Abstract:
There is provided a knife attachment that is interchangeable with a saw attachment for a sheet cutting system. The knife attachment has a base plate to which is attached a cutting head that carries a blade holder. The blade holder is adjustable for depth penetration as well as for angle of approach to the work piece.

Description:
FIELD OF INVENTION 
     This invention relates to a sheet cutting system and, in particular, to a knife attachment that is interchangeable with a panel saw attachment for a sheet cutting system. 
     BACKGROUND OF INVENTION 
     Systems for cutting sheet material, such as mat, sheet rock, cardboard, wood panel and the like, have been known for many years. Exemplary mat cutting systems are disclosed in U.S. Pat. Nos. 286,422; 2,835,037; 3,996,827; 3,463,041; 3,964,360; 3,967,519; 4,038,751; 4,867,023; and, 5,272,947. Exemplary large or construction sheet material (for example, 4×8 feet size) cutting systems are disclosed in U.S. Pat. Nos. 3,866,496; 4,058,150, 4,176,572; 4,802,399; and, 5,582,088. 
     The prior art mat cutting systems generally use a knife or blade. The cutting heads that hold these knives range from simple to complex. However, most of these heads are designed for a mat cutting operation and are not durable, easy to manufacture and easy to use in commercial graphic arts and construction type applications. 
     Construction type cutting systems are typified by the aforementioned U.S. Pat. No. 4,802,399 to Olson. This patent discloses an A-frame type support for holding a construction size work piece for cutting by a saw attachment on a carriage. The carriage is arranged for travel on a pair of rails and guide tubes to saw a cut through the work piece. 
     The inventors of the present invention are aware of a knife attachment, Utility Knife Attachment available from Saw Trax Mfg. of Acworth, Ga., for a construction type cutting system. This attachment merely uses an utility knife fastened to a sheet metal bracket. This attachment is not rigid and does not achieve the desired accuracy in use. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a durable knife attachment for commercial graphic arts and construction cutting systems. 
     Another object of the present invention is to provide such a knife attachment that is easy to assemble, easy to use, easy to change blades, and easy to adjust for depth penetration and for blade angle. 
     These and other objects of the present invention are fulfilled by a knife attachment that has a base with a top surface and a bottom surface. The bottom surface faces a work piece which is supported by a frame. The base has a hole extending between its top and bottom surfaces. An elongated blade holder extends through the hole. The blade holder has a first slot extending therethrough and along the length dimension of the blade holder. A mounting plate is adapted to be mounted to the top surface of the base. A structure, such as a screw and a post, is mounted on the mounting plate and is slidably disposed in the first slot to define a depth penetration path along the blade holder length dimension. This allows the blade holder to slide toward and away from the work piece. The screw is preferably a carriage bolt that is operable to lock the blade holder to a desired penetration depth. 
     In another embodiment, a second slot extends through the mounting plate. The carriage bolt is also slidably disposed in the second slot and arranged when tightened to lock the blade holder to both a desired penetration depth and to a desired angle with respect to the work piece. 
     In still another embodiment, a backer board has a third slot. The backer board is disposed behind the work piece with the third slot in alignment with the blade. The backer board gives continuous support to the work piece in the region of the cut and provides a path for the blade during cutting operations. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     Other and further objects, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and: 
     FIG. 1 is a perspective view of the knife attachment of the present invention mounted to a construction type cutting system; 
     FIG. 2 is side view of the cutting head of the knife attachment of FIG. 1; 
     FIG. 3 is an opposite side view of the cutting head of the knife attachment of FIG. 1; and 
     FIG. 4 is a cross sectional view taken along the lines  4 — 4  of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIGS. 1 and 4, there is provided a knife attachment generally represented by numeral  10 . The knife attachment  10  has a base plate  11  with a top surface  17  and a bottom surface  18 . Bottom surface  18  faces a work piece  16 . (Only a portion of work piece  16  is shown in FIG. 1.) Base plate  11  has a hole  12  extending therethrough. 
     A construction cutting system frame  15  is partially shown. By means not shown, frame  15  supports work piece  16  and a pair of spaced apart and substantially parallel guide tubes  13  and  14 . Base plate  11  has extensions  31  and  32  that have U type fasteners  19  for slidably engaging guide tubes  13  and  14  to allow knife attachment  10  to slide along the guide tubes. Knife attachment  10  has a handle  33  to facilitate manual operation in moving it along guide tubes  13  and  14 . 
     A cutting head  20  has a mounting plate  21  that is mounted to top surface  17 . Mounting plate  21  has a first body portion  38  that is substantially parallel to top surface  17  of base plate  11  and fastened thereto by conventional fastener means, such as, for example, screws  37 . Mounting plate  21  also has a second body portion  39  extending at substantially a right angle to body portion  38  and away from base plate  11 . 
     A blade holder  22  has first and second elongated body portions  35  and  36  which are generally perpendicular to top surface  17  and bottom surface  18  of base plate  11 . Blade holder  22  extends through hole  12  toward work piece  16 . A blade  23  is situated in a channel  24  located on one side of first body portion  35  of blade holder  22  and at a distal end from mounting plate  21 . The cutting edge of blade  23  is substantially perpendicular to work piece  16  so as to make a substantially right angle cut therethrough. First body portion  35  of blade holder  22  has a first slot  25  extending therethrough along the length dimension of the blade holder. Second body portion  36  of blade holder  22  is a stiffener to hold first body portion  35  straight and to prevent deflection in use. 
     Mounting plate  21  has a structure, such as an idle post  26  and an adjusting member  27 , extending through its second body portion  39  and into first slot  25  to define a depth penetration path  34  (FIG. 3) along the length dimension of blade holder  22 . Post  26  preferably takes the form of a pin or a carriage bolt that is secured in place and not adjustable. Adjusting member  27  preferably takes the form of a carriage bolt with a hand knob  48  shown in FIGS. 1 and 2. Idle pin  26  and adjusting member  27  are slidably disposed in first slot  25  so that blade holder  22  is adjustable along depth penetration path  34  to a desired depth position at which the adjusting member is manually tightened to lock blade holder  22  to such desired position. In the illustrated embodiment, blade holder  22  and depth penetration path  34  are at substantially a 45° angle with respect to top and bottom surfaces  17  and  18  of base plate  11  and to work piece  16 , and in a plane that is substantially perpendicular to base plate  11  and work piece  16 . 
     The angle of blade holder  22  with respect to work piece  16  can be adjusted in such perpendicular plane. To adjust the angle of blade holder  22  with respect to work piece  16 , second body portion  39  of mounting plate  21  has a second slot  28  that extends therethrough. Adjusting member  27  is slidably disposed within second slot  28  so that the angle of blade holder  22  with respect to work piece  16  is adjustable within limits allowed by the length of the second slot. To select a desired angle, blade holder  22  is moved within second slot  28  to the desired angle and then adjusting member  27  is tightened to lock the blade holder  22  to the desired angle. 
     With reference to FIGS. 1 and 4, a backer board  44  is supported on frame  15  behind work piece  16 . Backer board  44  gives support to work piece  16  in the region where the cut is to be made. Backer board  44  has a slot  45 . Slot  45  is in substantial alignment with blade  23  to provide a cutting channel for the blade during cutting operations. 
     The knife attachment  10  of the present invention is not only durable, but also versatile to cut sheet material having a wide range of thickness (for instance, from on the order of 0.010 inch to on the order of 0.75 inch) and having a wide range of sizes that include 4 by 8 feet and even larger. In addition, the knife attachment  10  can be used in scoring operations on sheet rock, wood panel, hard plastic and the like. 
     The present invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined in the appended claims.