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BACKGROUND OF THE INVENTION 
     A. Field of the Invention 
     The present invention relates to tools and implements for making elongated circular cross-section bore holes such as post holes into soil beneath the surface of the ground. More particularly, the invention relates to a hole digger tool and apparatus which uses a vacuum pump to remove soils severed by cutting teeth and has a rotating unclogger bar to break up mud or clay clogs which could impede removal of dislodged soil. 
     B. Description of Background Art 
     There are a variety of situations which require making elongated, relatively deep holes into the ground. These include digging generally cylindrically-shaped holes for receiving fence posts, sign posts and the like. Such holes have a typical diameter range of from about 4 inches to about 12 inches, and a depth of 3 to 6 feet or more. 
     Digging relatively deep, elongated holes such as post holes in the ground tends to be a tedious, slow, labor intensive task, when using conventional manually operated, manually powered digging implements. A widely used manually powered, “clam-shell” post hole digger includes a pair of shovels, each of which has a generally semi-circularly curved blade. The shovel blades are fixed to the lower ends of upwardly protruding handles which are pivotably mounted to one another at a location between the shovel blades and the upper ends of the handles, and arranged so that the concave surfaces of the shovel blades confront one another to define therebetween a generally cylindrically-shaped space corresponding to a hole to be dug. 
     Clam-shell post hole diggers are used by pivoting the upper ends of the handles towards one another to place the handles in generally parallel alignment with one another, thus also orienting the shovel blades at the lower ends of the handles in generally parallel alignment. The handles are then grasped by an operator to orient them vertically, i.e., perpendicularly to a ground surface into which a post hole is to be dug. The operator then brings his arms down forcefully towards the surface of the ground, thus causing pointed tips of the shovel blades to penetrate the ground soil, and the handles are rocked back and forth in a horizontal direction, to thus impart a twisting cutting motion to the shovel blades. 
     Next, the upper ends of the handles are drawn apart to thus pivot the shovel blades towards one another, underneath soil which has been loosened by downward and twisting cutting actions of the shovel blades. The claim-shell digger tool is then raised above the ground to thus withdraw the shovel blades from the ground and thereby remove the severed soil, which may then be dumped at any convenient location. This is done by pushing the upper ends of the handles together, thus causing the inner facing concave surfaces of the shovel blades to pivot away from one another, allowing soil supported on those surfaces to fall away from the blades. 
     The handles are once again put into parallel alignment, and claim-shell digger tool is again thrust downward to thus drive the shovel blades downward into the hole being dug to thereby begin a new cycle of soil excavating. These cycles are repeated as often as required to dig a hole of a desired depth. As can be well appreciated, digging post holes with a clam-shell digging tool of this type is a very laborious, slow task. 
     Another method of forming post holes which is in common use employs a large diameter auger that is rotated by an electric, hydraulic or air-driven motor. Boring post holes with a powered auger of this type is much quicker and easier than using a claim-shell type digger tool, but the cost of such devices, and the requirement of providing electric, hydraulic or compressed air power to them, limits the extent of their use. 
     In apparent recognition of certain limitations of clam-shell or auger-type post hole diggers, U.S. Pat. No. 7,185,720 disclosed a hole digger which includes an elongated, skeletonized cylinder that has circumferentially spaced apart, elongated bars which are fastened at the upper ends thereof to the periphery of an upper mounting ring, and near the lower ends of the bars to a lower, mounting ring. The bars extend below the lower mounting ring and terminate in wedge-shaped, pointed cutting teeth. 
     The digging tool disclosed in U.S. Pat. No. 7,185,720 includes a straight, hollow vacuum tube which fits coaxially down through the bore of the skeletonized frame and is longitudinally movable therewithin. The upper end of the vacuum tube is connected through a flexible vacuum hose to a vacuum source, such as a wet-or-dry shop vacuum unit. The tool is used by pressing the pointed edges of the cutting teeth into a soil surface, twisting the unit back and forth with respect to its longitudinal axis to thus cause the teeth to exert a rotary cutting action on the soil surface, and oscillating the vacuum tube up and down to thus vacuum up severed soil. 
