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BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention is in the area of equipment and methods for creating post holes, and pertains more particularly to making square holes of a size for square fence posts.  
         [0003]     2. Discussion of the State of the Art  
         [0004]     It is well known that there exist at the time of this application a number of alternative tools and methods for digging post holes. A well known tool is the two-handed post-hole spade that has long handles and opposed spades connected at a pivot, such that the spades may be opened by pulling the handle apart and closed by closing the handles. A worker uses both hands to drive the opposed spades into the earth, closes the spades to collect loose earth, and raises the tool out of the developing hole to set the loose earth aside; then repeats the process until the desired depth is attained. It is also well-known that this tool and method is clumsy, tiring, and generally results in a rather large round hole.  
         [0005]     Other than hand tools there exists a number of power tools, such as drills and augers of various sorts for making post holes. These are invariably rotary devices that produce round holes, but typically the holes produced by these power tools are more uniform and close to desired size than those produced by hand tools.  
         [0006]     Although there are round posts that certainly may be used in round post holes, many people prefer square posts, and for the purpose of this specification four-inch square posts will be considered.  
         [0007]     To set a four-by-four post in a post hole, one must produce a round post hole of a diameter great enough to insert the post. For a four-by-four post the diameter needed is the length of the corner-to-corner diagonal of the post, which is 5.67 inches to the nearest one-hundredth of a inch. There needs to be some clearance, so the smallest workable hole diameter is about six inches.  
         [0008]     Once one has made a six-inch diameter hole to a desired depth, the post is placed in the hole to the bottom of the hole, leaving relatively large spaces all around the post. Now it is necessary to add loose earth back into the spaces, which are typically rodded to compact the loose soil to better hold the post. This is a difficult process.  
         [0009]     What is clearly needed is an apparatus and method for forming a square post hole of very close to the size of the post, with sides that are formed closely compacted in the process, so the post can be driven into the square hole completing the process.  
       SUMMARY OF THE INVENTION  
       [0010]     In one embodiment of the invention a tool for expanding a hole having a vertical axis in the earth is provided, comprising at least one set of two opposed compactor units constrained to separate and retract in a direction at a right angle to the axis of the hole, and a drive mechanism coupled to the set of compactor units providing force to separate the compactor units, urging the units against a wall or walls of the hole, compacting the earth and enlarging the hole.  
         [0011]     Also in an embodiment of the invention the compactor units comprise lengths of angle iron that when fully retracted form together a substantially square shape, and the direction of separation and retraction is along the diagonal through the apex corners of the two angle irons. Also in an embodiment the drive mechanism comprises a linear actuator constrained to travel vertically, the actuator and individual compactor units joined by links pivoted both at the actuator and the individual compactor units. The drive mechanism may also have a fluid cylinder coupled to the linear actuator, the fluid cylinder driving the linear actuator vertically to the limits of the cylinder action. In still other embodiments there may be two or more sets of opposed compactor units.  
         [0012]     In another aspect of the invention a method for producing a hole in the earth for setting a post having a cross section of a particular shape and area is provided, comprising the steps of (a) making a hole of a cross section less in area than the area of the cross section of the post to be set; (b) placing in the hole an expansion tool; and (c) activating the expansion tool to expand and shape the cross section of the hole.  
         [0013]     In one embodiment of the method the expansion tool comprises at least one set of two opposed compactor units constrained to separate and retract in a direction at a right angle to the axis of the hole, and a drive mechanism coupled to the set of compactor units providing force to separate the compactor units, urging the units against a wall or walls of the hole, compacting the earth and enlarging the hole.  
         [0014]     Also in one embodiment of the method in step (a) the original cross section of the hole is round, and in step (c) the hole is expanded to a square cross section shape of an area greater than the original cross section area. In some cases in step (c) two or more operations are employed with the expansion tool rotated on the axis of the hole between operations, and in some of these embodiments the final shape of the hole is substantially square. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES  
       [0015]      FIG. 1  is a perspective view of an expander tool according to an embodiment of the present invention for making a round hole into a larger square hole.  
         [0016]      FIG. 2  is a vertical elevation section view of a portion of the height from the bottom of the expander tool of  FIG. 1 .  
         [0017]      FIG. 3  is a partial section taken along section line  3 - 3  of  FIG. 1  showing attachment of a drive cylinder to the tubing assembly.  
         [0018]      FIG. 4   a  is a cross-section view taken along line  4   a - 4   a  of  FIGS. 1 and 2 .  
         [0019]      FIG. 5   a  indicates relocation of the expander for a second operation according to an embodiment of the present invention.  
