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CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/379,223 titled “Auger with Butterfly Flighting,” filed on Sep. 1, 2010, the entire contents of which are herein incorporated by reference. This application further claims the benefit of U.S. Provisional Application No. 61/507,146 titled “Post Hole Digger,” filed on Jul. 13, 2011, the entire contents of which are herein incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the field of digging devices, and more particularly relates to an auger for drilling holes. 
       BACKGROUND AND SUMMARY OF THE INVENTION 
       [0003]    A post hole auger for drilling holes in soil is provided. In one embodiment, the auger is powered by a power take-off (PTO) of a tractor. 
         [0004]    Prior art tractor-based post hole augers are generally continuous-flighting augers. “Flighting” refers to the helical blade extending from the rotating shaft of traditional flighted augers. Continuous-flighting augers are efficient at drilling holes because the “flights” move soil up out of a hole as the hole is drilled. However, continuous-flighting auger-based post hole diggers have been the cause of serious accidents and even fatalities due to the flighting on the rotating auger shaft catching clothing, hair, or body parts of individuals who may be in the digging area. 
         [0005]    An auger according to the present disclosure does not have continuous helical flighting on the auger shaft. The cutting head of the auger comprises a generally flat blade disc with a plurality of cutting blades affixed to the disc. An auger tip extends below the disc. A generally butterfly-shaped flighting extends from the auger shaft and is positioned above the cutting head, but does not extend continuously along the auger shaft. In operation of the auger, a column of soil accumulates on a top surface of the flat blade disc for removal from the hole. The flighting “lightens” the column of soil that accumulates to enable a higher column to accumulate on the flat blade disc. Because the flighting is relatively small (in relation to continuous-flighting augers) and is usually below the ground during post hole digging operations, the auger may be less susceptible to accidents caused by flighting on the rotating shaft. 
         [0006]    For purposes of summarizing the invention, certain aspects, advantages, and novel features of the invention have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any one particular embodiment of the invention. Thus, the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The disclosure can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the disclosure. Furthermore, like reference numerals designate corresponding parts throughout the several views. 
           [0008]      FIG. 1  is a side plan view of a post hole digger according to an exemplary embodiment of the present disclosure. 
           [0009]      FIG. 2  is a bottom perspective view of an auger according to an exemplary embodiment of the present disclosure. 
           [0010]      FIG. 3  is a top perspective view of the auger of  FIG. 2 . 
           [0011]      FIG. 4  is an enlarged partial side view of the auger of  FIG. 2 . 
           [0012]      FIG. 5  is a top plan view of the auger of  FIG. 2 . 
           [0013]      FIG. 6   a  is a front plan view of the blade mount angle of  FIG. 4 . 
           [0014]      FIG. 6   b  is a side plan view of the blade mount angle of  FIG. 4 . 
           [0015]      FIG. 7   a  is a front plan view of the blade mount bar of  FIG. 4 . 
           [0016]      FIG. 7   b  is a side plan view of the blade mount bar of  FIG. 4 . 
           [0017]      FIG. 8   a  is a front plan view of the blade of  FIG. 4 . 
           [0018]      FIG. 8   b  is a side plan view of the blade of  FIG. 4 . 
           [0019]      FIG. 8   c  is front plan view of an alternative embodiment of the blade of  FIG. 4 . 
           [0020]      FIG. 9  is bottom plan view of a blade disc according to an exemplary embodiment of the present disclosure. 
           [0021]      FIG. 10  is a bottom plan view of the auger of  FIG. 2 . 
           [0022]      FIG. 11  is an enlarged partial side plan view of the auger of  FIG. 2 , rotated about 90 degrees from the view of  FIG. 4 . 
           [0023]      FIG. 12  is a cross sectional view of the auger of  FIG. 12 , taken along section lines A-A of  FIG. 11 . 
           [0024]      FIG. 13  is a cross sectional view of the auger of  FIG. 11 , taken along section lines B-B of  FIG. 11 . 
           [0025]      FIG. 14  is a cross-sectional view of the auger of  FIG. 5 , taken along section lines C-C of  FIG. 5   
           [0026]      FIG. 15  is a side plan view of a coupling for the auger according to an embodiment of the present disclosure. 
           [0027]      FIG. 16  is a detail drawing of a flight according to an embodiment of the present disclosure. 
           [0028]      FIG. 17  is a side plan view of a post hole digger showing an auger according to an embodiment of the present disclosure. 