     While the hole digger implement disclosed in U.S. Pat. No. 7,185,720 appears to be an improvement over certain prior art hole diggers such as clam-shell type hole diggers, the present inventor has found that diggers of the type disclosed in the &#39;720 patent have certain limitations. For example, the requirement that the vacuum tube in the &#39;720 digger be oscillated up and down can become burdensome. Also, the present inventor has found that using vacuum assisted hole diggers of the type described in U.S. Pat. No. 7,185,720 in wet, muddy or clay soil can be problematic, because the mud or clay tends to lodge within the vacuum tube, thus clogging the bore of the vacuum tube and preventing soil from being drawn upwardly through the tube. 
     The foregoing considerations in part prompted the present invention, which is described in detail below. 
     OBJECTS OF THE INVENTION 
     An object of the present invention is to provide a vacuum assisted post hole digger apparatus for boring post holes in soil which includes a vacuum assisted post hole boring tool and a vacuum source. 
     Another object of the invention is to provide a vacuum assisted post hole digger tool which includes an elongated hollow tubular housing that has a vacuum inlet fitting at an upper end thereof and a plurality of circumferentially spaced apart soil cutting blades or teeth which are attached to the outer circumferential surface of a cylindrical sleeve located at the lower end of the tubular housing, the cutting teeth extending below the lower transverse annular end wall of the sleeve. 
     Another object of the invention is to provide a vacuum assisted post hole digger tool which includes an elongated zig-zag shaped mud and clay unclogger bar that is attached at an upper end thereof to an elongated drive shaft coaxially positioned within the bore of an elongated hollow tubular housing which has at an upper end thereof a laterally outwardly angled vacuum inlet tube, the drive shaft protruding upwards through a rotatable vacuum-sealing type bearing located in an upper wall of the vacuum inlet tube to thus enable the shaft to be coupled to a rotary power tool such as an electric drill. 
     Another object of the invention is to provide a vacuum assisted post hole digger tool which includes an elongated zig-zag shaped mud and clay unclogger bar that is attached at an upper end thereof to an elongated drive shaft coaxially positioned within the bore of an elongated hollow tubular housing which has at an upper end thereof a laterally outwardly angled vacuum inlet tube, the drive shaft being coupled to an electric motor mounted on the vacuum inlet tube. 
     Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims. 
     It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, I do not intend that the scope of my exclusive rights and privileges in the invention be limited to details of the embodiments described. I do intend that equivalents, adaptations and modifications of the invention reasonably inferable from the description contained herein be included within the scope of the invention as defined by the appended claims. 
     SUMMARY OF THE INVENTION 
     Briefly stated the present invention comprehends a vacuum assisted post hole digger tool and apparatus for boring relatively deep, longitudinally elongated holes such as post holes into soil. 
     The vacuum assisted post hole digger apparatus according to the present invention utilizes a novel post hole digger tool which includes an elongated hollow tubular housing that has at the; upper end thereof a laterally outwardly curved vacuum inlet coupling tube. The apparatus includes a vacuum source such as a wet-or-dry shop vacuum powered by an electric motor which is connectable through a flexible vacuum hose to the vacuum inlet coupling tube of the tool. 
     The post hole digger tool according to the present invention includes a cylindrical ring-shaped bore head which is attached to the lower transverse end of the tubular housing. The bore head includes a cylindrical sleeve which is coaxially aligned within the tubular housing, and is of approximately the same diameter as the housing. The bore head has protruding downwards of the lower transverse annular edge wall thereof a plurality, typically four, of circumferentially spaced apart cutting blades or teeth. In a preferred embodiment, the teeth are attached to the outer circumferential surface of the cylindrically shaped sleeve which comprises the body of the bore head. 
