Abstract:
A plug cutter is for use in association with a drill, drill press and the like and is for producing a plug. The plug cutter includes a shank, a body portion, an outside cutter and an inside cutter. The shank has a longitudinal axis and is adapted to engage the drill. The body portion is integrally attached to the shank and extends downwardly therefrom. The outside cutter extends downwardly from the body portion and the inside cutter extends downwardly from the body portion and is spaced from the outside cutter. The outside cutter may have an outside cutting edge with a positive rake. The inside cutter may have an inside cutting edge with a positive rake.

Description:
FIELD OF THE INVENTION 
     This invention relates to wood working tools and in particular to tapered plug cutters used to produce wooden plugs. 
     BACKGROUND OF THE INVENTION 
     Wooden plugs are often used to fill round holes in a workpiece to conceal fasteners and screws that have been set below the surface of a workpiece. Generally an overly long wooden plug is applied and glued into the hole to be filled and has its excess trimmed to the surrounding surface height and sanded smooth. Ordinary wooden dowels have been used for this purpose in the past, but as dowels are made with their axis parallel to the grain of the wood and as the end grain of wood accepts stains and finishes differently than the face grain of a piece of wood, it is desirable that plugs be made with their axis at right angle to the grain. When plugs of this type are used, staining and finishing of a workpiece can be achieved with the plugs being almost invisible. Further regarding the staining and finishing of wood, different woods accept stains differently, so it is often desirable that plugs for a workpiece be made from the same wood, or even the same piece of wood, as the workpiece. That being the case, it is desirable that a woodworker have the option of manufacturing their own plugs, and so numerous plug cutters have thus been introduced to provide woodworkers with that option. 
     There are plug cutters are used to produce cylindrical plugs. However a cylindrical plug may result in a gap or a circle of glue between the workpiece and the plug. Accordingly tapered plug cutters have been developed which produce tapered plugs. Tapered plugs are more likely to fit snugly into their holes, to limit the gap around and to provide a good appearance. 
     Some woodworkers have noticed that while tapered plugs improve the fit in holes, they also have the tendency to tip sideways during insertion and so compromise their placement in a workpiece. To limit the amount of movement that occurs when a plug is inserted, some woodworkers prefer to have both a tapered portion, to maintain the tight fit, and a cylindrical portion, to limit the movement during insertion. The cylindrical portion is at the minor diameter end of the tapered portion of the plug. By having the cylindrical portion at the minor diameter end, the cylindrical portion limits the amount of movement the plug can experience when inserted and so keeps the plug correctly oriented. Preferably the cylindrical portion of the plug is of a diameter the same as or very slightly less than the hole to be filled, to gain the greatest movement limiting effect while still fitting in the hole. 
     The cutting characteristics of plug cutters depends on the geometry of the cutting edges of the cutter. It is common to find plug cutters that have a plurality of cutting edges that extend generally radially from the axis of the cutter. This arrangement yields edges that cut the wood with a scrapping action. Alternatively, the cutting edges can be tilted backward from the direction of rotation so as to provide some positive rake to the edge, and so improve the cutting characteristics of the cutter. 
     During the operation of a plug cutter, it is recommended that the work be conducted in a drill press, as opposed to a hand held drill, as the forces on the cutter tend to cause considerable wandering tendencies. This wandering tendency is greatest while starting to cut a plug and decreases when the cutter has moved into the stock, but is substantial enough that use of the cutter in a hand held drill is difficult. The larger the diameter of the formed plug, the more pronounced the wandering tendencies and so the more difficult and dangerous the exercise becomes. The use of a drilling guide, to align and steady the cutter, can make hand forming of plugs possible, but the process is slowed down as the guide has to be clamped to the stock and moved for each plug that is formed. 
     Once the plug has been formed in the stock, it is detached either by prying and snapping it from the stock, for example with a screwdriver, or by cutting it from the stock with a saw, by cutting across the lower portion of the plug. 
     Several plug cutters have been developed to manufacture tapered plugs with cylindrical portions. U.S. Pat. No. 5,213,456 issued to Lee on May 25, 1993 shows a cutter that will form a tapered plug having a cylindrical portion at the minor diameter end of the tapered portion. Similarly, U.S. Pat. No. 5,401,125 issued to Sevack et al. on Mar. 28, 1995 shows a cutter that forms plugs having a cylindrical portion at the minor diameter end of a generally flared body portion, the flared body portion providing improved fit and alignment during insertion over cylindrical and tapered plug performance. Additionally, the Sevack cutter shows a hole through the shank that may be used to eject plugs that have sheared off from the stock during forming of the plug, allowing for improved removal of sheared plugs. U.S. Pat. No. 5,810,524 issued to Wirth et al. on Sep. 22, 1998 shows a cutter that has clearance applied to the inner surfaces of its cutting edges to minimize the contact between the cutter and the plug. 