           [0029]      FIG. 18  is a side plan view of the post hole digger of  FIG. 17 , during operation of the auger in digging a hole. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]      FIG. 1  is a side plan view of a post hole digger  5  according to an exemplary embodiment of the present disclosure. The digger  5  is shown installed on a tractor  7  and is used to dig generally-cylindrical holes (not shown) in the ground  8 , for example, holes for fence posts. The digger  5  is disposed at the rear of the tractor  7  between the rear wheels  9  (only one of which is illustrated). 
         [0031]    The digger  5  comprises an auger  10  for drilling into the ground  8 . The auger  10  is supported by a top support arm  6  that extends from the tractor  7  as further discussed herein. A rotating shaft  2  extends from a PTO shaft (not shown) of the tractor  7  and translates rotation from the PTO shaft to a gearbox  4 , and ultimately to the auger  10 . A shield  3  covers moving parts (not shown) that can pose a safety hazard to users (not shown) of the digger  5 . 
         [0032]    The auger  10  comprises a cutting head  12  rigidly mounted to a rotatable shaft  11 . The shaft  11  extends downwardly from the gearbox  4 , which is connected to the tractor&#39;s PTO (not shown) via the rotating shaft  2  in this embodiment. The PTO, rotating shaft  2 , and gearbox  4  translate rotation to the shaft  11 , which turns the cutting head  12 . The shaft  11  comprises a generally hollow tube in the illustrated embodiment. 
         [0033]      FIG. 2  is a bottom perspective view of the auger  10  of  FIG. 1 . The cutting head  12  comprises a blade disc  13  which comprises a plurality of blades  14 . The blades  14  extend from the blade disc  13  downwardly and at an angle such that the rotation of the blade disc  13  causes the blades  14  to dig into soil (not shown) during operation of the auger  10 . The blade disc  13  is a generally flat, generally circular disc with one or more openings  21  along its outer edge  23 . 
         [0034]    An auger tip  15  is removably affixed to the shaft  11  at a lower end of the shaft  11  beneath the cutting head  12 . The auger tip  15  comprises a generally conical extension  17  with one or more blades  16 . The auger tip  15 , conical extension  17  and blades  16  are cast as one piece of material, such as metal, in the illustrated embodiment. The auger tip  15  is removably affixed to the shaft  11  via one or more fasteners  18 . In this regard, the shaft  11  comprises a through hole (not shown) that extends through the shaft  11  generally transverse to the shaft  11 . The auger tip  15  fits into the central opening (not shown) of the shaft  11  and the fastener  18  is inserted through the through hole of the shaft  11  and then through an aligned opening (not shown) that extends transversely through the auger tip. 
         [0035]    The auger  10  further comprises flighting  70  that is rigidly affixed to the shaft  11 . The flighting  70  comprises flights  71  and  72 , each of which extends helically around the shaft, as further defined herein. In the illustrated embodiment, flights  71  and  72  are substantially similar, and are affixed to the shaft  10  by welding, as further discussed herein. The flighting supports the soil (not shown) that is removed from a hole (not shown) during operation of the auger  10 . 
         [0036]      FIG. 3  is a top perspective view of the auger  10  of  FIG. 1 . The blade disc  13  comprises a top surface  24  that is generally flat. The top surface  24  receives soil (not shown) that is removed from the earth (not shown) via the blades  14 . 
         [0037]    The blades  14  are disposed outwardly (in a radial direction) from the shaft  11 . The blades  14  are removably affixed to a mounting bracket  19  that is rigidly affixed to the blade disc  13 . One or more fasteners  20  affix the blades  14  to the mounting bracket  19 . The blades  14  are removable and replaceable when worn or damaged. The illustrated embodiment shows an auger  10  with two (2) blades  14 . Other embodiments of the auger  10  may comprise more or fewer blades  14 . 
         [0038]    In operation of the auger  10 , the shaft  11  rotates in the direction indicated by directional arrow  68 . The blades  14  are oriented facing opposite directions, but both cut (i.e., dig into the soil) in the same direction due to this rotation of the shaft  11 . 