     The vacuum assisted post hole digger tool according to the present invention includes a longitudinally elongated, zig-zag shaped mud and clay unclogger bar which is attached at an upper end thereof to an elongated drive shaft that extends upwardly through the center of the elongated bore through the tubular housing of the tool. The upper end of the drive shaft protrudes through the center of a vacuum-tight bearing fitted in an upper wall of the vacuum inlet tube, in coaxial alignment with the bore through the cylindrical housing. 
     The post hole digger tool according to the present invention includes a pair of transversely aligned cylindrically-shaped turnstile-type handles which protrude perpendicularly outwards form opposite sides of the tubular housing. The handles are located in a horizontal plane a short distance below the upper transverse end of the housing below the vacuum inlet coupler tube. 
     The vacuum assisted post hole digger tool according to the present invention is used by first connecting the outer, inlet end of the vacuum inlet coupler tube through a flexible hose to a vacuum source, such as an electrically powered wet-or-dry shop vacuum unit which includes a blower that has a vacuum inlet port and a cannister for collecting debris discharged from the output port of the blower. Next, the handles of the tool are grasped, and the tool lifted to position it vertically above a ground surface in which a hole is to be bored. The tool is then lowered to place the bore head teeth in contact with a ground surface. The tool handles are then toggled cyclically in clockwise and counterclockwise directions, e.g., plus and minus 90 degrees, to thus cause the bore head cutting teeth to penetrate the ground, assisted by downward force exerted by the weight of the housing. 
     The vacuum source is then turned on, and maintained on while the tool handles are rocked back and forth. Earth loosened by the cutting teeth is drawn up through the hollow bore of the tool housing by the vacuum source, facilitating boring action of the teeth. 
     When the vacuum assisted post hole digger tool is used in wet, muddy soil or in clay, the upper end of the drive shaft of the mud unclogger bar which protrudes upwards form the vacuum inlet tube is coupled to a rotary power source, such as by being clamped in the chuck of an electric drill. The rotary power source is then energized while the tool is in use, causing the mud unclogger bar to rotate, pulverize and break up mud or clay clogs which could otherwise form and prevent vacuum removal of severed soil material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a vacuum assisted post hole digger apparatus with a rotary clog breaker according to the present invention. 
         FIG. 2  is a perspective view of the vacuum assisted post hole digger tool part of the apparatus of  FIG. 1 . 
         FIG. 3  is a longitudinal medial sectional view of the tool of  FIG. 2 . 
         FIG. 4  is an upper plan view of the tool of  FIG. 3 . 
         FIG. 5  is a fragmentary side elevation view of the post hole digger of  FIG. 1  on an enlarged scale, showing a bore head component thereof. 
         FIG. 6  is a lower plan view of the bore head component of  FIG. 5 . 
         FIG. 7  is a partly exploded perspective view of an upper part of the post hole digger tool of  FIG. 1 , showing a mud and clay unclogger bar of the tool removed from the tool housing. 
         FIG. 7A  is a fragmentary perspective view of the post hole digger tool of  FIG. 7 , on an enlarged scale, and showing an upper end of the housing modified to include alternating grooves and flanges. 
         FIG. 8  is a fragmentary perspective view of a lower part of the tool of  FIG. 2 , showing the mud and clay unclogger bar thereof extended from the bore head thereof. 
         FIG. 9  is a perspective view of the post hole digger tool of  FIG. 1 , showing the tool connected to a vacuum source and positioned above a ground surface preparatory to using the tool to dig a hole in the ground. 
         FIG. 10  is a view similar to that of  FIG. 9 , showing the post hole digger tool of  FIG. 1  being readied to dig a hole in muddy soil. 
         FIG. 11  is a longitudinal sectional view of the arrangement of  FIG. 9 , showing how the tool of  FIG. 1  is used to severe soil. 
