Abstract:
A plug cutter is provided that has a main body with a shank extending from one end and plurality of cutting blades extending from the other end. The blades have a plurality of facets defining cutting edges for cutting and shaving stock material to form a plug. The blades define an inner bore having a staged taper and a radial relief portion is provided so that a gap is defined between an outer surface of the plug being formed and the radially relieved portion of the inner surface of the blades. The plug cutter has a built-in depth stop to provide plug height repeatability and quick set up.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a plug cutter and, more particularly, to a plug cutter having a dual taper, radial relief to minimize burning of the outer surface of the plug and to avoid premature plug breakaway, and/or a depth stop for plug height repeatability.  
           [0003]    2. Description of the Related Art  
           [0004]    Conventional plug cutters include a main body portion, a shank extending from one end of the main body portion, and a plurality of cutting tines, or blades, extending axially from an opposite end of the main body. The plurality of cutting blades define a bore that is circular in cross section. The configuration of the bore corresponds to the configuration of the plug produced with the plug cutter.  
           [0005]    Typically, a plug cutter is produced by first, drilling a bore axially into a cylindrical piece of steel and, second, milling the cutting blades out of the resulting annular wall surrounding the bore. Each blade has an inner surface that faces radially inwardly toward the center of the bore.  
           [0006]    Contact by the entire inner surface of the blades on the outer surface of the plug while the plug cutter is rotating can cause burning on the outer surface of the plug due to the heat generated by the high speed frictional contact of the inner surface of the blades with the outer surface of the plug. In addition, friction between the outer surface of the plug and the inner surfaces of the blades can cause a torque to be applied from the plug cutter to the plug, causing the plug to prematurely break away from the stock and become lodged in the bore of the plug cutter. In this case, the plug can only be removed from the plug cutter by destroying the plug. Finally, if the entire inner surface of the blades contact the outer surface of the plug, the outer surface is formed by shearing, rather than cutting, resulting in a plug having a rough outer surface.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention avoids the above-described disadvantages encountered with conventional plug cutters by providing a measure of radial relief between the inner surface of the blades and the circular bore defined by the leading, cutting edges of the blades. The present invention further advantageously defines a dual taper to provide an increased taper at the top periphery of the plug to ensure snug engagement of the formed plug with the bore in which it is inserted. Furthermore, the preferred embodiment of the present invention further provides the unique advantage of an integrated depth stop in the plug cutter bore for providing the plug height repeatability and quick set-up that is highly desirable for woodworking tasks.  
           [0008]    Therefore, according to the present invention, a plug cutter is provided that is rotatable about an axis of rotation. The plug cutter comprises a main body having a longitudinal axis coinciding with the axis of rotation, a shank coaxial with the axis of rotation extending from one end of the main body and a plurality of cutting tines or blades extending axially from the opposite end of the main body. The plurality blades are adapted to cut a plug in a piece of stock material as the plug cutter is rotated at high speed about the axis of rotation and advanced axially into the piece of stock material. In one exemplary embodiment, each blade is formed so that an inner surface thereof defines a dual taper portion adjacent and along a leading edge of the blade, with respect to the direction of rotation, and a radial relief portion downstream of the dual taper portion. The radial relief portion comprises a portion wherein the radial distance from the axis of rotation to the inner surface of the blade is greater than a radial distance to said dual tapered surfaces or to said cutting edge so that as the plug cutter is cutting a plug, substantially only the cutting edge and the dual tapered portions of each blade make contact with the outer surface of the plug. According to a further feature of an exemplary embodiment of the invention, a depth stop is defined within the bore of the plug cutter to limit the height of the plug produced, for plug reproducibility and to avoid plug jamming within the plug cutter. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    These, as well as other objects and advantages of this invention, will be more completely understood and appreciated by careful study of the following more detailed description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:  
         [0010]    [0010]FIG. 1 is a side elevation of a plug cutter embodying the present invention;  
         [0011]    [0011]FIG. 2 is a perspective view from the shank end of the plug cutter;  
         [0012]    [0012]FIG. 3 is a perspective view from the blade end of the plug cutter and;  
         [0013]    [0013]FIG. 4 is an end view of the plug cutter of FIG. 1 taken from the blade end of the plug cutter. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    A plug cutter  10  according to a presently preferred, exemplary embodiment of the invention, is shown in particular in the perspective and elevational views of FIGS.  1 - 3 . Similar to conventional plug cutters, the plug cutter  10  has an axis of rotation  12 , a main body portion  14  having a longitudinal axis which coincides with the axis of rotation  12 , a shank portion  16  extending from a first end of the main body  14  and a plurality of cutting tines or blades  18  extending axially from the other end of the main body. In the illustrated embodiment, the shank  16  has a plurality of facets  20  and is adapted to fit into the jaws of the drill, (not shown) in a conventional manner. In the illustrated embodiment, four blades  18  extend from the main body  14 . As an alternative, the plug cutter may be limited to three blades. The plug cutter is formed as an integrated unit, preferably from stainless steel, but other metals of suitable strength and hardness may be adopted instead.  
