Abstract:
A rotary, tubular hole cutter for quickly cutting holes through materials such as wood, fiberboard, and drywall. The device includes a tubular member with a backing plate attached to one end, with holes in the backing plate that enable the attachment of a conventional heavy-duty hole saw arbor. The device includes three equally spaced gullets, each of which has a cutting bit mounted adjacent to the trailing edge of the gullet, with the cutting face lying in the direction of rotation. The combination of three gullets and cutting bits, along with the cutting bit geometry, enable fast extraction of the “puck” or core from the tubular member after the cut is completed, by hand or other suitable device. The nature and aggressiveness of the cutting action is limited by the geometry of the cutting bits and their relationship to the top surface of the tubular member.

Description:
This application claims priority from a Provisional Application, Serial No. 60/312,388, filed Aug. 15, 2001. 
    
    
     FIELD 
     The present invention relates to tools, and, more specifically, to devices for cutting holes in wood and other construction materials. 
     BACKGROUND 
     Hole cutting devices for use in the construction trades typically consist of hole saws, auger bits, and spade-type bits. Several limitations are inherent in these traditional devices, such as cleanliness of cut, speed of cut, ability to cut large diameters with relatively low torque, and the ability to cut an interrupted or partial hole. Because of the proliferation of battery powered drilling devices, tools that cut large diameter holes without stalling or exceeding the torque capabilities of these devices have not been available. Also, as with rehabilitation construction, sometimes there are nails or screws hidden in the work piece that can fatally damage the saw or bit&#39;s cutting edge. 
     Previous attempts at solving these problems have been only marginally successful. For example, a hole saw shown in U.S. Pat. No. 5,803,677 to Brutscher et al. (“Brutscher”) probably provides a fast cut, but the raker teeth provided on the hole saw add additional torque, and the hole saw, because of the number and placement of cutting teeth, does not offer an ideal load distribution and balance. 
     Further, in U.S. Pat. No. 5,597,274 to Behner (“Behner”), a hole cutter has a single cutting bit for reducing torque. However, the single-bit design adds to undesirable wobble and instability, as well as to a slower cutting speed. 
     Accordingly, a primary object of the present invention is to provide a tubular hole cutter that has an optimized cutting load distribution, and that offers a fast, low torque, clean cut, even for large-diameter and interrupted or partial holes. 
     SUMMARY 
     A tubular hole cutter comprises a tubular side wall and a circular backing plate attached to one end of the tubular side wall. The backing plate is configured for attachment to a conventional heavy-duty hole saw arbor. At an end opposite to the backing plate, the tubular side wall has a generally smooth, annular end surface interrupted by three gullets extending longitudinally in the side wall parallel to the axis of the hole cutter. The gullets are spaced equally about the circumference of the tubular side wall. Three cutting bits are attached to the tubular side wall at respective trailing edges of the gullets, i.e., spaced equally apart by 120°, with one cutting bit per gullet. This configuration allows the tubular hole cutter to place a maximum force, transferred to the object under the cutting edges, without binding the tool or resulting in an undesired angled offset hole. Additionally, the cutting bits are configured, according to a particular geometrical design, to produce a smooth, balanced, and precise cut, to reduce torque, and to reduce cutting bit wear, among other things. 
     In use, initially, the hole cutter is attached to a hole saw arbor, and the arbor is affixed to a drill or other power tool. The central pilot drill bit from the arbor engages the work piece to provide a stabilizing hole until the cutting bits engage the work piece. The outer edges of the cutting bits are configured to contact the work piece first, causing a scoring action that greatly reduces any rough surface at the entry and exit of the cut. This also creates a lip or flange on the exit side of the cutout, or “puck,” that causes the puck to resist being drawn all the way into the hole cutter, thus allowing the puck to be more easily removed. During cutting the chips generated by the cutting bits are ejected into the gullets. Once the cutting operation is finished, the puck produced by the cut is then easily removed by hand or with a screwdriver or similar tool. 
     The multiple cutting bits share a reduced chip load resulting in lower cutting torque. The combination of multiple cutting bits, the shape of the bits, and the limitation of the depth-of-cut of the cutting bits by the annular end surface between the gullets provides a stable, low torque cut, even with larger diameters. This is especially desirable when using battery operated drilling devices. 
     When drilling an interrupted or partial (i.e., semi-circular) hole, the equally-spaced multiple bits facilitate continuous engagement with the work piece even when cutting with as little as about 52% of the surface diameter of the tubular hole cutter. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a tubular hole cutter, according to the present invention; 
     FIG. 2A is side elevation view of a cutting bit portion of the tubular hole cutter; 
     FIG. 2B is a front elevation view of the cutting bit shown in FIG. 2A; 
     FIG. 2C is a top plan view of the cutting bit shown in FIG. 2A; and 
     FIG. 3 is a schematic, cross-sectional view of a work piece and a cutout or “puck” produced by cutting a hole through the work piece with the tubular hole cutter. 
    
