Patent Publication Number: US-9834999-B2

Title: Post hole digger

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application 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 incorporated herein by reference. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     A post hole digger attaches to the standard three point hitch of the tractor and is powered by the tractor&#39;s power take-off (PTO). The digger comprises an auger without protrusions or other extending parts above the fighting of the auger, to reduce the possibility of a user becoming ensnared during use of the digger. A shield covering rotating parts of the PTO shaft is rigidly affixed to the support arm that supports the auger. 
     In one embodiment, the shield is rigidly affixed to the gearbox that translates rotation from the PTO shaft to the auger. The shield therefore moves with the gearbox as the auger is adjusted, maintaining a uniform cover over the rotating parts of the PTO shaft and protecting users. In another embodiment, the shield is rotatably affixed to the gearbox and is sized to provide appropriate coverage regardless of the position of the auger in use. 
     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 
       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. 
         FIG. 1  is a side plan view of a post hole digger according to an embodiment of the present disclosure coupled to a tractor. 
         FIG. 2  is a rear perspective view of the post hole digger of  FIG. 1 . 
         FIG. 3  is an enlarged side plan view of the post hole digger of  FIG. 1 . 
         FIG. 4  is a side plan view of the post hole digger of  FIG. 3 , with hidden lines included to show detail hidden by the shield. 
         FIG. 5  is a rear plan view of the post hole digger of  FIG. 1 . 
         FIG. 6  is an enlarged detail view of the digger of  FIG. 5 , taken along detail line A of  FIG. 5 . 
         FIG. 7  is a rear perspective view of a post hole digger according to an embodiment of the present disclosure. 
         FIG. 8  is an enlarged perspective view of a shield according to an embodiment of the present disclosure. 
         FIG. 9  is a side plan view of the shield of  FIG. 8 . 
         FIG. 10  is an enlarged detail view of the shield of  FIG. 9 , with hidden lines showing components hidden in  FIG. 9 . 
         FIG. 11  is a cross-sectional view of the shield of  FIG. 10 , taken along section lines B-B of  FIG. 10 . 
         FIG. 12  is a side plan view of the digger of  FIG. 7 . 
         FIG. 13  is a is a side plan view of the digger of  FIG. 12 , after the digger has begun digging a hole. 
         FIG. 14  is a side plan view of the digger of  FIG. 12 , with the auger extended rearwardly to expose the clutch and cross and bearing joint for maintenance. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a side plan view of a post hole digger  10  according to an exemplary embodiment of the present disclosure. The digger  10  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  10  is disposed at the rear of the tractor  7  between the rear wheels  9   a  and  9   b  ( FIG. 2 ). 
     The digger  10  comprises an auger  13  for drilling into the ground  8 . The auger  13  is supported by a top support arm  18  that extends from the tractor  7  as further discussed herein. A rotating shaft  17  extends from a PTO shaft (not shown) of the tractor  7  and translates rotation from the PTO shaft to a gearbox  12 , and ultimately to the auger  13 . A shield  19  covers moving parts (not shown) that can pose a safety hazard to users (not shown) of the digger  10 . 
       FIG. 2  is a rear perspective view of the digger  10  installed on the tractor  7  between the wheels  9   a  and  9   b  of the tractor  7 . The digger  10  connects to the tractor&#39;s standard three point hitch that is known in the art. The term “three point hitch” refers to the three mounting points of a tractor hitch that extend rearwardly from the rear of the tractor  7 . The three point hitch comprises a topmost point  21 , a right lift arm  11   a  and a left lift arm  11   b . The topmost point  21  of the three point hitch connects to the top support arm  18 . Specifically, the top support arm  18  comprises a generally straight segment  22  and a generally curved segment  23 . The straight segment  22  is releasably affixed to the topmost point  21  of the three point hitch. The right and left lift arms  11   a  and  11   b  releasably affix to a support frame  24  that supports the support arm  18 . 
     In this embodiment, the support frame  24  comprises a curved frame generally shaped as an inverted “U.” A lower right end  25  of the support frame  24  rotatably connects to the right lift arm  11   a  via a pin  43  that passes through an opening (not shown) of the right lift arm  11   a . A lower left end  26  of the support frame  24  rotatably connects to the left lift arm  11   b  via a pin  44  that passes through an opening of the left lift arm  11   b . The support frame  24  is thus rotatable with respect to the lift arms  11   a  and  11   b.    