         [0015]    As shown in particular in FIGS. 1, 3 and  4 , each blade is formed with a number facets, such as facets,  22 ,  24 ,  26 ,  28 , and  46  as well as cutting edges such as tip  30 . Because each blade  18  of the plug cutter  10  is identically formed, for ease of review and explanation, the corresponding facets and edges of each blade  18  are labeled with the same reference number. As shown in FIGS. 1 and 4, in facet  28  may be disposed in a horizontal plane. It is contemplated, however, that the blades  18  may be formed so that facet  28  does not lie in a horizontal plane and tip  30  is inclined or extends somewhat downwardly.  
         [0016]    In the plug cutter of the present invention, it is presently preferred that the bore defined by the cutting blades be flared or tapered outwardly along at least a portion of the axial length of the bore so that the diameter of the plug cut by the cutting blade is smallest adjacent or near the main body and greatest at or adjacent the cutting tips  30  of the blades  18 . With the blades tapered in this manner, the radius of the leading edge of the blade varies along at least a portion of the axial length of the blade. In a currently preferred embodiment, the blades are tapered along substantially their entire length but at first and second taper angles so that the base of the cut plug which will be the head of the inserted plug is enlarged with respect to the shank of the plug to enhance the tension of the plug in an associated plug hole and to provide for a mating engagement with a modestly countersunk bore configuration.  
         [0017]    More specifically, each blade  18  has an inner surface facing generally radially inward towards the center of the bore defined by the cutting blades, that is towards the axis of rotation of the plug cutter. In an embodiment of the invention, the inner surface of each blade is defined by a plurality of surfaces commencing with and extending circumferentially from a leading edge  32  that extends from tip  30  along the axial length of the blade  18 . As will be appreciated the leading edge of the cutting tip defines the forward most portion of the inner surface with respect to the direction of rotation W as shown in FIG. 4.  
         [0018]    As noted, the leading edge  32  is a cutting edge of the cutting blade. As illustrated, the leading edge is defined in three segments defined by a dual tapered radially inner surface segment of the cutting blade and a dual faceted leading surface of the blade. More specifically, the radially inner surface includes a first portion  34  adjacent the distal tip of the blade which defines a first tapered surface and a second portion  36  proximal thereto which defines a second tapered surface that is tapered less than the first surface  34 . In an exemplary embodiment, the first taper is about 12 degrees with respect to the rotational axis and the second taper is about 4 degrees with respect to the rotation axis.  
         [0019]    The leading, cutting edge  32  is further defined by first and second facets in the leading surface of the cutting blade, leading facet  38  and trailing facet  40 . As best seen in FIG. 1, facets  40  and  36  thus define a first portion of the cutting edge, facets  36  and  38  define a second portion of the cutting edge and facets  34  and  38  define a third portion of the cutting edge.  
         [0020]    The radially inner surface of the cutting blade which trails the tapered portions  34 ,  36  defines a radial relief portion  42 . Thus, at least portion  42  of the inner surface of the cutting blade  18  is provided with a measure of radial relief with respect to the leading edge  32  and with respect to the tapered portions  34 , 36  of the blade inner surface. Thus, as a plug is being cut with the plug cutter, a gap is defined between the plug being cut and the radially relieved portion  42  of the inner surface of the cutting blade. As is apparent from the illustration of FIG. 1, in the illustrated embodiment the radial relief increases gradually to a maximum value at the trailing edge  44  of the cutting blade. Facet  46  defines a transition from the trailing edge  44  to the outer surface of the blade  18  to facilitate debris removal during the cutting operation. While this is a preferred configuration, it is only necessary that a measure of radial relief be provided and the variation in radial relief from adjacent the tapered portions  34 ,  36  of the cutting blade to trailing edge  44  is not critical to realization of the advantages of the invention.  
         [0021]    When a plug is being cut by a plug cutter according to the present invention, substantially only the leading edge  32  and the tapered portions  34 ,  36  of each blade contact the outer surface of the plug being cut while the plug cutter is rotating. This minimal contact between the blade and the plug lessons the amount of burning due to frictional heat and reduces the likelihood that the plug will break off and become lodged in the plug cutter.  
         [0022]    According to a further feature of the invention, as best shown in FIGS. 1 and 4, a depth stop  50  is defined at a predetermined distance L from the distal tip  30  of the cutting blades  18 . In this embodiment, a facet  48  defines a transition from the depth stop to the outer surface of the main body for debris removal. As illustrated in FIG. 4, the depth stop is defined about an entire circumferential periphery of the plug cutter, radially inward of the cutting blades. The depth stop  50  is limited in radial dimension to define a ring that is spaced as shown by surface  52  from the end wall  54  defined within the main body  14 . Thus the depth stop engages the plug being cut about a peripheral edge thereof but not across the entire plug. As a result, a depth stop function is provided without full contact with the plug cutter main body, thus reducing the risk of burning of the tip of the plug and reducing the potential for the plug becoming wedged within the cutting blades of the plug cutter.  
         [0023]    Thus, but for the depth stop  50 , a plug of a greater height than predetermined distance L would be formed by the cutting blades  18 . However, the presence of the depth stop  50  truncates the plug cutting process before the plug extends into the receptacle defined by surfaces  52  and  54 .  
         [0024]    As shown by surfaces  46 ,  48 , the cutting blades actually extend axially a length greater than the predetermined length L defined by the depth stop  50 , and the receptacle defined by surfaces  52  and  54  could accommodate a plug having a height greater than length L.  
         [0025]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.