         FIG. 12  is a view similar to that of  FIG. 11 , showing severed soil being drawn up through the bore of the tool by vacuum. 
         FIG. 13  is a longitudinal sectional view of the tool of  FIG. 10 , showing a mud and clay unclogger bar of the tool being rotated to break up mud clogs. 
         FIG. 14  is an elevation view of a modification of the tool of  FIG. 2 , which has a larger diameter bore head. 
         FIG. 15  is a fragmentary view of the tool of  FIG. 14 , showing a bore head thereof. 
         FIG. 16  is a lower plan view of the bore head of  FIG. 15 . 
         FIG. 17  is a perspective view of another modification of the tool of  FIG. 2 , which has an integral drive motor for rotating the mud and clay unclogger bar of the tool. 
         FIG. 18  is an elevation view of a modified bore head for the tools of  FIGS. 1-14 . 
         FIG. 19  is a lower plan view of the bore head of  FIG. 18 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1-8  illustrate a basic embodiment of a vacuum assisted post hole digger tool and apparatus with rotary clog breaker according to the present invention.  FIGS. 9-13  illustrate operation of the post hole digger tool and apparatus according to the present invention.  FIGS. 14-16  illustrate a modification of the tool of  FIGS. 1-8 , which is useable for making larger diameter holes.  FIG. 17  illustrates a modification of the tool of  FIGS. 1-8  which includes an integral drive motor for rotating a mud and clay unclogger bar of the tool. 
       FIGS. 18 and 19  illustrate a modified bore head for use with tools shown in  FIGS. 1-17 , for use in making large holes. 
     Referring first to  FIG. 1 , a vacuum assisted post hole digger apparatus  20  may be seen to include a novel post hole digger tool  21  according to the invention, a vacuum source such as an electrically powered wet-or-dry shop vacuum unit  22 , and a flexible vacuum hose  23  which interconnects the tool  21  and the vacuum source  22 . 
     As shown in  FIGS. 1-3 , vacuum assisted post hole digger tool  21  includes a straight, longitudinally elongated, circular cross-section cylindrical housing  24 , which is made of heavy gauge steel or cast iron. Although the dimensions of housing  24  are not critical, example embodiments of the invention which were tested by the present inventor had outer diameters ranging between about 4 inches to 7 inches, and lengths of about six feet. 
     As shown in  FIG. 7 , housing  24  of tool  21  has located a short distance below upper transverse annular end wall  25  thereof a pair of straight, horizontally oriented left and right handle bars  26 L,  26 R, which are attached to and protrude perpendicularly outwards from diametrically opposed sides of the outer circumferential wall surface  27  of housing  24 . Preferably, as shown in the figures, handlebars  26 L,  26 R have fitted over them insulating tubular rubber handle grips  26 LG,  26 RG. 
     As shown in  FIGS. 3 ,  7  and  8 , housing  24  of tool  21  has disposed through its length a uniform diameter, circular cross-section bore  28  which has an upper opening  29  and a lower opening  30 . 
     Referring to  FIGS. 1 ,  3  and  7 , it may be seen that post hole digger tool  21  includes a vacuum inlet tube  31 , which preferably has the shape of a tubular right-angle elbow, that has a lower vertical section  32 , and an upper horizontal section  33  which protrudes laterally outwards from the upper end of the vertical section. 
     As shown in  FIGS. 3 and 7 , tool  21  includes a coupler  34  for coaxially coupling the inner, vertical section of vacuum inlet coupler elbow  31  in a vacuum-light connection to the upper open end of tubular housing  24 , thus forming a smooth, hermetically sealed passageway between the elongated straight bore  24  of the housing and the curved bore  35  of the vacuum inlet elbow. 
