PATENT ABSTRACT
An auger bit includes a shaft having a central axis, a cutting insert mounted to said shaft, and a feed screw that is separate from the cutting insert and which is mounted to the shaft. The cutting insert and the feed screw are engaged with each other. A single locking member, such as a set screw, secures the feed screw member to the shaft, and thereby secures the cutting insert to the shaft. If the feed screw or the cutting insert become worn, feed screw or the cutting insert can be replaced.

PATENT DESCRIPTION
BACKGROUND OF THE INVENTION 
       [0001]    Auger bits have been used to drill holes in utility poles made of wood for a number of years. These auger bits usually have a feed screw near their tip that helps propel the bit through a pole, at least one cutting edge located below the feed screw near the outer circumference of the main shaft of the auger bit that enables the auger bit to cut through the wood, a main shaft with a generally cylindrical shape that has at least one flute that extends from the cutting edge and allows chips formed by the auger bit as it bores into a pole to be removed from the cutting site, and a shank portion that has a diameter that is less than the main shaft that extends from the bottom of the main shaft of the auger bit. 
         [0002]    The shank portion typically has three flats milled about its periphery which allow it to be easily held in a chuck of a powered drill or impact wrench which can be used by the user to cause the auger bit as a whole to rotate. As the auger bit rotates, the threads of the feed screw help to propel the auger bit through the pole, making it easier for the user to complete the boring operation. At the same time, the cutting edges remove material as the auger bit rotates and send this material along the flute of the bit, allowing deep holes to be bored. 
         [0003]    When being used in the field, it is common for an auger bit to hit nails that are within the wooden pole. This can cause damage to the feed screw and cutting edges, impairing the function of the auger bit. For example, the threads of the feed screw could be deformed which prevents the auger bit from self feeding through the pole as it rotates, requiring the user to push and work harder to bore a hole. Likewise, the cutting edges can become chipped or dulled so that they do not efficiently remove wood chips making boring slow. Consequently, a number of techniques have been developed to remedy these problems. 
         [0004]    For example, U.S. Pat. No. 1,389,578 discloses an auger bit that has a replaceable insert that has the feed screw and cutting edges incorporated therein. The replaceable insert can be attached to the shaft of the auger bit using a single screw. This design, however, has two disadvantages. First, the manufacturing the insert is difficult and costly because of the configuration of the replaceable insert because it includes both the feed screw and cutting edges. Second, both the feed screw and the cutting edges are replaced regardless of what features have been damaged on the auger bit, forcing the user to buy and use a replacement insert that is often more costly than necessary. 
         [0005]    U.S. Pat. No. 5,820,319 discloses an auger bit that has replaceable feed screw that is attached to the shaft by means of a single screw. This technique, however, does not provide for any way to replace worn cutting edges. Therefore, this auger bit does not allow the user to handle situations when the cutting edge has become dull. Conversely, U.S. Pat. No. 6,024,520 discloses replacing cutting edges using a screw to attach the replaceable cutting insert to the shaft, but provides no means to replace the feed screw. Thus, neither U.S. Pat. No. 5,820,319 nor U.S. Pat. No. 6,024,520 provides a suitable way to replace both feed screw and cutting inserts, giving the user the needed flexibility to address problems in the field. 
         [0006]    Finally, U.S. Pat. Nos. 4,625,593 and 6,361,255 disclose replaceable feed screws and cutting inserts, but neither show how they can be attached in a quick and effective manner. U.S. Pat. No. 4,625,593 discloses that the insert is brazed onto the shaft making replacement difficult, while U.S. Pat. No. 6,361,255 fails to specify the exact means by which the feed screw and cutting insert are attached in a replaceable manner to the shaft of the auger bit. 