     Despite these and many other improvements to plug cutters there still remain deficiencies and it is the ambition of this invention to overcome these deficiencies. In particular it would be advantageous to have a plug cutter that forms tapered plugs, having a cylindrical portion, that has good cutting characteristics, increased clearance between the cutter and the formed plug and increased ease of removing a sheared plug from the cutter. 
     SUMMARY OF THE INVENTION 
     The present invention is a plug cutter for use in association with a drill, drill press and the like and is for producing a plug. The plug cutter includes a shank, a body portion, an outside cutter and an inside cutter. The shank has a longitudinal axis and is adapted to engage the drill. The body portion is integrally attached to the shank and extends downwardly therefrom. The outside cutter extends downwardly from the body portion and the inside cutter extends downwardly from the body portion and is spaced from the outside cutter. The outside cutter may have an outside cutting edge with a positive rake. The inside cutter may have an inside cutting edge with a positive rake. 
     In another aspect of the invention a plug cutter is for use in association with a drill, drill press and the like and is for producing a plug. The plug cutter includes a shank, a body portion, a plurality of blades and a shoulder. The shank has a longitudinal axis and is adapted to engage the drill. The body portion is integrally attached to the shank and extends downwardly therefrom. The plurality of cutting blades extend downwardly from the body portion and are adapted to cut a plug. The shoulder extends outwardly from the body portion and is adapted to limit movement of the plug cutter into a workpiece. 
     In a further aspect of the invention a plug cutter is for use in association with a drill, drill press and the like and is for producing a plug. The plug cutter includes a shank, a body portion, a plurality of blades and a cavity. The shank has a longitudinal axis and is adapted to engage the drill. The body portion is integrally attached to the shank and extends downwardly therefrom. The plurality of cutting blades extend downwardly from the body portion and are adapted to cut a plug. The cavity is formed in the body portion to provide access to a top of a plug. 
     Further features of the invention will be described or will become apparent in the course of the following detailed description. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described by way of example only, with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of the tapered plug cutter constructed in accordance with the present invention, shown with a plug; 
     FIG. 2 is a front view of the tapered plug cutter of FIG.  1 : 
     FIG. 3 is a first side view of the tapered plug cutter of FIG. 1; 
     FIG. 4 is a back view of the tapered plug cutter of FIG. 1; 
     FIG. 5 is a second side view of the tapered plug cutter of FIG. 1; 
     FIG. 6 is an end view of the tapered plug cutter of FIG. 1; 
     FIG. 7 is a side view of the tapered plug cutter engaged in a work piece at full depth of cut, the cutter and the work piece shown in section; 
     FIG. 8 is perspective view of an alternative embodiment of the tapered plug cutter of the present invention having an outside cutter that contacts the plug at its inside surface; and 
     FIG. 9 is the tapered plug cutter of FIG. 8 shown engaged in a work piece at full depth of cut, the cutter and the work piece shown in section. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The plug cutter of the present invention is a cutter for forming tapered plugs in a wooden work piece. The cutter  10  is shown in FIG.  1  and has a shank  12 , a body portion  14 , an outside cutter  16 , inside cutter  18  and a clearance cavity  20 . The tapered plug  22 , also shown in FIG. 1, formed by the cutter  10  has a tapered portion  24  and a cylindrical portion  26 , such that the cylindrical portion  26  is at the minor diameter end of the tapered portion  24 . A shoulder  28  extends around the perimeter of the cutter  10  between the body portion  14  and the cutters  16  and  18 . The shoulder  28  extends radially beyond the outer limits of both the outside cutter  16  and the inside cutter  18  such that it acts like a depth stop during operation of the cutter  10 . 
     Shown in FIGS. 2 to  5  are the four sides of the cutter  10  and shown in FIG. 6 is an end view of the cutter  10 . In these figures, the inside cutting edge  30  of the inside cutter  18  is shown to be tapered, and it is this cutting edge that forms the tapered portion  24  of the plug  22 . Further, the inside surface  32  of the inside cutter  18  also is a tapered surface that contacts the plug  22  when forming the plug  22 . Additionally, the outside cutting edge  34  of the outside cutter  16  is shown to be tapered. It is the outside cutting edge  34  that cuts the outer boundary of the annular groove formed when cutting a plug  22 . The inside surface  36  of the outside cutter  16  establishes a surface that is at a radius from the longitudinal axis  37  greater than any portion of the inside cutting edge  30 . Preferably, no part of the inside surface  36  of the outside cutter  16  contacts the plug  22  during formation of a plug  22 . FIG. 7, showing a section through both the cutter  10  and the work piece  42 , shows the clearance between the plug  22  and the inside surface  36  of the outside cutter  16 . Also shown in that figure is the clearance established between work piece  42  and the outer surfaces  38  and  40  of the inside cutter  18  and the outside cutter  16  respectively. 