         [0020]      FIG. 5   b  shows the result after a second extension of the expander from the position shown in  FIG. 4   a.    
         [0021]      FIG. 6  is an elevation view of a manual tool  120  for creating an undercut at the bottom of the square hole developed using the expander described above.  
         [0022]      FIG. 7   a  is a section taken along line  7   a - 7   a  of  FIG. 6  showing a plan view of an adjustable cutting head for the tool of  FIG. 6 .  
         [0023]      FIG. 7   b  is a view of one end of the cutting head of  FIG. 7   a.    
         [0024]      FIG. 8  illustrates a square hole formed by an expander according to an embodiment of the present invention, with a manual undercut tool according to an embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]      FIG. 1  is a perspective view of an expander tool  101  according to an embodiment of the present invention for expanding a round hole into a larger square hole. Expander tool  101  comprises in this embodiment two angle iron assemblies  102  having two-inch legs engaged in a mechanism described in detail below. The mechanism, driven in this example by a pneumatic cylinder  105  through a tubing assembly  104  mounted to a round base plate  103 , causes angle irons  102  to separate when the cylinder is activated with sufficient force to push a small diameter hole into a larger square hole while also compacting the soil around the resulting square post hole.  
         [0026]      FIG. 2  is a vertical elevation section view of a portion of the height from the bottom of expander tool  101  of  FIG. 1  taken along the section line  2 - 2 . An activator rod  106  engaged to and driven vertically by cylinder  105  operates within tubing assembly  104 , which is welded into base plate  103  along region  107  in this embodiment. Pusher blocks  108  are affixed to rod  106  through slots in tubing assembly  104 , the slots being of sufficient length to accommodate the full necessary stroke of rod  106  to fully open and close the two angle iron assemblies  102 . Two sets of slots and pusher blocks are shown, but there may be several more, depending on the overall height of the expander tool, which determines the depth of a hole that may be expanded.  
         [0027]     Pusher blocks  108  are pivotally connected to pusher links  109  with pivot pins  110 , and at the opposite ends the pusher links are pivotally connected by pivot pins  111  to brackets  112  which are welded in this embodiment at strategic locations along each angle iron assembly  102 . The angle iron assemblies are closed at the lower end by welded plates  113 , such that when cylinder  105  is activated and drives rod  106  downward, the angle iron assemblies are constrained by these plates against base plate  103  to travel outward horizontally. A spring mechanism (not shown) retracts the angle iron assemblies horizontally when the cylinder is retracted.  
         [0028]      FIG. 3  is a partial section taken along section line  3 - 3  of  FIG. 1  showing attachment of cylinder  105  to tubing assembly  104 . In the tubing assembly, the main vertical tube is welded in this embodiment to base pate  103 , as described above, and as shown in  FIG. 3  is welded to an upper plate  119 , which is machined to match the mounting interface for the cylinder. The cylinder is mounted to plate  119  with conventional fasteners (not shown). The active shaft of the cylinder in this embodiment has a male thread, is threaded into a female thread in rod  106 , and is secured with a standard locking nut.  
         [0029]      FIG. 4   a  is a cross-section view taken along line  4   a - 4   a  of  FIGS. 1 and 2 , and shows the mechanism of the expander in closed position with rod  106  retracted and the angle iron assemblies drawn together presenting the smallest cross-sectional area. Dotted circle  115  indicates diameter of a hole that has to be produced to insert the expander mechanism of the invention. The diameter of this hole is about 3.25 inches, as opposed to a hole of nearly six inches diameter required for setting a 4×4 fence post in the conventional way. Since the volume of earth to be removed to make a hole in the ground is directly related to the area of the hole, for the conventional method more than three times the volume of earth has to be removed.  
         [0030]      FIG. 4   b  is along the same section line as  FIG. 4   a,  but shows the expander expanded to full range by driving rod  106  downward with cylinder  105 . The length of pusher links  109  is made to cause the diagonal distance from corner-to-corner in this position to be just a bit greater than the diagonal measurement of a 4×4 post section. Dotted boundary  116  illustrates the extent of the expanded hole in the earth at this point. It is to be noted (see also  FIG. 2 ) that in the first portion of a downstroke the mechanism produces the least thrust in the direction of the movement of the angle iron assemblies that move and compact the earth, but in this portion the resistance of the earth is also least. In the last portion of the downstroke, when more thrust will be needed, the mechanism produces a great mechanical advantage, and the thrust is maximized.  
         [0031]     After the action shown in  FIG. 4   b,  producing the shape for the developing hole shown by dotted line  116 , the expander is retracted and rotated ninety degrees as shown in  FIG. 5   a.  Now activating the expander again will cause the angle iron assemblies to travel in the direction of arrows  117 .  
