Abstract:
A tool bit providing a combined drill bit and milling bit is disclosed herein. The tool bit in one embodiment includes a working section having a longitudinally extending central axis, an O-flute extending along the working section, and a tooth formed at a tip portion of the working section, the tooth offset from the central axis.

Description:
[0001]    This patent claims the benefit of U.S. Provisional Application No. 61/330,069, filed Apr. 30, 2010, the entire contents of which are herein incorporated by reference. 
     
    
     FIELD 
       [0002]    This patent relates to the field of drill bits, and more particularly to combination milling and plunge cut drill bits. 
       BACKGROUND 
       [0003]    Drill bits are widely used for drilling holes in various materials, including wood, wood laminates, plastic countertop material, metals, and other natural or artificial materials. Generally, a drill bit may be used to form drill holes in a work piece by plunge cutting into the work piece along the axis of the drill bit. In addition to the ability to drill holes, some drill bits also include the ability to perform other shaping processes. For example, some drill bits are ground to a high precision to provide a reaming function. Other drill bits include cutting features that allow the bit be used as a milling device wherein the drill bit is used to cut in a lateral direction (i.e., a direction perpendicular to the axis of the drill bit). 
         [0004]    Although drill bits with plunge and milling ability in metal have been provided in the past, these combined drill and milling bits have not performed optimally when used to shape plastic materials. For example, many drill bits form ridges and burrs along drilled holes and milled grooves. Additionally, the relative softness of plastics can result in loss of control over the formation of a groove or an axial cut when a bit is used in a hand power tool. Loss of control occurs because a bit can aggressively bite into the soft material. Thus, small perturbations in the angle of attack can generate significant off-axis forces which a user may not be able to control. 
         [0005]    Accordingly, a multipurpose bit including features that stabilize the bit and keep it on line when initially boring into a work piece is desired. A multipurpose bit that produces clean cuts and thus do not result in burring or ridges in softer materials is also desired. A further need exists for a multipurpose bit that is easier to control when shaping softer materials is also needed. 
       SUMMARY 
       [0006]    A tool bit providing a combined drill bit and milling bit is disclosed herein. The tool bit in one embodiment includes a working section having a longitudinally extending central axis, an O-flute extending along the working section, and a tooth formed at a tip portion of the working section, the tooth offset from the central axis. 
         [0007]    In a further embodiment, a tool bit includes a working section having a longitudinally extending central axis, an O-flute extending along the working section toward an upper portion of the working section, a trailing edge defined by a junction of a trailing face and a first upper end portion of the O-flute, a cutting edge defined by a junction of a leading face and a second upper end portion of the O-flute, and a tooth defined in part by the leading face, the tooth extending along the central axis to a location higher than the trailing face. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  depicts a back-side plan view of one embodiment of a combination drilling and milling bit in accordance with principles of the present invention; 
           [0009]      FIG. 2  depicts the combination drilling and milling bit of  FIG. 1  positioned in a hand drilling tool; 
           [0010]      FIG. 3  depicts an enlarged rear perspective view of a boring end of the tool bit of  FIG. 1 ; 
           [0011]      FIG. 4  depicts a top plan view of the tool bit of  FIG. 1 ; 
           [0012]      FIG. 5  depicts a simplified cross-sectional view of the body of the tool bit of  FIG. 1  showing the core of the body. 
           [0013]      FIG. 6  depicts a partial front plan view of the tool bit of  FIG. 1  rotated about ninety degrees from the view of  FIG. 3 ; 
           [0014]      FIG. 7  depicts a partial left side plan view of the tool bit of  FIG. 1 ; and 
           [0015]      FIG. 8  depicts a partial front plan view of the tool bit of  FIG. 1 . 
       
    
    