         [0039]    The blades  14  are disposed within the openings  21  ( FIG. 2 ) of the blade disc  13 . In operation of the auger  10  in digging a hole (not shown), shaft  11  rotates, causing the cutting head  12  and auger tip  15  to rotate. The auger tip  15  enters the soil and loosens it with its blade  16 . The blades  14  push soil up onto the top surface  24  of the blade disc. A column (not shown) of soil accumulates on the blade disc  13  until the blade disc  13  is removed from the hole. The flighting  70  supports and lightens the soil and allows a larger column of soil to accumulate than if there were no flighting  70 . 
         [0040]      FIG. 4  is an enlarged partial side view of the auger  10  of  FIG. 1 . In the illustrated embodiment, the mounting bracket  19  comprises a blade mount angle  27  that is rigidly affixed to the blade disc  13 . The blade mount angle  27  comprises an L-shaped section of angle iron welded to the blade disc  13  in one embodiment. 
         [0041]    The mounting bracket  19  further comprises a blade mount bar  26  that is rigidly affixed to the blade mount angle  27 . The blade mount bar  26  comprises a short, generally flat bar that is welded to the blade disc  13  in one embodiment. The blade mount bar  26  comprises one or more openings (not shown) for receiving fasteners  20  for releasably attaching the blades  14  to the mounting bracket  19 . 
         [0042]    The blade  14  is mounted to the blade disc  13  at a downward-sloping angle with its bottom edge  25  facing downward. In the illustrated embodiment, the blade  14  angles downward at an angle of about 45 degrees. In other embodiments, the blade may be differently angled. The blades  14  are affixed to the blade disc  13  within the openings  21  such that bottom edges  25  of the blades  14  extend within the openings  21 . 
         [0043]    The blade  14  comprises an angled blade surface  29 . During operation of the auger  10 , soil (not shown) removed by the blade  14  passes up the blade surface  29  and is deposited onto the top surface  24  of the blade disc  13 . Soil accumulates on the top surface  24  and forms a column of soil (not shown) as the auger  10  digs into the ground (not shown). When the auger  10  is removed from the drilled hole (not shown), the column of soil is removed from the auger by rotating the auger, thus applying centrifugal force to the soil. 
         [0044]    The flights  71  and  72  are rigidly affixed to the shaft  11  at angles to the shaft  11 , as illustrated. The flight  71  is disposed at an angle Θ to the flight  72 . In the illustrated embodiment, the angle Θ is generally 40 degrees. The angle between a horizontal line (indicated by reference line  74 ) and the flights  71  and  72  is Θ/2, as each of the flights  71  and  72  are generally equidistant from the horizontal  74 . 
         [0045]    The flights  71  and  72  move and/or lighten soil as it accumulates on the top surface  24  of the blade disc  13 . In this regard, each flight  71  and  72  comprises a lower end  75   a  and  75   b , respectively and an upper end  76   a  and  76   b , respectively. The soil moves from the lower ends  75   a  and  75   b  upwardly to upper ends  76   a  and  76   b  and continues to accumulate in a column as described herein until the auger  10  is removed from the hole. 
         [0046]    In the illustrated embodiment, the upper ends  76   a  and  76   b  are disposed at substantially the same level as one another, i.e., are disposed in a generally horizontal plane. Similarly, the lower ends  75   a  and  75   b  are disposed in the same generally horizontal plane. 
         [0047]    Outer edges  23  of the disc  13  are generally aligned with an outer edge  73  of the flights  71  and  72 , as indicated by reference lines  79 , in order to form a uniform generally cylindrical hole in operation of the auger. 
         [0048]    In the illustrated embodiment, the auger  10  comprises the two (2) flights  71  and  72 . Other numbers of flights may be used in other embodiments without departing from the scope of the invention. 
         [0049]    Note that the auger tip  15  illustrated in  FIG. 4  has a single helical blade  99  that is different from the plurality of blades  16  illustrated in  FIG. 2 . Any of a number of types of blades may be employed on the auger tip  15  without departing from the scope of the present disclosure. 
         [0050]      FIG. 5  is a top plan view of the auger  10  of  FIG. 2  showing the flighting  70 . Each of the flights  71  and  72  has a generally semi-circular outer edge  73  when viewed from the top as shown. The flights  71  and  72  are “clocked” generally 180 degrees from each other around the shaft  11 . In this regard, the upper ends  76   a ,  76   b  of the flights  71  and  72  are substantially 180 degrees apart, and the lower ends  75   a ,  75   b  of the flights  71  and  72  are substantially 180 degrees apart. 