         [0007]    Accordingly, there exists a need for an auger bit that has a replaceable feed screw and a replaceable cutting insert that can be attached in a quick manner, and that allows the user to select which feature needs to be replaced in a cost effective way. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The organization and manner of the structure and operation of the invention, together with further objects and advantages thereof; may best be understood by reference to the following description, taken in connection with the accompanying drawings, wherein like reference numerals identify like elements in which: 
           [0009]      FIG. 1  is perspective view of an auger bit which includes a shaft, an insert and a feed screw, which incorporates the features of the present invention; 
           [0010]      FIG. 2  is a side elevational view of the auger bit; 
           [0011]      FIG. 3  is an alternate side elevational view of the auger bit; 
           [0012]      FIG. 4  is a perspective view of a shaft of the auger bit; 
           [0013]      FIG. 5  is a side elevational view of the shaft; 
           [0014]      FIG. 6  is a cross-sectional view of the shaft along line  6 - 6  of  FIG. 5 ; 
           [0015]      FIG. 7  is an alternate side elevational view of the shaft; 
           [0016]      FIG. 8  is a cross-sectional view of the shaft along line  8 - 8  of  FIG. 7 ; 
           [0017]      FIG. 9  is a cross-sectional view of the shaft along line  9 - 9  of  FIG. 7 ; 
           [0018]      FIG. 10  is an end plan view of the shaft; 
           [0019]      FIG. 11  is a view of the shaft along the view of line  11 - 11  in  FIG. 10 ; 
           [0020]      FIG. 12  is a cross-sectional view of the shaft along line  12 - 12  of  FIG. 10 ; 
           [0021]      FIG. 13  is a side elevational view of the feed screw; 
           [0022]      FIG. 14  is an alternate side elevational view of the feed screw; 
           [0023]      FIG. 15  is a side elevational view of the insert; 
           [0024]      FIG. 16  is a view of the insert along the view of line  16 - 16  in  FIG. 15 ; 
           [0025]      FIG. 17  is an end plan view of the insert; and 
           [0026]      FIG. 18  is an alternate side elevational view of the insert. 
       
    
    
     SUMMARY OF THE INVENTION 
       [0027]    Briefly, the present invention discloses an auger bit which includes a shaft having a central axis, a cutting insert mounted to said shaft, and a feed screw that is separate from the cutting insert and which is mounted to the shaft. The cutting insert and the feed screw are engaged with each other. A single locking member, such as a set screw, secures the feed screw member to the shaft, and thereby secures the cutting insert to the shaft. If the feed screw or the cutting insert become worn, feed screw or the cutting insert can be replaced. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0028]    While the invention may be susceptible to embodiment in different forms, there is shown in the drawings, and herein will be described in detail, a specific embodiment with the understanding that the present disclosure is to be considered an exemplification of the principles of the invention, and is not intended to limit the invention to that as illustrated and described herein. 
         [0029]      FIGS. 1-3  shows an auger bit  20  that has a replaceable cutting insert  22  and a replaceable feed screw  24  attached to a shaft  26  of the auger bit. The cutting insert  22  and the feed screw  24  are attached to the shaft  26  using a single set screw  28 . 
         [0030]    The shaft  26  has a continuous land  30  and flute  32  which extends from a leading end  34  of the shaft  26  to a shank  36  which is provided at a trailing end  38  of the shaft  26 . A central axis  39  extends along the length of the shaft  26  from the leading end  34  to the rearmost end of the shank  36 . The outer periphery of the land  30  is formed as a cutting edge. A groove  40  extends from the cutting insert  22  to the trailing end  36  and allows the removal of chips as the auger bit  20  bores a hole. The shaft  26  has first, second and third passageways first passageway  42 ,  44 ,  46  proximate to its leading end  34  that allow the cutting insert  22 , the feed screw  24  and the set screw  28  to be inserted into the shaft  26 . In addition, a fourth passageway  48  is provided proximate to the leading end  34  of the shaft to allow a user to place an implement within the fourth passageway  50  to force the cutting insert  22  out of the shaft  26  when desired. 
         [0031]    The shank  36  has a smaller diameter than the shaft  26 . The shank  36  has flats  52  thereon which are held in a chuck of a powered drill or impact wrench which can be used by the user to cause the auger bit  20  as a whole to rotate. 
         [0032]    The first passageway  42  forms the passageway into which the cutting insert  22  is mounted. The wall which forms the second passageway  44  is smooth. The first passageway  42  has a central axis  54  that intersects near the edge that would be formed by the leading end  34  and the circumference of the shaft  26 . The central axis  54  forms an acute angle with the central axis  39  of the shaft  26 . Preferably, the acute angle is forty-five degrees which prevents any thin areas that could occur near the leading end  34  of the shaft  26  if the angle were greater, such as ninety degrees. The first passageway  42  terminates at a predetermined distance into the shaft  26  at a floor or stop surface  56 . The depth of the first passageway  42  is great enough so that the first passageway  42  passes through the central axis  39  of the shaft  26 . 