       FIGS. 3 ,  4  and  7  show a preferred construction of coupler  34  which includes a lower flange section  36  of vertical section  32  of vacuum inlet coupler  31  that has an enlarged diameter bore  37  that insertably receives the upper end of tubular housing  24 . In a most preferred embodiment, coupler  34  is a rotary union-type which enables the lateral arm  33  of vacuum inlet tube elbow  31  to be rotated in a horizontal plane relative to the longitudinal axis of tubular housing  24 . Preferably, as shown in  FIG. 7A , the upper end of tubular housing  24  has formed in outer cylindrical wall surface  27  thereof a series of alternating, longitudinally spaced apart circular grooves  27 G and flange barbs  27 F, for frictionally securing against relative longitudinal movement a vacuum hose or vacuum inlet tube  31  connected to tubular housing  24 . 
     Referring still to  FIGS. 3 and 7 , it may be seen that post hole digger tool  21  includes a bore head assembly  38  which is attached to a lower end  39  of tubular housing  24 . As may be seen best by referring to  FIGS. 6 and 7 , bore head assembly  38  includes a cylindrical isolation collar  40  which fits coaxially over the outer circumferential wall  27  of tubular housing  24 , and protrudes below the lower transverse end wall  41  of the housing. Isolation collar  40  is made of an electrically insulating material such as heavy rubber, and provides electrical isolation between housing  24  and a toothed bore head  42 . The function of isolation collar  40  is to prevent an operator of tool  21  from receiving an electrical shock should bore head  42  inadvertently contact a live buried electrical cable, as will be explained below. 
     As shown in  FIGS. 5 ,  6 ,  7  and  8 , bore head  42  of bore head assembly  38  includes a cylindrically-shaped base ring  43  that has attached to the outer cylindrical wall surface thereof a plurality of wedge-shaped cutting teeth  45 . As shown in  FIG. 5 , each cutting tooth  45  includes an upper rectangular bar-shaped upper root section  46 , a longer vertical edge  47  which protrudes downward below the lower transverse annular edge  48  of the base ring  43 , a shorter vertical edge  49 , and a lower straight edge  50  which angles obliquely downwards from the shorter vertical edge  49  to intersect at an acute angle the longer vertical edge  47  and form therewith a triangular vertex  51  which forms the cutting point of tooth  45 . 
     Although the number and spacing of cutting teeth  45  may be varied, in an example embodiment of tool  21  which was tested by the present inventor and depicted in  FIGS. 5-8 , bore head  42  had four cutting teeth  45 - 1 ,  45 - 2 ,  45 - 3  and  45 - 4 , spaced circumferentially apart at 90-degree intervals. 
     Referring to  FIG. 7 , it may be seen that tool  21  may optionally include an inner, connector sleeve  52  which is fastened coaxially within base ring  43 , as by circumferentially spaced apart bolts  53  disposed radially through aligned holes  54  and  55  through the cylindrical walls of  56 ,  57 , respectively of the base ring  43  and connector sleeve  52  with the lower transverse annular edge wall  59  of the connector sleeve aligned with lower transverse edge wall  59  of the bore head sleeve. Similarly, connector sleeve  52  is fastened at an upper end thereof within bore  40 A of isolation collar  40  by bolts  60  disposed radially through aligned holes  61 ,  62  through the cylindrical wall  40 B of isolation collar  40 , and aligned holes through connector sleeve  52 , located near the upper annular edge wall  63  of the connector sleeve. 
     As shown in  FIGS. 3 ,  7  and  8 , isolation collar  40  is attached to an inner connector sleeve  52  and the lower end of tubular housing  24  in a manner which creates an annular ring-shaped air gap  52 U between the upper transverse annular end wall of the sleeve  52  and the lower transverse annular end wall  41  of tubular housing  24 . Air gap  52 U electrically isolates bore head  42  from tubular housing  24 . 
     As may be understood by referring to FIGS.  3 , 6 , and  7 , bore head  42  has longitudinally through its length a central coaxial bore  42 B which preferably has a diameter at least as large as the diameter of bore  28  through housing  24 , bore  42 B communicating at an upper end with bore  28 , and having a lower entrance opening  42 D. 