         [0032]      FIG. 5   b  shows the result after the second extension of the expander from the position of  FIG. 4   a.  Now the developed hole is as shown by dotted line  118 , which is square, of a size to accommodate a 4×4 post, and the sides of the hole are very solidly compacted. No fill or rodding is necessary.  
         [0033]     A method then, using the apparatus in the embodiment of the invention shown, is to create a hole in the earth of diameter about 3.25 inches, insert the expander, extend and retract the expander, rotate the expander ninety degrees, and then extend and retract the expander again, creating a compacted square hole in the earth of a size to accommodate a 4×4 fence post.  
         [0034]      FIG. 6  is an elevation view of a manual tool  120  for creating an undercut at the bottom of the square hole developed using the expander described above. Tool  120  has a vertical hollow tubing  121  that can be rotated by a t-bar  122  mounted at the upper end. The tubing is shown in broken view because the height may be much greater than shown in the view. The t-bar in this example has added hand grips. An adjustable cutter head  123  is mounted at the bottom end, and is adjustable by rotation of a gear  126  by a shaft  124  passing within tubing  121 . Shaft  124  has a handle  125  at the upper end for easy adjustment.  
         [0035]      FIG. 7   a  is a section view taken along line  7   a - 7   a  of  FIG. 6 , providing a plan view of cutting head  123 . Head  123  comprises main body portion  127  and two adjustable cutting units  129 , one on each side of the body. The extended portion of each adjustable cutting unit has a curved scraping edge directed for clockwise rotation. Further each cutting unit has a linear gear face  130  that engages a gear  126  driven by shaft  124 . By rotating shaft  124  clockwise (in this view) the cutting units may be extended equally.  
         [0036]      FIG. 7   b  is a view of one end of the cutting head in the direction of arrow  7   b  of  FIG. 7   a,  which indicates how each cutting unit is restrained and guided. A portion of body  127  is machined to provide channels for panels  131  and  132  which are fastened together and to cutting unit  129  to guide the cutting unit relative to the body. In this view the curved end of the cutting unit has been cut off to be able to see the guide arrangement in full view.  
         [0037]      FIG. 8  illustrates a square hole  134  that has been formed by an expander according to an embodiment of the present invention. Manual tool  120  is shown extended to the bottom of hole  134  with the cutting units fully retracted, so the overall width of the cutting head is a bit less than four inches, so it may be introduced into hole  134  without interference. Once in position the operator turns handle  125  (which could also be a knob) clockwise to extend the cutting heads, and also turns the manual tool clockwise using handle  122 . The cutting heads scrape earth at the bottom of the hole providing an undercut, the diameter of which is made greater by further turning handle  125 , and turning the tool with handle  122 .  
         [0038]     When the cutting units are fully extended a significant undercut is accomplished, and a quantity of loose earth is left in the bottom of the hole. The cutting units are then retracted and the tool removed. The loose earth may be easily removed by a vacuum hose extended into the bottom of the hole from a shop vacuum apparatus.  
         [0039]     Now the user may add concrete or other material into the hole which will flow into the undercut. The material may be, for example, an epoxy thermosetting material. After adding the concrete or plastic the post needs to be set before the added material hardens.  
         [0040]     A post set without the undercut will be very secure, because the sides of the square hole are compacted very efficiently in the process of forming the hole. A post set with the undercut and a setting material will be even more secure, and very difficult to remove.  
         [0041]     It will be apparent to the skilled artisan that many alterations might be made in the embodiments of the invention described above without departing from the spirit and scope of the invention. For example, the devices described might be sized to produce square holes of much different dimension than 4×4 inches. The devices described in embodiments of the invention might also be used to produce holes in the earth with much different cross-sections than square, including rectangular, polygonal, and even round. To produce a hole for a round post one might drill or auger a hole of considerably smaller diameter than the round post, and use an expander according to an embodiment of this invention, but with “pushers” with the form of circular arcs instead of the angle irons described to urge the earth in the walls of the smaller holes into a larger round hole with the walls greatly compacted. The method of undercutting and filling may be used with a hole of any shape as well.  
         [0042]     Further to the above there may be many alterations in the materials used, and in the design to produce the desired effects. There are similarly many other alterations within the spirit and scope of the invention, so the invention is entitled to the scope of the claims that follow:

Summary:
A tool for expanding a hole having a vertical axis in the earth has at least one set of two opposed compactor units constrained to separate and retract in a direction at a right angle to the axis of the hole, and a drive mechanism coupled to the set of compactor units providing force to separate the compactor units, urging the units against a wall or walls of the hole, compacting the earth and enlarging the hole.