         [0051]    Further, each of the flights extends generally 180 degrees+“α” around the shaft  11 , where α is the angle that the lower end  75   a  of the flight  71  overlaps the upper end  76   a  of the flight  72 . (Note that α is measured from a reference line  69  tangential to the lower end  75   a  and passing through the center of the shaft  11 .) Similarly, α is also the angle that the lower end  75   b  of the flight  72  overlaps the upper end  76   b  of the flight  71 . Thus each of the flights  71  and  72  extends circumferentially at least 180 degrees around the shaft  11 . However, α is typically less than 90 degrees, and in an exemplary embodiment is substantially 70 degrees. Therefore, the flights  71  and  72  do not extend beyond 270 degrees around the shaft  11  in the exemplary embodiment. In other words, the flighting is distinguishable from “continuous” flighting that extends continuously around a shaft for 360 degrees or more. 
         [0052]      FIG. 6   a  is a front plan view of the blade mount angle  27  of  FIG. 4 . The blade mount angle  27  is rectangular when viewed from the front as illustrated. In one embodiment, the blade mount angle  27  is 3.75 inches wide by 2.5 inches high. 
         [0053]      FIG. 6   b  is a side plan view of the blade mount angle  27  of  FIG. 4 . The blade mount angle  27  is generally L-shaped when viewed from the side as illustrated. In one embodiment, the blade mount angle  27  is 2.5 inches deep and is formed from ⅜ inch thick angle iron. The blade mount angle  27  has a rear surface  36  that is generally flat, a bottom surface  40  that is generally flat, a front surface  38  that is generally flat, and a top surface  39  that is generally flat. The rear surface  36  is generally perpendicular to the bottom surface  40  and forms an “L” shape in conjunction therewith. The front surface  38  is generally perpendicular to the top surface  39  and forms a general “L” shape in conjunction therewith. 
         [0054]      FIG. 7   a  is a front plan view of the blade mount bar  26  of  FIG. 4 . The blade mount bar  26  is a generally flat, generally rectangular bar, and in one embodiment is 2.5 inches high by 3.75 inches wide, and is formed from ⅜ inch steel. The blade mount bar  26  comprises one or more openings  37 , which openings  37  receive the fasteners  20  ( FIG. 4 ) for removably affixing the blade  14  ( FIG. 4 ) to the blade mount bar  26 . 
         [0055]      FIG. 7   b  is a side plan view of the blade mount bar  26  of  FIG. 4 . The blade mount bar  26  comprises a front side  44  that is generally flat. The blade mount bar  26  further comprises a rear side  43  and top and bottom sides  45  and  46 , respectively. The top side  45  forms a corner  41  in conjunction with the rear side  43 . The bottom side  46  forms a corner  42  in conjunction with the rear side  43 . 
         [0056]      FIG. 8   a  is a top plan view of the blade  14  of  FIG. 4 . One embodiment of the blade  14  is somewhat rectangular in shape, with a top generally straight side  48  that is generally parallel to the bottom edge  25 . A generally straight right side  49  is generally perpendicular to and extends between the top side  48  and the bottom edge  25 . A left side  51  comprises straight portions  58  and  57  that join together via a curved portion  59 . The straight portions  58  and  57  are generally parallel to the right side  49 . Further, the straight portion  58  is spaced apart from the straight portion  57 , such that the bottom portion of the blade  14  is wider than the top portion of the blade, i.e., the distance between right side  49  and portion  58  is greater than the distance between the right side  49  and the portion  57 . In the illustrated embodiment, the blade  14  is about 4.5 inches wide by 4.25 inches tall, and is formed from V 2  inch thick steel. 
         [0057]    The blade  14  further comprises a plurality of openings  47  that extend through the blade  14 . The openings  47  receive the fasteners  20  ( FIG. 4 ) that removably affix the blade  14  to the blade mount bar  26  ( FIG. 4 ). The openings  47  are countersunk in the illustrated embodiment. 
         [0058]      FIG. 8   b  is a side plan view of the blade  14  of  FIG. 4 . The blade  14  comprises a generally flat top side  54  and a generally flat bottom side  53 . The top side  54  is generally parallel to the bottom side  53 . An angled blade portion  55  extends from the bottom side  53  to the top side  54  and terminates in a sharp bottom edge  25  at the bottom tip of the blade  14 . 