       FIGS. 3 ,  7  and  8  illustrate the construction of a novel mud and clay unclogger component  64  of the tool  21 . 
     As shown in  FIGS. 3 ,  7  and  8 , mud and clay unclogger  64  includes an elongated longitudinally disposed rectangular cross-section, zig-zag shaped unclogger bar  65  which end is joined at upper end thereof by a coupler collar  66  to an elongated drive shaft  67 . Drive shaft  67 , which preferably has a round cross-section, is disposed longitudinally upwards through the center of bore  28  through housing  24 . As shown in  FIGS. 1-4 , the upper end of drive shaft  67  is rotatably mounted in the center of bearing  68  that is fitted into the upper wall  70  of vacuum inlet coupler elbow  31 . Bearing  68  is coaxially aligned with the longitudinal center line of housing  24  and forms a vacuum-tight seal with upper wall  69  of elbow  31 , so that air cannot leak from the exterior of elbow into the bore  35  through the elbow, when the air pressure in the bore is reduced below ambient atmospheric pressure by coupling the elbow to a vacuum source, such as a shop vacuum  22  shown in  FIG. 1 . 
     As may be seen best by referring to  FIGS. 7 and 8 , mud and clay unclogger bar  65  has a zig-zag shape formed by a series of flat sections which angle outwardly and inwardly with respect to the common longitudinal center lines of mud and clay unclogger bar coupler  66  and drive shaft  67 , to form a zig-zag shape. Thus, as shown in  FIG. 8 , mud and clay unclogger bar  65  has a first upper straight vertical segment  70  coaxially aligned with coupler  66  and drive shaft  67 , and a first, upper straight angled section  71  that angles radially outwardly and downwardly from the lower end of the upper straight section  70 . Mud and clay unclogger bar  65  also has a second straight vertical section  72  which extends downwardly from parallel to the longitudinal center line of housing  24  and drive shaft  67 , but is located on a first, e.g., right side of the common longitudinal center lines. 
     Referring still to  FIG. 8 , it may be seen that mud and clay unclogger bar  65  also has a second straight angled section  73  which extends radially inwardly and at a slight downward angle from the lower edge of second straight vertical section  72 , and extends radially beyond the longitudinal center line of stirrer collar  66  to the left side of the center line. A third, left straight vertical mud and clay unclogger bar segment  74  extends downwardly from the lower left end of second angled mud and clay unclogger bar segment  73 , and is joined at a lower end thereof by third right-wardly and downwardly angled straight section  75 . The lower end of section  75  is terminated by a terminal downwardly and radially inwardly angled, bottom angled straight segment  76 , which forms with segment  75  a V-shaped lower end section. As shown in  FIGS. 1 and 2 , the lower end  77  of lowest mud and clay unclogger bar segment  76  is approximately aligned with the lower transverse edges of cutting teeth  45 . 
       FIGS. 9-13  show how vacuum assisted post hole digger apparatus  20  according to the present invention is used. As shown in  FIG. 9 , left and right handles  26 L,  26 R of post hole digger tool  21  are grasped in the left and right hands, respectively, of an operator A. The tool  21  is then positioned vertically above a location in which a hole is to be dug, and the points of the cutting teeth  45  inserted into the soil, using a downward force exerted on the teeth by the weight of tool housing  24 , and, if necessary, additional downward force exerted on handles  26 L,  26 R by the operator. 
     Next, as shown in  FIGS. 1 and 9 , a vacuum hose  23  is connected at one end to elbow  31 , and at the other end to a vacuum source such as a wet-or-dry shop vacuum  22 . 