     DESCRIPTION 
       [0016]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present patent includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
         [0017]    With reference to  FIG. 1 , one embodiment of a tool bit  100  is shown in the form of a combined boring and milling bit. The tool bit  100  includes a shank portion  102 , a working section  104 , and a washout section  106  located between the shank portion  102  and the working section  104 . The tool bit  100  may be made from a carbide material, such as a grade WA2 carbide, so that the tool bit  100  may be used to plunge cut metals and other hard materials. Other materials may be used for other applications. 
         [0018]    The shank portion  102  is configured to engage a power hand drill or other rotating apparatus. Thus,  FIG. 2  depicts the tool bit  100  held in a chuck  120  of a hand drilling tool  122  in preparation for making a plunge cut into a work piece  138 . The working section  104  includes a body portion  108  and an upper portion  110 . The working section  104  includes a body portion  108  and an upper portion  110 . 
         [0019]    The body portion  108  includes an O-flute  112  and a number of relief faces  114  that extend upwardly from the washout section  106  to the upper portion  110 . Both the O-flute  112  and the relief faces  114  extend helically about a central axis  116  of the tool bit  100  in the embodiment of  FIG. 1 . The O-flute  112  and the central axis  116  define a helix angle  118  of the O-flute  112 . In one embodiment, the helix angle  118  is greater than about 25 degrees and preferably between 30 and 35 degrees. In the embodiment of  FIG. 1 , the helix angle  118  is about 33 degrees. 
         [0020]      FIG. 1  depicts the tool bit  100  with a number of relief faces  114 . In other embodiments, more or fewer relief faces may be included, depending on the desired application. By way of example, the tool bit  100  is depicted in  FIG. 3  with 7 relief faces  114 . Generally, about 7-10 relief faces may be provided as desired. 
         [0021]    With reference to  FIGS. 3 and 4 , the upper portion  110  includes a leading face  124  and a trailing face  126 . The leading face  124  forms a cutting edge  128  with an upper portion of the O-flute  112 . The cutting edge  128  extends from the upper portion  110  through the body portion  108 . Within the body portion  108 , an outer periphery  130  and the O-flute  112  define a rake angle  132  as depicted in  FIG. 5 . In one embodiment, the rake angle  132  is about 25 degrees. 
         [0022]    The O-flute  112  is further configured to maintain a core within the body portion  108  of about 60 percent. The “core” refers to the amount of material in the body portion  108  compared to the volume possible for a given effective diameter of the body portion  108 . Thus, in  FIG. 5  the effective circumference of the body portion  108  is identified by the dashed circle  134 . Of the area encircled by the effective circumference  134 , the body portion  108  occupies about 60 percent. The core is thus a function of the relative placement of the O-flute  112  within the effective circumference  134  as well as a depth  136  of the O-flute  112 . In one embodiment, the O-flute  112  has a depth  136  of 1.27 mm within a body portion  108  with an effective radius of 1.5 mm. 
         [0023]    Returning to  FIGS. 3 and 4 , the upper portion  110  further includes a gash  140  that is located between a tooth  142  and a face  144  generally opposite to the leading face  124 . Two faces  146  and  148  are located circumferentially between the leading face  124  and the opposite face  144 . Further description of the upper portion  110  is provided with additional reference to  FIGS. 6-8 . 
         [0024]    The tooth  142  is defined in part by the leading face  124  and extends to a height along the central axis  116  that is higher than the highest portion of the trailing face  126 . An upper edge  150  of the tooth  142  is substantially perpendicular to the central axis  116  when viewed from the left side of the tool bit  100  (see, e.g.,  FIG. 7 ). The tooth  142 , however, is offset from the central axis  116  as shown most clearly in  FIG. 4 . The upper edge  150  and the gash  140  define a gash angle  152  shown most clearly in  FIG. 7 . In one embodiment, the gash angle  152  is about 25 degrees. 
         [0025]    The plane defined by the leading face  124  and the line defined by a junction  154  of the opposite face  144  and the face  146  define a head angle  156  as shown in  FIG. 8 . The head angle  156  is not symmetrical about an axis  158  parallel to the central axis  116 . Rather, a leading angle  160  between the axis  158  and the leading face  124  is smaller than a trailing angle  162  between the axis  158  and the junction  154 . By way of example, in one embodiment the head angle  156  is about 100 degrees with the leading angle  160  being about 40 degrees and the trailing angle  162  being about 60 degrees. 
         [0026]    In operation, the shank  102  of the tool bit  100  is positioned in the chuck of a drill or other rotary tool. The tool causes the tool bit  100  to rotate about the central axis  116  in the direction of the arrow  170  of  FIG. 4 . In order to drill a hole, the user places the upper portion  110  of the tool bit  100  against a work piece, such as a piece of plastic, at a desired location and forces the tool bit  100  toward the work piece. 
         [0027]    The tooth  142  is the highest point of the tool bit  100  along the central axis  116 . Accordingly, as the tool bit  100  contacts the work piece, the tooth  142  makes initial contact with the work piece. Rotation of the tool bit  100  in the direction of the arrow  170  of  FIG. 4  causes the cutting edge  128  along the tooth  142  to sweep a circular path in the work piece. Debris formed by the tooth  142  is directed by the trailing face  126  into the O-flute  112 . Rate of movement of the tool bit  100  into the work piece is controlled by the junction  154  because the trailing angle  162  is larger than the leading angle  160 . In other words, the junction  154  is closer to perpendicular with the central axis  116  than is the face  124 , thus limiting movement into the work piece. Moreover, the large head angle  156  significantly increases the strength of the upper portion  110  which is the portion of the tool bit  100  which normally limits useful life of the tool bit  100  for plunge cuts. 
         [0028]    As the tool bit  100  progresses deeper into the work piece, the cutting edge  128  at the junction of the leading face  124  and the upper portion of the O-flute  112  begins to generate debris. This debris is directed into the O-flute  112 . The O-flute  112  is smooth throughout the body portion  108 . Accordingly, debris is passed smoothly away from the contact area between the cutting edge  128  and the work piece. 
         [0029]    In the event that the user desires to form a grove in the work piece, lateral pressure is applied to the tool bit  100 . The pressure forces the outer periphery  130  of the body portion  108  against the work piece at a lateral working area that extends along the axis  116  of the tool bit  100 . As the O-flute  112  rotates into alignment with the direction of the applied force at the lateral working area, the tool bit  100  is allowed to advance in the direction of the applied force. As the tool bit  100  continues to rotate, the edge formed by the O-flute  112  and the outer periphery  130  rotates into the lateral working area and functions as a lateral cutting edge. The debris generated by the lateral cutting edge is directed into the O-flute and is carried away from the contact area between the tool bit  100  and the work piece. 
         [0030]    The rake angle  132 , along with the amount of lateral force applied by a user, thus affects the aggressiveness with which the tool bit  100  “bites into” the lateral working area of the work piece when the tool bit  100  is used as a milling bit. The advancement of the tool bit  100  into the lateral working area is controlled, however, by the relief faces  114  which contact the work piece at locations adjacent to the O-flute  112  (e.g., above and below the O-flute  112 ) in the lateral working area. Moreover, for a given flute width, the increased helix angle  118  reduces the axial distance between contact points of the relief faces  114  at locations adjacent to the O-flute  112  in the lateral working area. Accordingly, a user has improved control of the movement of the tool bit  100  into the work piece resulting in a smoother cut. 
         [0031]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same should be considered as illustrative and not restrictive in character. It is understood that only the preferred embodiments have been presented and that all changes, modifications and further applications that come within the spirit of the invention are desired to be protected.