     The inverted “U” shape of the support frame  24  allows the frame  24  to support the support arm  18  without interfering with the operation of the rotating shaft  17 . In other words, the rotating shaft  17  is free to rotate, and otherwise move within, the open space  79  within the inverted “U” shape of the support frame  24 . By way of example only, if the support frame  24  extended directly between the right and left lift arms  11   a  and  11   b  and then upwardly, instead of arching upward as illustrated, the support frame  24  might interfere with the operation of the rotating shaft  17 . 
     At its upper end, the support frame  24  comprises a pair of brackets  27  and  28  that rotatably affix to the straight segment  22  of the support arm  18 . In this regard, openings (not shown) in the straight segment  22  receive a fastener  38  rotatably connecting the brackets  27  and  28  to the straight segment  22 . 
     The support arm  18  extends upwardly and rearwardly from the tractor  7 . The straight segment  22  and the curved segment  23  of the support arm  18  are comprised of hollow metal tubing in the illustrated embodiment. Although the metal tubing comprising the curved segment  23  and the straight segment  22  is shown as round tubing in  FIG. 2 , tubing with a square or rectangular cross section is employed in other embodiments. The curved segment  23  of the support arm curves downwardly from a rearward end of the straight segment  22  to the shield  19 . 
     The curved segment  23  is rotatably affixed to the shield  19 . In this regard, top shield brackets  29   a  and  29   b  are rigidly affixed to the shield  19 . The top shield brackets  29   a  and  29   b  comprise openings (not shown) which receive a pin  68  which extends through the bracket  29   b , through an opening (not shown) in the curved segment  23 , and through the bracket  29   b . The pin  28  is secured with a pair of hairpin retainers  69  (only one of which is shown in  FIG. 2 ). The top shield brackets  29   a  and  29   b  are rigidly affixed to the shield  19  by welding in this embodiment, though other means of rigidly affixing the top shield brackets  29   a  and  29   b  to the shield  19  may be utilized in other embodiments. Further, other means of rotatably connecting the shield  19  to the support arm  18  may be utilized in other embodiments. 
     The shield  19  is formed from generally thin rigid material and is metallic in the illustrated embodiment. The shield  19  is formed as a generally inverted “U” shape when viewed from the rear of the digger  10 , and is comprised of a top segment  163 , a downwardly-extending right segment  171 , and a downwardly-extending left segment  172 . In the illustrated embodiment, the top segment  163 , right segment  171 , and left segment  172  of the shield  19  are formed from bending a unitary flat piece of metal. 
     The shield  19  is rigidly affixed to the gearbox  12 , via fasteners  37  in this embodiment, though other means of rigidly affixing the shield to the gearbox may be utilized in other embodiments. The shield  19  is not detachable from the digger in this embodiment without making the digger non-functional, to provide safety for the user. 
     The rotating shaft  17  is releasably coupled to a PTO shaft  20  of the tractor  7 . As known by persons of skill in the art, a power-take off shaft is a splined shaft that is rotatable by the user (not shown) upon actuation of the tractor controls (not shown). Rotation of the PTO shaft  20  typically powers farming implements such as the digger  10 . The rotating shaft  17  extends from the PTO shaft  20  to the gearbox  12 , as further discussed herein. The rotating shaft  17  is comprised of hollow tubing in the illustrated embodiment. 
     The shaft  17  telescopes (i.e., becomes longer or shorter) as required during the operation of the digger  10 . In this regard, a frontward segment  31  of the rotating shaft  17  is extendably coupled to a rearward segment  32  of the rotating shaft. An outer diameter of the rearward segment  32  is larger than an inner diameter of the frontward segment  31  such that the rearward segment  32  is received by and extendably slides within the frontward segment  31 . 
     The gearbox  12  receives rotation from the rotating shaft  17  and translates the received rotation to the auger  13 . In this embodiment, the auger  13  comprises a rotatable auger shaft  33 , fighting blades  14  and a cutting head  15 . The cutting head  15  is disposed at the lowermost end of the shaft  33 , and comprises a pilot bit  16  and a pair of cutting blades  34 . The fighting blades  14  are disposed above the cutting head  15 . 
     The shaft  33  is formed from generally cylindrical hollow tubing in the illustrated embodiment. The outer surface of the shaft  33  is generally smooth above the fighting blades  14 , and has no protrusions or other irregularities above the fighting blades  14  that may ensnare or entangle a user during use. 