     Then, as shown in  FIGS. 9 and 11 , handles  26 L,  26 R are used to oscillate, toggle or rock housing  24  alternately in clockwise and counterclockwise directions relative to the longitudinal axis of the housing, in angular excursions of approximately 90-180 degrees clockwise and 90-180 degrees counterclockwise. This action causes cutting teeth  45  of severed soil, as shown in  FIG. 11 . Negative pressure within bore  28  of tubular housing  24  and bore  42 B of bore head  42  causes severed soil to be drawn up through the bore  28  of tool housing  24 , as shown in  FIGS. 12 , thus facilitating rapid downward vertical digging motion, as shown in  FIGS. 11 and 12 . 
     As shown in FIGS.  1 , 2 , 5  and  6 , the location of cutting teeth  45  on the outer cylindrical wall surface of base ring  43  forms a longitudinally disposed, annular arc-shaped gap between circumferentially spaced apart longitudinal edges of each pair of adjacent teeth. These gaps enable free flow of severed soil from the bore hole into the bore  28  of housing  24 , thus minimizing the possibility of forming a vacuum blockage of bore  28 , which would require withdrawing the housing vertically upwards in a bore hole being formed to clear the vacuum blockage. 
       FIGS. 10 and 13  illustrate how apparatus  20  is used to dig holes in wet or clay bearing soil. As shown in  FIG. 9 , the positioning of tool  21  relative to a ground surface of wet soil in which a hole is to be dug is similar to that shown in  FIG. 9 , in using the tool to dig a hole in dry soil. Moreover, the toggling or pivoting of the housing  24  of the tool  21 , and general procedure for using the tool, are similar for both dry and wet soil. However, as shown in  FIG. 10 , when the bore  28  of tool housing  24  tends to become clogged because of wet, muddy or clay soil lodging within the bore, the upper end of stirrer rod drive shaft  67  that protrudes upwardly from vacuum inlet coupler elbow  31  is connected to a rotary power source, such as by clamping the end of the drive shaft in the chuck C of an electric drill B. The rotary power source is then energized, causing the zig-zag shaped mud and clay unclogger bar  65  located at the bottom end of rotating drive shaft  67  to slice through and pulverize mud clogs and clay, thus restoring efficient vacuuming of dirt and mud or clay through the bore  28  of tool housing  24 . 
       FIGS. 14-16  illustrate a modification  81  of the vacuum post hole digger tool shown in  FIGS. 1-13  and described above. Modified post hole digger tool  81  has a bore head  102  of larger diameter than bore head  42  shown in  FIGS. 1-8 , and includes a frusto-conically shaped tubular transition section  140 . Transition section  140  has an upper diameter approximately equal to that of tubular housing  84  of tool  81 , and a larger lower diameter equal to that of larger diameter bore head  102 . 
       FIG. 17  illustrates another modification  20 A of tool  20  shown in  FIGS. 1-8  and described above. Modified tool  20 A has an integral drive motor  180  which replaces an external rotary power source such as the electric drill B shown in  FIG. 10 . As shown in  FIG. 17 , motor  180  is attached to a vacuum inlet tube elbow  31  by a bracket assembly  181 . Electrical power is supplied to drive motor  180  by a power cord  182 , which preferably is attached to the exterior of vacuum hose  23 . Preferably, power cord  182  includes a neutral conductor  183  which is connected directly to motor  180 , and a hot conductor  184  which is connected to the drive motor through an on/off switch  185  mounted on a handle bar grip  26 RG. 
       FIGS. 18-19  illustrate a modified bore head  242  for use with the vacuum assisted post hole digger tools  21 ,  81  and  211  described above. As shown in  FIGS. 18 and 19 , modified bore head  242  has a longitudinally elongated circular cross-section, hollow tubular teeth-anchor body  243 . Teeth anchor body  243  has an elongated upper elongated cylindrically-shaped connection tube section  230 , which at a lower transverse end thereof tapers radially inwardly to a smaller diameter, short neck section  231 . 