     Preferably, the tips of the cutters  16  and  18  have bevelled ends where, although it is shown in the figures that the outside cutter  16  end is sloped away from the longitudinal axis  37  and the inside cutter  18  end is sloped toward the longitudinal axis  37 , it is recognized that as long as one of the cutters has an end that is sloped toward the longitudinal axis  37 , satisfactory plug  22  formation will occur. The provision that at least one of the ends be sloped toward the longitudinal axis  37  establishes a stress concentration when plug  22  is removed from the work piece by outward prying as with a screw driver. 
     Additionally FIG. 7 shows a formed plug  22  that has a tapered portion  24  and a cylindrical portion  26 . The plug  22  has not been detached from the work piece but the cutter  10  is shown at its finished depth of cut. The finished depth of cut is determined when the shoulder  28  engages the upper surface of the work piece  42  and so limits further cutting and downward movement of the cutter  10 . 
     The location and diameter of the clearance cavity  20  determines the upper limit of the inside cutting edge  30  and that determines the proportion of the plug  22  that it tapered  24  versus cylindrical  26 . Additionally, the location of the shoulder  28  in relation to the clearance cavity  20  and the inside cutting edge  30  determines where the cutting action stops and thus determines the proportion of tapered  24  to cylindrical  26  portions of the finished plug  22 . 
     The inside cutting edge  30  and the outside cutting edge  34  are each established to provide a measure of positive rake to the cutting action of each of those cutting edges. The provision of positive rake  31  and  35  to the cutting edges  30  and  34  respectively allows each edge to cut more efficiently or to cut using less torque. As the cutting action to form a tapered plug  22  requires that an entire side of the tapered plug  22  be cut at a time, as opposed to the cutting of an annular groove for the formation of a cylindrical plug, considerable torque must be applied to the cutter  10 . Further, as the torque applied to the cutter  10  is the same as the torque that must be resisted by the work piece  42  in order for cutting action to develop, only limited torque can be tolerated by the work piece  42 . The cross sectional area at the base of a formed plug  22  is limited by the diameter at the base, so too the torque resisting capacity of the work piece  42  is also limited. Often prior art plug cutters have a plurality of cutters each forming both the tapered portion of the plug and the outer boundary of the annular groove, so that the effective rake angle is zero. Further in use such cutters often shear the plugs at their base during the formation process. This is the case as the work piece can not resist the torque required to cut, so the plugs shears from the work piece. In the case of plug cutters where each individual edge has to perform cutting action on two sides, the plug side and the annular groove side, the rake angles of both edges end up being zero. Any attempt to provide positive rake to one edge causes the other edge to have negative rake, so both edges set at zero rake is often settled for. In an effort to reduce the frequency of sheared plugs, efficient cutting positive rake geometry has been designed into the cutter  10 . As the cutter  10  of the present invention has a designated outside cutter  16  and a designated inside cutter  18 , there is sufficient opportunity to apply considerable positive rake to each cutter  16  and  18  without compromising the performance of the other. 
     An additional advantage of the cutter of the present invention over the prior art, is in the provision of the clearance cavity  20 . The cavity  20  offers a point of inspection in the instance where a portion of a formed plug has broken off and has jammed between the cutters  16  and  18 . As the cavity  20  extends to the perimeter of the cutter  10 , it is easy enough to look in the cavity  20  to see if debris is indeed lodged therein. Prior art cutters having the cutting edges surrounding the central bore require that the operator look up the bore for inspection purposes, something that can be trying if the cutter remains in the chuck of a drill press. Similarly, the cavity  20  offers the opportunity to eject sheared plugs from the cutter  10  by means of a screw driver or similar tool. The ejection of sheared plugs being easier when access to the top of the sheared plug is possible as with the cutter of the present invention, as opposed to having to dig the broken plug out as in the case of prior art cutters. 
     An alternative embodiment of the plug cutter of the present invention is in the form of a tapered plug cutter  44  shown in FIGS. 8 and 9. In this embodiment of the cutter, a cutter  44  is provided that is similar to the previously disclosed cutter  10  except for the provision of an inside surface  46  to outside cutter  48  that has not been thinned to reduce the amount of contact with the formed plug  22 . The advantage obtained for providing an inside surface  46  to outside cutter  48  that engages the plug  22  during formation of the plug  22  is the reduced vibration that may develop. As the forces and amount of contact is equal or balanced on both sides of the formed plug  22  there is reduced likelihood of vibration between the cutter  44  and the plug  22 . The advantage of reduced vibration must be weighed against the disadvantage of increased friction and heat build up. 
     It will be appreciated that the above description relates to the invention by way of example only. Many variations on the invention will be obvious to those skilled in the art and such obvious variations are within the scope of the invention as described herein whether or not expressly described.