         [0059]      FIG. 8   c  is a front plan view of an alternative embodiment of a blade  140 . In this embodiment, the blade  140  is trapezoidal in shape, with a top side  148  and bottom edge  125  substantially parallel to each other, and a right side  149  and a left side  151  at an angle to each other that is greater than zero. In this embodiment, there are no offset portions  57  and  58  ( FIG. 8   a ), such that side the left side  151  is a generally straight line that is a mirror image of the right side  149 . Further, this embodiment of the blade  140  is formed from  1 / 2  inch thick steel. 
         [0060]      FIG. 9  is bottom plan view of a blade disc  13  according to an exemplary embodiment of the present disclosure. In this embodiment, the blade disc  13  has two curved edges  31  that are partially circular. In this regard, the blade disc  13  is partially circular with irregularly-shaped openings  21   a  and  21   b  in two places along its outer, circular edge  23 . (The circular edge  23  is shown in broken lines where material has been removed to create the openings  21   a  and  21   b .) In one embodiment, the blade disc  13  is formed from a  12  inch diameter circular steel plate that is ⅜″ thick. 
         [0061]    The two openings  21   a  and  21   b  are substantially similar and are disposed 180 degrees apart on the blade disc  13  in the illustrated embodiment. Other embodiments may utilize more or fewer openings  21   a  and  21   b , and the openings  21   a  and  21   b  may be differently spaced. 
         [0062]    The opening  21   b  comprises a straight wall  32  that is generally parallel to the y-axis of  FIG. 8 . A straight wall segment  33  is generally perpendicular to the straight wall  32 . The blade mount angle  27  ( FIG. 4 ) is rigidly affixed to the wall  32 . In this regard, the rear surface  36  ( FIG. 5   b ) of the blade mount angle  27  is welded to the wall  32 . 
         [0063]    The opening  21   b  further comprises a radial wall  34  that in the illustrated embodiment is aligned radially with the center of the blade disc  13  at an angle of 45 degrees from the wall  32 . A short curved wall segment  35  extends between the straight wall segment  33  and the radial wall  34 . 
         [0064]    The blade disc  13  comprises a central opening  30  centrally located on the blade disc  13 . The central opening  30  receives the shaft  11 , thus is slightly larger than the shaft  11 . The central opening is 2 and 17/32 inches in diameter in one embodiment, but may be sized differently in other embodiments. In the illustrated embodiment, the shaft  11  is affixed to the blade disc  13  by welding. 
         [0065]      FIG. 10  is a bottom plan view of the auger  10  of  FIG. 1 . The fastener  18  passes through the opening (not shown) in the auger tip  15  and the opening (not shown) in the shaft  11  and releasably attaches the auger tip  15  to the shaft  11 . 
         [0066]    The rear surface  36  of the blade mount angle  27  is rigidly affixed to the straight wall  32  of the blade disc  13 , such that the blade  14  extends into the opening  21   b . Further, the straight portion  58  of the left side  51  ( FIG. 8   a ) of the blade  14  extends towards the auger tip  15 . Note that the blades  16  extend outwardly of the left side  51  of the blade  14  such that there is no “gap” between the blades  16  of the auger tip  15  and the blades  14 , in this embodiment. 
         [0067]      FIG. 11  is an enlarged partial side plan view of the auger  10  of  FIG. 4 , rotated about 90 degrees from the view of  FIG. 4 . The fastener  18  releasably affixes the auger tip  15  to the shaft  11 . The fastener may be any type of standard fastener, such as a threaded bolt coupleable with a threaded nut. 
         [0068]    In one embodiment the flighting  70  is spaced apart from the blade disc  13  by about 8 inches, though other distances may be used in other embodiments. 
         [0069]      FIG. 12  is a cross-sectional view of the auger  10  of  FIG. 11 , taken along section lines A-A of  FIG. 11 . The blades  14   a  and  14   b  are substantially similar and face in opposite directions as shown. The blades  14   a  and  14   b  are disposed within the openings  21   a  and  21   b  of the blade disc  13 . A plurality of fasteners  20  releasably attaches the blades  14   a  and  14   b  to the mounting brackets  19   a  and  19   b.    
         [0070]      FIG. 13  is a cross-sectional view of the auger  10  of  FIG. 11 , taken along section lines B-B of  FIG. 11 . The lower ends  75   a  and  75   b  of the flights  71  and  72 , respectively, are clocked generally 180 degrees from one another with respect to the shaft  11 . 