       FIG. 3  is an enlarged side plan view of the digger  10  of  FIG. 1 . The right segment  171  of the shield  19  extends downwardly from the top segment  163 . The right segment  171  comprises a front edge  165  that extends downwardly from the top segment  163 , a rear edge  166  that extends downwardly from the top segment  163 , and a bottom edge  164 . Chamfers  167  and  168  at the intersections of the front edge  165  with the bottom edge  164  and the rear edge  166  with the bottom edge  164  eliminate sharp corners from the shield  19 . Although not illustrated in  FIG. 3 , the left segment  172  ( FIG. 2 ) is substantially similar to, and a mirror image of, the right segment  171 . 
       FIG. 4  is a side plan view of the digger  10  of  FIG. 3 , with hidden lines included to show detail hidden by the shield  19  and tractor  7 . As discussed above, the rotating shaft  17  receives rotation from the PTO shaft  20  and translates that rotation to the gearbox  12 . The rotating shaft  17  extends upwardly and at an angle from the PTO shaft  20  and terminates at a cross and bearing joint  35 . The cross and bearing joint  35  translates rotation from the rotating shaft  17  to a slip clutch  36 . The slip clutch  36  is a friction clutch that will slip when the torque from the rotating shaft  17  becomes too great, for example, if the auger  13  stops turning due to an obstruction. The slip clutch  36  minimizes the possibility of damage to the digger  10  in this event. Prior art diggers typically use shear bolts (not shown) that are known in the art to protect against such damage. A shear bolt is an intentionally-weakened part that will break if the auger  13  stops turning or becomes entangled. A disadvantage of shear bolts is that they must be replaced after they break. The slip clutch  36  is a more durable solution. 
     The slip clutch  36  is rigidly affixed to a gearbox shaft  42  that extends frontwardly from the gearbox  12 . The slip clutch  36  and the gearbox shaft  42  both rotate upon receipt of rotation from the rotating shaft  17 . 
     The shield  19  covers the joint  35  and clutch  36  and gearbox shaft  42  to minimize the possibility of a user becoming entangled in the moving parts in the vicinity of the joint  35 . Because the shield  19  is rigidly affixed to the gearbox  12 , the shield covers the joint  35  regardless of the position of the digger  10  (i.e., regardless of whether the digger is lowered or raised during digging of a hole). 
     The top support arm  18  rotates in a generally vertical plane with respect to the tractor  7  around point  40 . The top support arm  18  is rotatably affixed to the shield  19  via the top shield bracket  29   b  and pin  68 . The support frame  24  is rotatable around the pin  43  and also around the fastener  38  (at the bracket  28 ). 
       FIG. 5  is a rear plan view of the digger  10  of  FIG. 1 . As was discussed above, the lower right end  25  of the support frame  24  rotatably connects to the right lift arm  11   a  via the pin  43  that passes through the lower right end  25  and through the right lift arm  11   a . The lower left end  26  of the support frame  24  rotatably connects to the left lift arm  11   b  via the pin  44  that passes through an opening of the left lift arm  11   b . The support frame  24  is thus rotatable with respect to the lift arms  11   a  and  11   b  at pins  43  and  44 . 
     The support frame  24  is in the general shape of an inverted “U,” and this shape allows the frame  24  to support the support arm  18 , using the right and left lift arms  11   a  and  11   b , without interfering with the operation of the rotating shaft  17 . 
     The support frame  24  extends upwardly and inwardly from the right lift arm  11   a  and extends upwardly and inwardly from the left lift arm  11   b . The support arm  18  is located generally centrally with respect to the support frame  24 , as illustrated. 
       FIG. 6  is an enlarged detail view of the digger  10  of  FIG. 5 , taken along detail line “A” of  FIG. 5 . The shield bracket  29   a  comprises an upwardly-extending portion  88  that comprises an opening (not shown) for receiving the pin  68 . The shield bracket  29   a  further comprises a bottom portion  87  that is rigidly affixed to the top segment  163  of the shield  19 , by welding in the illustrated embodiment. The shield bracket  29   b  is substantially similar to, and a mirror image of, the bracket  29   a . The curved segment  23  at its rearward end comprises a sleeve bracket  181  that receives the pin  68 . The pin thus passes through the shield bracket  29   a , the sleeve bracket  181 , and the shield bracket  29   b , in order to rotatably couple the curved portion  23  of the top support arm  18  ( FIG. 5 ) to the shield  19 . The hairpin retainers  69  retain the pin  68  within the brackets  29   a ,  181 , and  29   b.    
