Title:
Auger with Butterfly Flighting
Kind Code:
A1


Abstract:
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.



Inventors:
Fraley, Phillip J. (Winfield, AL, US)
Davis III, John W. (Winfield, AL, US)
Application Number:
13/223407
Publication Date:
03/01/2012
Filing Date:
09/01/2011
Assignee:
FRALEY J. PHILLIP
DAVIS, III JOHN W.
Primary Class:
International Classes:
E21B10/44
View Patent Images:
Related US Applications:



Primary Examiner:
HALL, KRISTYN A
Attorney, Agent or Firm:
BRADLEY ARANT BOULT CUMMINGS LLP (200 CLINTON AVE. WEST SUITE 900, HUNTSVILLE, AL, 35801, US)
Claims:
What is claimed is:

1. An auger comprising: a cylindrical shaft; an upper end coupled to a gearbox and rotatable by a power take-off of a tractor; a cutting head disposed near a lower end of the shaft, the cutting head comprising a plurality of blades, the blades extending downwardly and angularly from a blade disc, the blade disc comprising an opening associated with each blade, the blade angled downwardly into the opening, the cutting head comprising a substantially circular outer edge; an auger tip releasably affixed to and extending beneath the lower end of the shaft, the auger tip extending substantially parallel to the shaft and comprising at least one boring blade; a plurality of flights rigidly affixed to the shaft and extending helically around the shaft, the flights disposed above the cutting head and below the upper end, the flights comprising substantially flat plates rigidly affixed to the shaft at an angle to the shaft, the flights comprising curved outer edges substantially aligned with the outer edge of the cutting head, upper ends of the flights aligned in substantially a same horizontal plane, lower ends of the flights aligned in substantially a same horizontal plane, each flight extending more than 180 degrees and less than 270 degrees around the shaft.

2. The auger of claim 1, wherein the shaft comprises a smooth portion above the upper ends of the flights, the smooth portion being substantially free of protrusions.

3. The auger of claim 2, wherein the ratio of the smooth portion to a length of the shaft from its upper end to its lower end is greater than 66%.

4. The auger of claim 1, wherein the upper end of the shaft comprises a coupler, the coupler comprising internal threads mateable to the gearbox.

5. The auger of claim 1, wherein the upper end of each flight comprises a substantially straight trailing edge extending radially from the shaft and then curving towards the curved outer edge.

6. The auger of claim 5, wherein the plurality of flights comprises a first flight and a second flight, wherein the first flight is clocked 180 degrees from the second flight with respect to the shaft.

7. The auger of claim 6, wherein the trailing edge of the first flight and the trailing edge of the second flight are aligned with each other and with the center of the shaft.

8. The auger of claim 7, wherein the first flight is angled with respect to the second flight at an angle of substantially 40 degrees.

9. The auger of claim 1, wherein the plurality of blades in the cutting head are oriented such that they face in the same direction when the shaft rotates.

10. An auger comprising: a cylindrical shaft; an upper end coupled to a gearbox and rotatable by a power take-off of a tractor; a cutting head disposed near a lower end of the shaft, the cutting head comprising a plurality of blades, the blades extending downwardly from a blade disc, the blade disc comprising an opening associated with each blade, the blade angled downwardly into the opening, the cutting head comprising a substantially circular outer edge; an auger tip releasably affixed to and extending beneath the lower end of the shaft, the auger tip extending substantially parallel to the shaft and comprising at least one boring blade; a first flight and a second flight rigidly affixed to the shaft and extending helically around the shaft, the flights disposed above the cutting head and below the upper end, the flights comprising substantially flat plates rigidly affixed to the shaft at an angle to the shaft, the flights comprising curved outer edges substantially aligned with the outer edge of the cutting head, upper ends of the flights aligned in substantially a same horizontal plane, lower ends of the flights aligned in substantially a same horizontal plane, each flight extending less than 360 degrees around the shaft, the first flight clocked with respect to the second flight at substantially 180 degrees.

11. The auger of claim 10, wherein the shaft comprises a smooth portion above the upper ends of the flights, the smooth portion being substantially free of protrusions.

12. The auger of claim 11, wherein the ratio of the smooth portion to a length of the shaft from its upper end to its lower end is greater than 66%.

13. The auger of claim 10, wherein the upper end of the shaft comprises a coupler, the coupler comprising internal threads mateable to the gearbox.

14. The auger of claim 10, wherein the upper end of each flight comprises a substantially straight trailing edge extending radially from the shaft and then curving towards the curved outer edge.