         [0033]    The second passageway  44  forms the passageway into which the feed screw  24  is mounted. The wall which forms the second passageway  44  is generally cylindrical and smooth. The second passageway  44  extends from the leading end  34  of the shaft  26  rearwardly coincident with the central axis  39  of the shaft  26  a predetermined depth. 
         [0034]    The third passageway  46  forms the passageway into which the set screw  28  is mounted. The third passageway  46  is located on the circumference of the shaft  26  at a predetermined distance from the leading end  34 . The third passageway  46  has a central axis  58  that is perpendicular to the central axis  39  of the shaft  26  and intersects the second passageway  44 . Unlike the first and second passageways  42 ,  44  which have smooth walls, the third passageway  46  has an internal thread thereon, such as a ¼-28 internal thread so it can mate with the set screw  28  as fully described herein. The positioning of the third passageway  46  is chosen to make sure that it is not too close to the groove  40  of the shaft  26 , which could compromise the structural integrity of the third passageway  46 . 
         [0035]    The fourth passageway  48  is concentric with the first passageway  42  and extends from the stop surface  56  to the other side of the shaft  26 . The fourth passageway  48  has a smaller diameter than the first passageway  42 . The wall which forms the fourth passageway  48  is smooth. 
         [0036]    The shaft  26  with these features can be made from  1144  stress proof round stock on a multi-tasking lathe such that the outer dimensions are tuned, the passageways  42 ,  44 ,  46 ,  48  are bored or drilled, and the flats  52  are milled. Finally, the groove  40  is milled into the shank  34  using a whirler machine. Since the stock is pre-hardened, no further heat treatment is required. 
         [0037]      FIGS. 13 and 14  illustrate the construction of the feed screw  24 . The feed screw  24  includes a generally conical portion  60  on one end that has male threads thereon. Extending from threaded portion  60  is a stem  62  having a cylindrical shape and a diameter that is less than the threaded portion  60  creating an annular shoulder  64  at the bottom of the threaded portion  60 . The stem  62  has a flat surface  66  proximate to its rear end that forms an acute angle, such as five degrees, with respect to a central axis  68  of the stem portion  62 , such that the depth of the depression created by the flat surface  66  is deepest near the threaded portion  60  and decreases as the flat surface  66  nears the rear end of the stem  62 . The stem  62  is mounted into the second passageway  44 . This construction helps to retain the feed screw  24  within the shaft  26  as described herein. The rear end of the feed screw  24  has a taper  70  that facilitates assembly of the auger bit  20  as will be more fully herein. The feed screw  24  can be manufactured by a cold headed blanking operation out of medium carbon steel to produce the overall shape. Next, the threads can be rolled onto its conical portion  60  and the flat surface  66  can then be milled or ground onto the stem  62 . Finally, the feed screw  24  can be heat treated to forty-five to fifty-five Rockwell scale C. 
         [0038]      FIGS. 15-18  show the cutting insert  22 . The cutting insert  22  includes a generally cylindrical body  72  having first and second ends and a central axis  74 . Three flats  76   a ,  76   b ,  76   c  that form cutting edges  78   a ,  78   b ,  78   c  are formed at one end of the generally cylindrical body  72 . The generally cylindrical body  72  has a shape that corresponds to the first passageway  42  in the shaft  26 . A groove  80  is formed in the generally cylindrical body  72  and has a central axis  82  that forms a forty-five degree angle with the central axis  74  of the generally cylindrical body  72 . The groove  80  mates with a portion of the feed screw  24  as described herein. A chamfer  84  is located around the perimeter of the second end of the generally cylindrical body  72 . The second end forms an abutment surface  86 . The cutting insert  22  can be manufactured out of S-7 tool steel using a screw machine or multi-tasking lathe, such that its general shape is turned and the flats  76   a ,  76   b ,  76   c  and groove  80  are milled thereon. The cutting insert  22  is then heat treated to a range of fifty to sixty Rockwell scale C. 
