United States Patent 3667559

Earth auger pilot bit is an improvement upon U.S. Pat. No. 2,773,673. The body of the bit is cone-shaped with a "fish tail" lower extremity. The improvement consists of having two (or more) spiral cutting blades protruding from the cone-shaped body and extending into the fish-tail, the second blade on each side joining the leading blade of the other at the bottom of the bit to reinforce same. The plural blades resist fracture upon severe impact and divide the wear, thereby prolonging the life of the bit.

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International Classes:
E21B10/44; (IPC1-7): E21C13/04
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US Patent References:
2877987Conversion head1959-03-17Petersen
2870995Drive lug for pilot bit and earth boring augers1959-01-27Petersen
2773673Pilot bit1956-12-11Petersen
2639122Pilot bit for earth augers1953-05-19Petersen

Primary Examiner:
Champion, Marvin A.
Assistant Examiner:
Favreau, Richard E.
What is claimed is

1. A pilot bit for an earth auger comprising a body having a flat top of generally parallelogram shape formed with a recess to receive attachment means to attach said bit to an auger, said body having a substantially conical upper portion and having at angularly spaced positions first and second leading blades on the exterior of said body, each said leading blade originating at an acute angle of said top and extending in spiral shape of about 180° arcuate length downwardly of said body, the projection of said leading blade outward of said body gradually increasing as said blade extends downward, said leading blade extending below the apex of said body in a primary fishtail and formed in a cutting edge parallel to, but spaced outward of, a diameter of said body and having an outer corner and an inner corner, said body having first and second secondary blades on the exterior of said body, each said secondary blade originating on the outside edge of one of said leading blades partway down from said top, each said secondary blade of spiral shape and gradually diverging at an angle rearward of the principal blade to which it is connected and increasing in projection from said body as said secondary blade extends downward and also increasing in distance behind said principal blade as said blades extend downwardly, said secondary blade extending below the apex of said body in a secondary fishtail which joins at its bottom end with the outer corner of the cutting edge of the primary fishtail of the leading blade opposite that to which said secondary blade is connected.

2. A bit according to claim 1 in which each said primary fishtail has an inner edge which slants downwardly-inwardly to the central axis of said bit at an angle of about 45°.

3. A bit according to claim 1 in which each secondary blade diverges from the leading blade with which it is connected at an angle which gradually increases to about 15° at the bottom of said bit.

4. A bit according to claim 1 in which each said blade is formed with front and back flanks which are disposed at an angle to each other of about 30°.

5. A bit according to claim 4 in which the outer edge of the secondary blade is slightly closer to the central axis of said bit than the corresponding outer edge of said leading blade measured in a plane perpendicular to said axis to provide rake.

This invention relates to a new and improved pilot bit having two or more cutting blades on each of the blades which protrude from the body of the bit. The pilot bit for earth augers shown in U.S. Pat. No. 2,773,673 has enjoyed wide-spread commercial success. One of the problems encountered in use of such bit has been that when the bit is subjected to the impact of contact with hard rock the points of the "fish-tail" extremities tend to break. Another problem encountered in use of the bit in extremely abrasive soil is the fact that the blade which projects from a generally conical body wears excessively with the passage of time.

The principal purpose of the present invention is to avoid these problems which have heretofore been encountered. Accordingly, the principal purpose of the present invention is to provide for each primary or leading blade of the bit a following blade positioned slightly rearwardly and which extends from about the midpoint of the body downwardly and into the fish-tail and connects with the opposite blade of the bit. The secondary, or following blade, thus reinforces the tip of the fish-tail extremity portion of the opposite blade and also provides a cutting edge which supplements the leading blade and thus divides the wear of the cutting edge.

Accordingly, a principal feature of the present invention is to resist more effectively the impact which tends to break off the points of the fish-tail extremities of the pilot bit; and further, to prolong the life of the bit by dividing the wear on each side of the bit by providing a plurality of cutting edges.

In addition, the present bit has the advantages of U.S. Pat. No. 2,773,673. More specifically, one of the features of the invention is that the bit breaks the earth effectively and also diverts the spoil broken by the bit laterally and upwardly away from the center of the hole being bored so that the auger to which the pilot bit is attached may effectively convey the spoil.

Another feature of this invention, as in the previous patent, is the self-sharpening features of the cutting extremity or fish-tail of the bit.

Still another feature of the invention is that the principal component of the stress imposed upon the blades of the bit are in compression rather than shear and hence the likelihood of fracture of the blades is diminished.

Other objects of the present invention will become apparent upon reading the following specification and referring to the accompanying drawings in which similar characters of reference represent corresponding parts in each of the several views.

In the drawings:

FIG. 1 is a bottom plan view of the pilot bit in accordance with the present invention.

FIG. 2 is a side elevational view thereof.

FIG. 3 is a side elevation taken with the bit rotated 90° relative to FIG. 2.