15. The auger of claim 14, wherein the trailing edge of the first flight and the trailing edge of the second flight are aligned with each other and with the center of the shaft.

16. The auger of claim 10, wherein the first flight is angled with respect to the second flight at an angle of substantially 40 degrees.

17. The auger of claim 10, wherein the plurality of blades in the cutting head are oriented such that they face in the same direction when the shaft rotates.

Description:

CROSS-REFERENCE TO RELATED APPLICATIONS

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

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

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.

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.

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.

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 exemplary embodiment of the present disclosure.

FIG. 2 is a bottom perspective view of an auger according to an exemplary embodiment of the present disclosure.

FIG. 3 is a top perspective view of the auger of FIG. 2.

FIG. 4 is an enlarged partial side view of the auger of FIG. 2.

FIG. 5 is a top plan view of the auger of FIG. 2.

FIG. 6a is a front plan view of the blade mount angle of FIG. 4.

FIG. 6b is a side plan view of the blade mount angle of FIG. 4.

FIG. 7a is a front plan view of the blade mount bar of FIG. 4.

FIG. 7b is a side plan view of the blade mount bar of FIG. 4.

FIG. 8a is a front plan view of the blade of FIG. 4.

FIG. 8b is a side plan view of the blade of FIG. 4.

FIG. 8c is front plan view of an alternative embodiment of the blade of FIG. 4.

FIG. 9 is bottom plan view of a blade disc according to an exemplary embodiment of the present disclosure.

FIG. 10 is a bottom plan view of the auger of FIG. 2.

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.

FIG. 12 is a cross sectional view of the auger of FIG. 12, taken along section lines A-A of FIG. 11.

FIG. 13 is a cross sectional view of the auger of FIG. 11, taken along section lines B-B of FIG. 11.

FIG. 14 is a cross-sectional view of the auger of FIG. 5, taken along section lines C-C of FIG. 5

FIG. 15 is a side plan view of a coupling for the auger according to an embodiment of the present disclosure.

FIG. 16 is a detail drawing of a flight according to an embodiment of the present disclosure.

FIG. 17 is a side plan view of a post hole digger showing an auger according to an embodiment of the present disclosure.

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

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).

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.

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'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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 75a and 75b, respectively and an upper end 76a and 76b, respectively. The soil moves from the lower ends 75a and 75b upwardly to upper ends 76a and 76b and continues to accumulate in a column as described herein until the auger 10 is removed from the hole.

In the illustrated embodiment, the upper ends 76a and 76b are disposed at substantially the same level as one another, i.e., are disposed in a generally horizontal plane. Similarly, the lower ends 75a and 75b are disposed in the same generally horizontal plane.

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.

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.

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.

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 76a, 76b of the flights 71 and 72 are substantially 180 degrees apart, and the lower ends 75a, 75b of the flights 71 and 72 are substantially 180 degrees apart.

Further, each of the flights extends generally 180 degrees+“α” around the shaft 11, where α is the angle that the lower end 75a of the flight 71 overlaps the upper end 76a of the flight 72. (Note that α is measured from a reference line 69 tangential to the lower end 75a and passing through the center of the shaft 11.) Similarly, α is also the angle that the lower end 75b of the flight 72 overlaps the upper end 76b 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.

FIG. 6a 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.

FIG. 6b 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.

FIG. 7a 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.

FIG. 7b 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.

FIG. 8a 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 V2 inch thick steel.

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.

FIG. 8b 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.

FIG. 8c 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. 8a), 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.

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 21a and 21b 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 21a and 21b.) In one embodiment, the blade disc 13 is formed from a 12 inch diameter circular steel plate that is ⅜″ thick.

The two openings 21a and 21b 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 21a and 21b, and the openings 21a and 21b may be differently spaced.

The opening 21b 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. 5b) of the blade mount angle 27 is welded to the wall 32.

The opening 21b 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.

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.

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.

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 21b. Further, the straight portion 58 of the left side 51 (FIG. 8a) 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.

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.

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.

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 14a and 14b are substantially similar and face in opposite directions as shown. The blades 14a and 14b are disposed within the openings 21a and 21b of the blade disc 13. A plurality of fasteners 20 releasably attaches the blades 14a and 14b to the mounting brackets 19a and 19b.

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 75a and 75b of the flights 71 and 72, respectively, are clocked generally 180 degrees from one another with respect to the shaft 11.

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.

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.

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 76a to a lower end 75a. The upper end 76a 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 75a before terminating at a corner 86.

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.

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.

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.

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.

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.