         [0039]    The auger bit  20  can be assembled in the following manner. First, the user inserts the cutting insert  22  into the first passageway  42  with the abutment surface  86  facing the stop surface  56  of the first passageway  42  until the abutment surface  86  bottoms out on the stop surface  56 . At this point, the cutting insert  22  is free to rotate within the first passageway  42  and the cutting edges  78   a ,  78   b ,  78   c  are located near the edge defined by the front end  34  and the outer wall of the shaft  26 . Next, the user inserts the stem  62  of the feed screw  24  into the second passageway  44  of the shaft  26  located on its front end  34  and pushes the feed screw  24  into the shaft  26  until the taper  70  on the feed screw  24  contacts the cutting insert  22 . At this point, the groove  80  of the cutting insert  22  is not necessarily aligned with second passageway  44  or the stem  62  of the feed screw  24 , so the user usually must rotate the cutting insert  22  until the edge of the groove  80  contacts the stem  62  of the feed screw  24 . Once this happens, the user simply pushes on the feed screw  24  and the taper  70  will rotate the cutting insert  22  until the groove  80  is completely aligned with the stem  62  of the feed screw  24 . Once the annular shoulder  64  bottoms out on the front end  34  of the shaft  26 , the stem  62  has passed completely through the groove  80  of the cutting insert  22  and past the groove  80 , thereby fixing the orientation of the cutting insert  22  and preventing the removal of the cutting insert  22  from the shaft  26 . 
         [0040]    The depth of second passageway  44  is greater than the length of the stem  52 , ensuring that the feed screw  24  can be properly seated with no gaps between its threaded portion  60  and the front end  34  of the shaft  26 . The depth of the first passageway  42  is greater than the distance from the groove  80  of the cutting insert  22  to its abutment surface  86 , ensuring that the groove  80  can properly align the stem  62  of the feed screw  24 , while at the same time the cutting edges  78   a ,  78   b ,  78   c  are located directly next to the groove  40  of the shaft  26  despite any possible dimensional variances due to manufacturing tolerances. The gap between the abutment surface  86  of the cutting insert  22  and the stop surface  56  of the first passageway  42  of the shaft  26  is small enough, e.g. a thirty second of an inch, to minimize the amount of possible misalignment between the groove  80  of the cutting insert  22  and the second passageway  44 , thereby easing assembly. Once the cutting insert  22  and feed screw  24  have been installed, the portions of the cutting edges  78   a ,  78   b ,  78   c  that are nearest the tip of the feed screw  24  in a direction that is parallel to the central axis  39  of the shaft  26  extend past the last thread of the feed screw  24 , helping to make sure that as the auger bit  20  passes through the pole it is pulled through by the threads of the feed screw  24  until the hole is complete, easing the drilling operation. 
         [0041]    The last step in assembling the auger bit  20  is to insert the set screw  28  whose external threads match the internal threads of the third passageway  46  and tighten the set screw  28  until it approaches the stem  62  of the feed screw  24 . The user must then rotate the feed screw  24  so that the flat surface  66  is aligned with the third passageway  46 . Finally, the set screw  28  is tightened until it contacts the flat surface  66 , which due to its angle, exerts some force that urges the feed screw  24  toward a fully seated position. This prevents the feed screw  24  from being extracted from the shaft  26  by the force created by land  30  as the land  30  engages a workpiece or pole. 
         [0042]    Disassembly of the auger bit  20  may be achieved by reversing the above process. Sometimes, debris or slight deformation may cause the removal of the cutting insert  22  to be difficult. Consequently, the fourth passageway  48  allows a user to insert an implement, such as a punch used with a hammer, to dislodge the cutting insert  22  forcibly. 
         [0043]    As can be seen, the auger bit  20  provides an insert  22  and feed screw  24  that can be selectively replaced depending on what damage or dulling has occurred. The auger bit  20  further holds the insert  22  and feed screw  24  in place using a single locking member, set screw  28 . Other locking members are within the scope of the present invention as would be know to one of ordinary skill in the art. Hence, this auger bit  20  satisfies the needs of an auger bit  20  whose features which are subject to wear can be replaced quickly and cost effectively. 
         [0044]    While a preferred embodiment of the present invention is shown and described, it is envisioned that those skilled in the art may devise various modifications of the present invention without departing from the spirit and scope of the appended claims.