     The gearbox  12  comprises a top gearbox cover  179  that is rigidly affixed to the gearbox  12  via a plurality of fasteners  180 . The gearbox cover  179  is further rigidly affixed to the shield  19  via a plurality of fasteners  37 . In this manner, the shield  19  is rigidly affixed to the gearbox  12 , and cannot be removed from the gearbox  12  without rendering the digger  10  ( FIG. 5 ) inoperable. 
       FIG. 7  is a rear perspective view of a post hole digger  100  according to an alternative embodiment of the present disclosure. The post hole digger  100  comprises the substantially similar rotating shaft  17 , gearbox  12 , and auger  13  as the post hole digger  10  of  FIG. 2 . In this embodiment, a shield  119  covers the rotating parts (not shown) of the digger  100 . However, the shield  119  is not rigidly affixed to the gearbox  12  in this embodiment. Rather, the shield  119  is rigidly affixed to the top support arm  118 , and the gearbox  12  is rotatably affixed to the top support arm  118 , such that the gearbox  12  rotates with respect to the top support arm  118  along an axis (not shown) passing through openings  101  of the shield, as further discussed below. 
     The top support arm  118  extends from and is rotatably coupled to the topmost point  21  of the three point hitch of the tractor  7  and supports the gearbox  12  and auger  13 . A support frame  124  extends between and is rotatably affixed to the right lift arm  11   a  and left lift arm  11   b . The support frame  124  extends up to and rotatably couples with the top support arm  118 . In this manner the support frame  124  rotatably supports the top support arm  118 . 
     The support frame  124  is generally in the shape of an inverted “U” with a right segment  125  extending upwardly and at an angle from the right lift arm  11   a , a left segment  126  extending upwardly and at an angle from the left lift arm  11   b , and a connecting segment  107  extending between the right segment  125  and the left segment  126 . The connecting segment  107  is generally straight and generally horizontal in the illustrated embodiment. A pair of brackets  128  (only one of which is shown in  FIG. 7 ) extends upwardly from the connecting segment  107  and rotatably affixes the connecting segment  107  to the top support arm  118  via a pin  127  that extends through the top support arm  118 . 
     The inverted “U” shape of the support frame  124  allows the frame  124  to support the support arm  118  without interfering with the operation of the rotating shaft  17 . In other words, the rotating shaft  17  is free to rotate, and otherwise move within, the open space  79  within the inverted “U” shape of the support frame  124 . By way of example only, if the support frame  124  extended directly between the right and left lift arms  11   a  and  11   b  and then upwardly, instead of arching upward as illustrated, the support frame  124  might interfere with the operation of the rotating shaft  17 . 
       FIG. 8  is an enlarged perspective view of the shield  119  of  FIG. 7 . The shield  119  is a generally thin, metal shield that is fabricated from bent steel in one embodiment. A flat top portion  150 , a downwardly-extending right portion  151 , and a downwardly-extending left portion  152  form the general shape of an inverted “U” when the shield  119  is viewed from the rear. The flat top portion  150  is in a generally trapezoidal shape with a narrow forward edge  160  that is rigidly affixed to the top support arm  118 , by welding in the illustrated embodiment. In this regard, the top support arm  118  comprises generally hollow rectangular tubing and the forward edge  160  of the top portion  150  of the shield  119  narrows to generally the same width as the top support arm  118  and is affixed thereto. A rearward open edge  161  of the flat top portion  150  widens to a width greater than the width of the gearbox  12 . Frontward side portions  162  (only one of which is shown in  FIG. 8 ) are rigidly affixed to sides of the top support arm  118 , by welding in the illustrated embodiment. 
     The flat top portion  150  extends transversely along the top support arm  118  such that the moving parts (e.g., the joint  35  ( FIG. 10 ) and the shaft  42  ( FIG. 10 ) of the digger  100  are covered on a top side of the digger  100 . 