         [0071]      FIG. 14  is a cross-sectional view of the auger of  FIG. 5 , taken along section lines C-C of  FIG. 5 . (The cutting blades  14  and the auger tip  15  are not included in this cross-sectional view.) A coupling  19  is received by and rigidly affixed to an upper end  80  of the shaft  11 . In this regard, the shaft  11  is generally cylindrical and generally hollow and the coupling  19  is generally cylindrical and generally hollow. An outer diameter of the coupling  19  is smaller than the inner diameter of the shaft  11  such that the coupling  19  fits within the shaft  11 . The coupling  19  is affixed to the shaft  11  by welding in the illustrated embodiment. 
         [0072]      FIG. 15  is an enlarged side plan view of the coupling  80  of  FIG. 14 . The coupling  80  comprises a body  91  with cylindrical walls that fit within the shaft  11  ( FIG. 14 ) as discussed above. The coupling  80  further comprises a shoulder  88  on its upper end. The shoulder  88  is larger in diameter than the body  91  and fits against the upper end  80  ( FIG. 14 ) of the shaft  11 . Female threads  87  inside the coupling  80  mate with male threads (not shown) on a shaft (not shown) on the gearbox  4  ( FIG. 1 ). The shoulder  88  is generally smooth and generally cylindrical with no protrusions that the user (not shown) could get caught on in use of the auger  10  ( FIG. 1 ). The coupling  80  comprises a chamfered edge  89  which transitions to a top surface  92  of the coupling  80 . 
         [0073]      FIG. 16  is a front plan view of the flight  71  of  FIG. 2  before the flight  71  is rigidly affixed to the shaft  11  ( FIG. 1 ). The flight  71  has an outer edge  73  that curves smoothly from an upper end  76   a  to a lower end  75   a . The upper end  76   a  comprises a corner  84  that is coextensive with a generally straight trailing edge  93 . The trailing edge  93  extends radially from the shaft  11 , when the flight  71  is affixed to the shaft  11 . The trailing edge  93  extends between the corner  84  and a curved corner  83  that transitions smoothly to a large curve  85  that extends at least 180 degrees and transitions to a smaller curve at the lower end  75   a  before terminating at a corner  86 . 
         [0074]    The corners  84  and  86  are adjacent to the shaft  11  when the flight  71  is installed on the shaft  11 . An inner surface  82  is semi-circular to conform to an outer surface (not shown) of the shaft  11 . A generally semi-circular central opening  81  in the flight  71  is defined by the inner surface  82  and the corners  84  and  86 . The opening  81  receives the shaft  11  when the flight  71  is affixed to the shaft  11 . 
         [0075]    The flight  72  is substantially similar to the flight  71 . The flights  71  and  72  are both formed from a generally flat plate of 10 gauge steel in the illustrated embodiment, though other materials and sizes may be used in other embodiments. The flights  71  and  72  are rigidly affixed to the shaft  11  ( FIG. 1 ) by welding in the illustrated embodiment. 
         [0076]      FIG. 17  is a side plan view of a post hole digger  50  according to an embodiment of the present disclosure, before the auger  10  begins digging into the ground  8 . The length of the auger  10  in this embodiment is “Ls,” and the distance above the flighting  70  is “Lt.” Importantly, the shaft  11  above the flighting  70  is substantially free of protrusions that can potentially harm a user (not shown) in operation of the auger  10 . 
         [0077]    In an exemplary embodiment, Ls is approximately 39 inches and Lt is approximately 26 and 13/16 inches. The ratio of Lt to Ls, or Lt/Ls, is 0.6875. Ideally the ratio of Lt/Ls should be ⅔ or greater, to provide a shaft that is substantially free from protrusions. 
         [0078]      FIG. 18  is a side plan view of the post hole digger  50  of  FIG. 17  while the auger  10  is digging a hole  170 . (The soil removed from the hole  170  is not illustrated.) There are no extensions or protrusions between the gearbox  4  and the flighting that the user can get caught on. Therefore, once the flighting  70  is beneath the soil  8 , the user is safe from that risk.

Summary:
An auger for digging holes in soil is coupled to a gearbox and powered by the power take-off of a tractor. The auger comprises a shaft with a cutting head disposed near its bottom end. The cutting head comprises a plurality of cutting (i.e. digging) blades that cut into soil. Flighting disposed above the cutting head moves and lightens soil, but the flighting does not extend far above the cutting head. The majority of the shaft is free from protrusions that may ensnare a user of the auger during use.