted from turning due to the locked relationship of the two rollers  32 . Additional grip between the tool  10  and the wallboard sheet may be provided by an externally toothed wheel  34  rotationally affixed to each end of the axle  30  and/or to each of the rollers  32 . The external teeth slightly penetrate the paper covering of the wallboard to assure an even more positive grip for the tool  10 .  
         [0023]     The present wallboard cutting tool  10  is used by first extending the first cutting blade  20 , and pressing the blade  20  into the edge E of the wallboard W at the desired location to begin the cut. The truing lip  18  is then squared with the edge E of the wallboard W, generally as shown in  FIG. 1  of the drawings. This assures that the first blade  20  is normal to the edge E of the wallboard W, to ensure a straight cut. The roller wheels  32  are placed firmly against the surface of the wallboard W, and the tool  10  is rotated about the roller wheels  32  to raise the truing lip  18  clear of the edge E of the wallboard W. The tool  10  may then be drawn across the surface of the wallboard W, with the first blade element  20  forming a straight cut normal to the edge E of the wallboard sheet W due to the straight track maintained by the two relatively fixed roller wheels  32  and toothed wheels  34 . The accuracy provided by the truing lip  18  and roller wheels  32  assures that the cut will be substantially straight and that it will deviate by no more than a fraction of an inch over several feet.  
         [0024]     The two rollers  32  and the first cutting blade  30  and/or the lowermost edge of the truing lip  18  define a working plane P for the tool  10 , as shown in  FIG. 3 . The rearward portion of the tool frame  12 , i.e., that portion extending from the roller axle  30  to the second end  16 , is angularly displaced above the working plane P by an angle A in order for the hand of the person using the tool to remain clear of the underlying wallboard panel. The portion of the frame  12  adjacent the roller axle  30  may be vertically displaced above the axle  30  as well, for greater clearance.  
         [0025]     The cutting tool  10  is quite compact, and may include additional components and features without unduly affecting its compact nature. For example, a retractable steel measuring tape or the like may be provided adjacent the second end  16  of the frame  12 , if so desired. The tape is indicated by its housing  36 , as shown in  FIGS. 1 and 2  of the drawings, and is conventional with the exception of its integral attachment to the second end  16  of the frame  12  of the tool  10 . Alternatively, the tape could be marked to allow for the length of the frame  12 , if so desired, or some other scale applied thereto.  
         [0026]     Once the first side of the wallboard has been cut and scored, it is broken or snapped along the score line to break the material. At this point, the only thing holding the two portions together is the paper backing on the opposite side of the board from the initial cut. This paper backing is customarily cut with a utility knife or the like along the crease formed by the broken wallboard sheet along its first cut line.  
         [0027]     Generally, the first blade  20  of the present tool  10  is not well suited for cutting through the paper backing opposite the first cut, due to the slight valley formed by the breaking of the wallboard along the score line of the first cut and the width of the truing lip  18  through which the first blade  20  extends only slightly. Additional utility may be provided by the present wallboard cutting tool  10  by including a secondary cutting blade  38  for cutting the paper backing on the side of the board opposite the first cut. This secondary blade  38  may be essentially identical to the first cutting blade  20  described further above, i.e., an off-the-shelf replaceable utility blade having a straight, non-serrated cutting edge, as shown in  FIG. 2 , or may have some other alternative configuration.  
         [0028]     This secondary blade  38  is contained within a housing  40 , and is controlled by a second blade slide switch  42 , which operates essentially like the switch mechanism  26  of the first blade  20 . This permits the second blade  38  to be retracted in order to avoid injury to the hand of the person using the present tool  10 . However, the second blade  38  extends outwardly beyond the second end  16  of the frame  12  in its extended position, as shown in broken lines in  FIGS. 2 and 3 , and its cutting plane is oriented normal, i.e., at right angles, to the cutting plane of the first blade  20 , as shown clearly in  FIGS. 2 and 3  of the drawings. This permits the second blade  38  to easily reach the interior angle of the folded paper backing and cut through the backing to complete the separation of the two portions of the wallboard panel. The second blade  38  is retracted within its housing  40  by drawing the switch  42  toward the first end  14  of the frame  12 , as shown in solid lines in  FIGS. 1 through 3 .  
         [0029]     In conclusion, the present wallboard cutting tool  10  greatly facilitates the cutting of wallboard panels and the like in the field, and will be much appreciated by drywall mechanics and others who have occasion to cut and trim wallboard panels. The ability of the cutting tool  10  to form quite accurate cuts and scores across a wide expanse of wallboard without need for chalk lines, squares, and other guides relieves the user of the need to carry and keep track of such miscellaneous equipment generally needed with other wallboard cutting tools. Yet, the present tool is sufficiently compact and lightweight that it may be carried easily upon a tool holster, belt, or similar article. A keyhole slot  44  or the like may be provided through the frame  12  to facilitate carriage upon a button, rivet, or similar protrusion from such a holster or belt, if so desired. Accordingly, the present tool will prove to be a most versatile, capable, and desirable accessory for all who have need to work with wallboard in the construction field.  
         [0030]     It is to be understood that the present invention is not limited to the embodiment described above, but encompasses any and all embodiments within the scope of the following claims.