       FIG. 9  is a side plan view of the shield  119  of  FIG. 8 . The right portion  151  of the shield  119  comprises a rearward edge  159  that extends downwardly from the rearward open edge  161  ( FIG. 8 ) to a curving corner  158 . The curving corner  158  transitions to an angled portion  157  that terminates at a lowermost corner  156 . An angled frontward side  155  extends from the lowermost corner  156  up to the frontward side portion  162 . Note that the corners  158  and  156  are rounded such that the shield  119  is generally free of sharp corners. Although not illustrated in  FIG. 9 , the left portion  152  ( FIG. 8 ) of the shield is substantially similar to, and a mirror image of, the right portion  151 . In the illustrated embodiment, the shield  119  does not extend to completely cover the gearbox  12 . However, this is not problematic because there are generally no moving parts at the rear of the gearbox  12  and the exposed portion of the auger shaft  33  is generally free from protrusions that can ensnare the user. A key feature is that the right portion  151  (and similarly, the left portion  152  ( FIG. 8 )) extends sufficiently downwardly and is sufficiently wide such that the moving parts (e.g., the joint  35  ( FIG. 10 ) and the shaft  42  ( FIG. 10 ) are covered on opposed sides of the digger  100  while the digger  100  is in operation. 
       FIG. 10  is an enlarged side plan view of the portion of the digger  10  shown in  FIG. 9 , including hidden lines to illustrate the components hidden by the shield  119 . The cross and bearing joint  35 , the clutch  36 , and the gearbox shaft  42  are fully covered by the shield  119  in this embodiment to protect the user from ensnarement. 
     The shield  119  is rigidly affixed to angles  183  and  184  ( FIG. 11 ), by welding in the illustrated embodiment. The angles  183  and  184  are rigidly affixed to the top support aria  118 , by welding in the illustrated embodiment. Further, the angles  183  and  184  are rotatably affixed to the top gearbox cover  279 , as further discussed below with respect to  FIG. 11 . The top gearbox cover  279  is rigidly affixed to the gearbox  12  via a plurality of fasteners  180 . In this manner the shield  119  is rotatably coupled to the gearbox  12  such that the shield  119  may not be removed by the user without rendering the digger  10  ( FIG. 7 ) inoperable. 
       FIG. 11  is a cross-sectional view of the shield  119  of  FIG. 10 , taken along section lines B-B of  FIG. 10 . Angles  183  and  184  are comprised from angle iron and are welded to the shield  119  in the illustrated embodiment. The gearbox cover  279  comprises brackets  129   a  and  129   b  that are rigidly affixed to the gearbox cover  279  and comprise openings (not shown) for receiving a pin  185  that rotatably couples the angles  183  and  184  to the gearbox cover  279 . In this regard, the angles  183  and  184  comprise openings (not shown) for receiving the pin  185 . The pin  185  thus is received by and extends through the bracket  129   a , the angle  184 , the angle  183 , and the bracket  129   b . Openings  101  on either side of the shield  119  align with the pin  185  and are for tooling purposes. 
       FIG. 12  is a side plan view of the post hole digger  100  of  FIG. 7 , before the auger  13  begins digging into the ground  6 . Note that in this position, the top support arm  118  is generally parallel to the rotating shaft  17 , in this embodiment. Further, the shield  119  fully covers the rotating parts (e.g., the joint  35  ( FIG. 10 ), the shaft  42  ( FIG. 10 ), and the clutch  36  ( FIG. 10 )) that are most likely to be injurious to the user (not shown). 
       FIG. 13  is a side plan view of the post hole digger  100  of  FIG. 12  after the auger  13  has begun digging a hole  170 . During hole-digging operation, the auger  13  is typically in a generally-vertical orientation (for a hole that is desired to be generally vertical). As the auger  13  digs, the support arm  118  and shield  119  rotate with respect to the gearbox  12  around pin  185 . Further, the angle between the top support arm  118  and the shield  119  widens such that the joint  35  ( FIG. 10 ) is further from the top support arm  118 . The shield  119  is sized such that the downwardly-extending right portion  151 , and the downwardly-extending left portion  152  ( FIG. 8 ) extend sufficiently to keep opposed sides (not shown) of the joint  35  covered even when the auger  13  is deployed at its lowest point. This arrangement prevents the joint  35  and other potentially dangerous rotating parts forward of the gearbox  12  from being exposed to the user during use of the auger. 
       FIG. 14  is a side plan view of the digger  100  of  FIG. 13 , with the auger  13  extended rearwardly at an angle. The auger  13  would not normally be extended in this manner during use of the digger  100 , but such a position would be desired by the user during maintenance of the digger  100 , for example. Extension of the auger  13  as illustrated exposes the joint  35  and the clutch  36 , which are then accessible by the user for maintenance. The shield  119  is thus designed so that the most dangerous rotating parts of the digger  100  (such as the clutch  36  and joint  35 ) remain shielded during operation of the digger and are accessible for maintenance.