FIG. 4 is a vertical sectional view taken substantially along the line 4--4 of FIG. 1.

The pilot bit of the present invention is a unitary steel casting having an upper portion body 11, which merges into a lower "fish-tail" extremity 12. The upper body is an inverted cone having about a 90° angle.

The upper end 13 of the cone is flat and its plane is perpendicular to the axis 14 of the cone, which is also the axis of rotation of the bit and its axis of symmetry. End 13 resembles a parallelogram. Extending into upper end 13 is a socket 16 which receives a drive lug connected to an auger shaft (not shown). The construction of socket 16 is shown in detail in U.S. Pat. No. 2,870,995 and is not here detailed. In order to provide room for the socket, bosses 17 are formed on opposite sides of upper body 11 extending down from upper end 13 and terminating in diametrically opposed, approximately horizontal shoulders 18. Immediately below shoulders 18, flats 19 are formed on the body and extending diametrically through the body between flats 19 and into the lower portion of the recess 16 are holes 21. A bolt passes through holes and also through an apertured extension (not shown) of the drive lug to secure the pilot bit to said lug.

Only one side of the bit will be described since the opposite side is identical.

A leading or primary blade 26 is formed protruding from the body originates at the acute outside corner 27 of the parrallelogram upper end 13. The outer edge 28 of blade 26 curves downwardly-forwardly in the direction of rotation of the bit (counter-clockwise as viewed in FIG. 1). The length of the leading blade, as viewed in plan, is approximately 180° of arc. In elevation, the blade extends down below the theoretical apex of the conical body to provide the "fish-tail" 29 which is characteristic of U.S. Pat. No. 2,773,673. The fish-tail 29 is approximately 40 percent of the total vertical height of the bit. The extent to which the leading blade extends beyond the outline of the conical body increases as the blade proceeds downward. That is, at the upper corner 27 the blade outer edge and the body are co-extensive, but as the blade proceeds downwardly the dimension by which the outside edge 28 thereof protrudes beyond the theoretical conical shape of the body increases arithmetically.

In cross-section, blade 26 comes to a rather blunt point at its outside edge 28 and the front and back flanks 31, 32 slant toward the body at an angle of about 30° and merge with the body on front and back flanks in a radius 33. This form of cross-section of the blade gives strength to the blade and also directs the spoil cut by the bit upwardly and outwardly away from axis so that the auger above the pilot bit can handle the spoil.

At the lower end of the leading edge of blade 26, the latter is truncated in an approximately horizontal cutting edge 34 which is displaced forwardly of a radius from axis 14 in the direction of the turning of the bit. The outer corner 36 of the cutting edge is positioned on a diameter. The inner edge 37 of the fish-tail inward of cutting edge slants downwardly-inwardly at an angle of about 45° with respect to axis 14.

The foregoing description of the leading edge of the blade is substantially the same as the blade of U.S. Pat. No. 2,773,673.

A feature of the present invention is the provision of a trailing blade 41 which is behind leading blade 26 in the direction of rotation of the bit. Trailing blade 41 originates at a point 42 on the outer edge 28 of the leading blade which is approximately 1/2 the distance down from upper end 13. The outer edge 28a of trailing blade 41 diverges from the outer edge 28 of leading blade 26 and the angle of divergence increases proceeding downwardly to a maximum of about 15°. When the bit is new, the outer edge 28a of the trailing blade 41 is slightly closer to axis 14 than the corresponding edge 28 on the leading blade measured in a plane perpendicular to axis 14 to provide "rake." The outside edge 28a of the trailing blade connects with and terminates at the outer corner 43 of the cutting edge 28 of the opposite primary blade 26, and thus reinforces said corner 43. The groove 46 between leading blade 26 and trailing blade 41 is approximately V-shaped and with a radius at the bottom of the V, and the depth of groove 46 increases proceeding downward. The cross-section of secondary blade 41 is similar to that of the primary blade 26, and the same reference numerals, followed by Subscript a, are used to designate corresponding elements.

Thus, each side of the bit consists of two blades 26 and 41 which, proceeding toward bottom of the bit, are oppositely divergent, the trailing blade 41 veering off toward the opposite leading blade 26.

The horizontal cutting edge 34 of each leading blade, which takes the shock of impact in hard ground, is reinforced by reason of the fact that the outer corner 43 of the leading blade 26, is connected to the outer corner of the trailing blade 41 of the opposite side of the bit. On the other hand, the leading blade side edge 28 is followed in the direction of the rotation of the bit by the outer edge 28a of the trailing blade which is, when the bit is newly manufactured, only a slight distance less from the axis than that of the leading blade. As the bit wears, the outer edge 28 of the leading blade wears away and part of the cutting action is assumed by the outer edge 28a of the trailing blade. Hence, the life of the blades 26 and 41 and the fish-tail ends 12 of the bit are prolonged.