     The lower end of neck section  231  tapers radially outwardly to a longer teeth support section  232  of larger diameter than both upper connection tube section  230  and intermediate neck section  231 . As may, be seen best by referring to  FIG. 19 , teeth support section  232  has a generally uniform wall thickness. Thus, a lower generally cylindrically-shaped section  233  of teeth support section  232  has a generally cylindrically-shaped bore  234  which at the upper end thereof tapers radially inwardly via an angled annular transition section  235  to join a cylindrical inner bore  236  which is disposed longitudinally through neck section  231  and upper connection tube section  230 . 
     As shown in  FIGS. 18 and 19 , bore head  242  has attached to the outer cylindrical wall surface  244  of lower tooth support section  232  thereof a plurality of cutting teeth, including a first set of four axial cutting teeth  245 A,  245 B,  245 C,  245 D, which are spaced circumferentially apart at 90-degree intervals. As shown in  FIGS. 18 and 19 , axial cutting teeth  245  are approximately parallel to the longitudinal axis of cutting tooth anchor body  243 . Each axial cutting tooth  245  has a short, rectangular bar-shaped, upper root section  246 , which is fastened to a flat  296  to the outer cylindrical wall surface  244  of the lower tooth support section  232 . 
     Referring still to  FIGS. 18 and 19 , if may be seen that bore head  242  also has attached to outer cylindrical wall surface  244  of the bore head a second set of four angled cutting teeth  265 A,  265 B,  265 C,  265 D, which are located circumferentially midway between each pair of axial cutting teeth  245 , and hence are also spaced apart circumferentially at 90-degree intervals. As shown in  FIG. 19 , each angled cutting tooth  265  has a relatively long, radially inwardly bent upper root section  266 , which is fastened to both a flat  296  of the lower part of outer cylindrical wall surface  244  of lower tooth support section  232 , at an intermediate longitudinal location of each tooth, and to an upper arcuately inwardly curved wall surface  297  of outer wall surface  298  of tooth support section  222  at an upper location of each tooth, each tooth having at an outer lateral edge thereof an acutely angled, wedge-shaped cutting point. 
     Referring to  FIGS. 18 and 19 , it may be seen that each cutting tooth  245 ,  265  has a similar symmetrical shape. Thus, as shown in  FIG. 18 , each cutting tooth  245 ,  246  has circumferentially spaced apart, longitudinally disposed straight, parallel left and right sides  247 ,  249  which are coextensive with left and right sides of upper tooth section  246  of each tooth. As shown in  FIG. 18 , each tooth  245 ,  265  has a lower transverse edge  250  which is spaced longitudinally below the lower transverse annular end wall  248  of lower tooth support section  232  of bore head  242 . Lower transverse edge  250  has extending longitudinally upwards therein a symmetrically shaped notch  270  having the shape of an isosceles triangle, thus forming left  271  and right  272  cuspids of a bicuspid-shaped tooth, each having at an outer edge thereof an arcuately angled, wedge-shaped cutting point. 
     As may be seen best by referring to  FIG. 19 , each tooth  245 ,  265  has in transverse section the shape of regular prism; including a central section having flat and parallel inner and outer longitudinally disposed rectangular sides  272 ,  273 , and left and right triangular cross-section side section  274 ,  275 , the outer longitudinally vertices  276 ,  277  of which form longitudinally disposed, wedge-shaped knife edges.

Summary:
A tool for boring holes in soil includes an elongated tubular housing which has disposed through its length a bore having an upper opening coupleable to a vacuum source and a lower opening coupled to the bore of a ring-shaped bore head having circumferentially spaced apart cutting teeth protruding downwards from the bore head. A zig-zag shaped unclogger bar disposed coaxially through the bore head and rotated by a drive shaft disposed coaxially through the tubular and housing and protruding through a bearing in an upper end of the housing and driven by a rotary power source such as an electric motor fixed to the housing fragments lumps of clay or wet soil lodged in the bore of the housing, facilitating removal of soil and clay, which are severed by twisting the tool around its longitudinal axis by manipulating handle bars protruding from the upper end of the housing.