    
     DETAILED DESCRIPTION 
     With reference to FIGS. 1-2C, a tubular hole cutter  10  according to the present invention comprises a circular backing plate  12  and an open-ended, tubular side wall  14  attached to the backing plate  12  at one end. At an end opposite to the backing plate, the tubular side wall  14  has a generally smooth, annular end surface  16  interrupted by three gullets  18  extending longitudinally in the side wall  14  parallel to the axis of the hole cutter  10 . The gullets  18  are equally spaced about the circumference of the tubular side wall  14 . Three cutting bits  20  are respectively attached to notches  22  in the gullet trailing edges  24 , and are correspondingly spaced apart from one another by about 120°. This configuration allows the tubular hole cutter to place a maximum force, transferred to the object under the cutting edges, without binding the tool or resulting in an undesired angled offset hole. Thus, the present invention provides a reliable and safe cutting process by using the physics of triangulation to equally distribute the load about the tool circumference. Additionally, as discussed in more detail below, the cutting bits are configured to produce a smooth, balanced, and precise cut, to reduce torque, and to reduce cutting bit wear. 
     The tubular hole cutter  10  is meant to be turned in the counter clockwise direction of rotation  26  when viewed from the perspective of the open end of the tubular side wall  14 . 
     The backing plate  12  is equipped with an attachment means, namely, a threaded, central hole  28  and at least two drive-pin holes  30 , for attaching the hole cutter to a conventional heavy-duty hole saw arbor. More specifically, the tubular hole cutter  10  is for use in combination with a standard hole saw arbor (not shown), of the type typically having a pilot drill of sufficient length to extend longitudinally along the hole cutter&#39;s axis far enough to reach past the cutting bits  20 . Such hole saw arbors are typically driven by a standard electrical drill or other suitable device. 
     FIGS. 2A-2C show the particular shape and configuration of the cutting bits in greater detail. The cutting bits are substantially identical to one another, i.e., they are identical within manufacturing tolerances. The cutting bits  20  are attached to the notches  22  in the gullet trailing edges  24  at an angle α (see FIG. 2A) that generally extends in the direction of rotation  26 , i.e., cutting face portions  32  of the bits  20  are angled forward at a rake angle α to extend past the gullet trailing edges. In a preferred embodiment, the rake angle a extends from 0.0 degrees to 45.0 degrees, with the preferred angle for cutting wood being at about 15.0 degrees, to control the amount to shear of wood (i.e., the amount of shear on the bit). 
     Further, each cutting bit  20  terminates at a cutting edge  34 . The cutting edge  34  extends longitudinally beyond the annular end  16  of the tubular side wall  14  by a distance L 1  of at least 0.005 inches (0.013 cm), with a preferred embodiment extending between 0.010 and 0.020 inches (0.025 to 0.051 cm), to control the depth of penetration into the work piece and to also reduce torque. 
     The cutting edge  34  also has a top bevel grind (see FIG. 2B) descending in the direction from the outer diameter of the tubular side wall  14  towards the center of the tubular side wall  14 . The top bevel grind is angled at an angle β of between 0.0 degrees to 45.0 degrees, with a preferred embodiment being angled by β=5.0 degrees, to create a score at the circumference for a cleaner cut hole. With reference to FIG. 3, this also creates a lip or flange  36  on the exit side of the “puck”  38  (the cutout portion of the work piece  40 ) to prevent it from being drawn all the way into the cutting device, thereby facilitating its easy removal. 
     The cutting bits  20  also have a back clearance or top relief  42  extending from the cutting edge  34  back toward the gullet trailing edge  24  at an angle χ of 0.0 degrees to 45.0 degrees, with a preferred embodiment having a top relief of χ=5.0 degrees, to control the speed of the penetration of the cut. 
     The cutting bits  20  also have side clearances or reliefs  44 ,  46 , each with a minimum angle Δ of 2.0 degrees, to reduce friction, torque, and side wear of the cutting bits. It should be noted that the side reliefs do not necessarily have to be angled the same. 
     Further, the cutting bits  20  have an “outer” radial relief  48  (see FIG. 2C) extending from the outer edge of the bit cutting face  32  to the outer surface of the tubular side wall  14  (or thereabouts), and an “inner” radial relief  50  extending from the inner edge of the bit cutting face  32  to the inner surface of the tubular side wall  14  (or thereabouts). Each radial relief  48 ,  50  is angled at a minimum angle φ of 3.0 degrees to reduce torque and corner wear. Again, the radial reliefs can be angled differently from each other. 
     The tubular side wall  14  is made from steel generally 0.100 inches (0.254 cm) in thickness. The cutting bits  20  are slightly wider, generally about {fraction (3/16)} inches (0.476 cm) in width, allowing for the cutting edge  34  to cut a path larger than the width of the end surface  16  of the side wall  14 . Additionally, the side wall  14  is of sufficient depth to enable the hole cutter  10  to cut through a significant thickness of wood or construction material. Generally, this would represent a cut depth of about 2¼ inches (6 cm) typically encountered in most construction and rehabilitation settings. 
     The gullets  18  are each about 0.5 inch (1.3 cm) wide. This has been found to provide a good balance between having enough space for ejecting cut chips and structural and operational stability. 
     In use, initially, the hole cutter  10  is attached to an arbor and drill. The central pilot drill from the arbor first engages the work piece to provide a stabilizing hole until the cutting bits  20  engage the work piece. The outer edges of the cutting bits  20  (i.e., the radially-outermost portions of cutting edges  34 ) contact the work piece first, causing a scoring action that greatly reduces any rough surface at the entry and exit of the cut. This also creates the lip or flange  36  on the exit side of the “puck” or “slug”  38  that causes the puck to resist being drawn all the way into the hole cutter  10 , thus allowing the puck to be more easily removed. The chips generated by the cutting bits are ejected into the gullets. 
     The multiple cutting bits  20  share a reduced chip load resulting in lower cutting torque. The combination of multiple cutting bits and the limitation of the depth-of-cut of the cutting bits by the annular end surface  16  between the gullets provides a stable, low torque cut, even with larger diameters. This is especially desirable when using battery operated drilling devices. 
     Once the cutting operation is finished, the puck or slug produced by the cut is then easily removed by hand, or by using a screwdriver or other suitable device in any of the multiple gullets or combination thereof. 
     The three cutting bits  20 , spaced equally apart by 120 degrees, in conjunction with the particular shape and positioning of the cutting bits  20 , provide significant performance advantages over prior art hole cutters. These advantages include: 
     optimized cutting load distribution; 
     lower friction and required torque load (from 10 to 30 percent lower than standard hole saws), facilitating use with battery powered drills; 
     faster, cleaner cuts; 
     longer tool life, including reduced side wear and corner wear; 
     the ability to cut through small metal objects (e.g., screws, nails), hidden in a work piece, without damage; 
     enhanced safety because of low torque and less fatigue; 
     easy puck extraction by hand or with a tool; and 
     when drilling an interrupted or partial hole, the equal spacing of the multiple bits facilitates engagement with the work piece, even when cutting as low as approximately 52% of the surface diameter of the device. 
     To further illustrate these advantages, a 4 inch (10 cm) diameter version of the present invention was tested against a standard 4 inch diameter hole saw, i.e., of the type having a tubular side wall or member that terminates at an annular ring of contiguous cutting teeth (see FIG. 1 in Brutscher). The same electric drill was used to cut holes into a wood panel using the two bits. Results were tabulated by tracking the electrical current (in amps) drawn by the drill during the cutting procedure. Results are given in the table below: 
     
       
         
               
               
               
             
           
               
                   
               
               
                   
                 CURRENT DRAWN 
                   
               
               
                 STAGE OF 
                 BY DRILL USING 
                 CURRENT DRAWN BY 
               
               
                 CUTTING 
                 PRIOR ART 
                 DRILL USING PRESENT 
               
               
                 OPERATION 
                 HOLE SAW (AMPERES) 
                 INVENTION (AMPERES) 
               
               
                   
               
             
             
               
                 No load 
                 1.4 A 
                 1.4 A 
               
               
                 Full load, 
                 4.1 A 
                 2.3 A 
               
               
                 approximate 
               
               
                 minimum draw 
               
               
                 Full load, 
                 6.9 A 
                 4.3 A 
               
               
                 approximate 
               
               
                 maximum draw 
               
               
                   
               
             
          
         
       
     
     As should be appreciated, these results show that when using the same drill to cut into the same wood, a hole saw according to the present invention draws significantly less current than a standard prior art hole saw. 
     The numerical ranges set forth above for the various cutting bit features (e.g., 25 the cutting edge 34 extending longitudinally beyond side wall by a distance L 1  of at least 0.005 inches) have been experimentally and/or theoretically validated as being suitable for bringing about the various, respective functions associated therewith (e.g., controlling penetration depth and reducing torque). Additionally, optimum values or ranges (e.g., L 1 =between 0.010 and 0.020 inches) have been experimentally and/or theoretically validated as optimizing said functions. 
     The cutting bits  20  have been illustrated as single piece, generally trapezoidal solids (i.e., slightly irregular, six-sided solids, with each side being generally planar and having four edges). However, other overall bit shapes are possible, e.g., curved sides, provided they supply some or all of the various reliefs, extensions, rake angles, etc., according to the present invention, as set forth above and in the claims. 
     Although the tubular hole cutter of the present invention has been illustrated for use with a conventional hole saw arbor, one of ordinary skill in the art will appreciate that the tubular hole cutter could be configured for use without an arbor, or it could be provided with its own, “built in” arbor (i.e., a forwards extending drill bit attached to the center of the backing plate and coaxial with the tubular side wall, and corresponding shank extending rearwards from the backing plate). 
     Since certain changes may be made in the above-described tubular hole cutter, without departing from the spirit and scope of the invention herein involved, it is intended that all of the subject matter of the above description or shown in the accompanying drawings shall be interpreted merely as examples illustrating the inventive concept herein and shall not be construed as limiting the invention.