Excavating tooth and shank plate assembly

An excavating tooth includes an aperture for bolting the tooth to a shank plate and a lug configured to provide a friction fit in a recess formed in the shank plate. The bolt and lug combination prevent relative movement between the tooth and shank plate. In addition, tooth load is absorbed in the shank plate through the connection between the lug and shank plate, thereby reducing the stress transferred through the bolt.

CROSS-REFERENCE TO RELATED APPLICATION 
This patent application is related to U.S. patent application Ser. No. 
08/229,262, filed Apr. 18, 1994, titled Reversible Tooth with Adjustable 
Attack Angle. 
BACKGROUND OF THE INVENTION 
The present invention relates to an excavating tooth for earth-digging 
equipment such as earth augers and the like, and a mounting arrangement 
therefor. 
Typically, earth-digging machines employ boring heads having a plurality of 
teeth which dig into the earth being excavated. These teeth absorb most of 
the load encountered by the machine and are the portion of the machine 
most likely to be worn or broken. Accordingly, tooth configurations and 
mounting arrangements therefor have been developed to facilitate 
replacement of broken teeth. Reversible tooth arrangements also have been 
developed that permit a tooth worn on one side to be turned over and used 
on the other side. 
Generally, such teeth include a distal cutting portion and a proximal 
portion that is configured for bolting the tooth to a holder such as a 
shank plate as disclosed in U.S. Pat. Nos. 2,952,085 and 3,063,175 to 
Petersen, for example. Typically, the proximal portion includes a pair of 
laterally spaced prongs that form a slot therebetween through which a bolt 
extends to connect the tooth to the tooth holder. A back wall is provided 
on the tooth holder behind the prong ends of the tooth as disclosed in 
U.S. Pat. No. 3,063,175 to Petersen, for example. This wall is intended to 
prevent tooth rotation about the rotational axis of the bolt. The tooth 
holder can be cast steel in which the back wall typically is formed in the 
holder during casting. Alternatively, the tooth holder can comprise a 
stamped steel plate, in which case a tab is generally welded to the plate 
to form the back wall of the tooth holder. However, due to manufacturing 
tolerances of the teeth as well as the tooth holder, both tooth prong ends 
generally do not seat against the back wall when the tooth is bolted to 
the holder. As a result, a substantial amount of the load on the tooth can 
be transferred to the holder through the bolt, thereby causing bolt 
failure and machine down time. Such spacing between the prong ends and the 
back wall also can result in tooth oscillation as contact is alternately 
made between each tooth prong and the back wall. The resultant cyclic 
impact between the prongs and the back wall can significantly reduce the 
life of the tooth. In addition, where the welded tab configuration is used 
to form the back wall, the load transferred from the tooth to the tab, can 
break the tab from the tooth holder. It is also noted that on the tooth 
holders that have back wall tabs welded to the plate, the bolt generally 
acts as a clamp and prevents the tooth from moving forward and away from 
the tab. However, if the bolt is loosened the slightest amount, as a 
result of vibration for example, the tooth can move forward such that the 
prongs are no longer in contact with the back wall. The tooth will then 
oscillate about the bolt and loosen the bolt even further. As a result, 
the tooth can fall off of the auger or simply loosen to the point where it 
becomes ineffective. 
SUMMARY OF THE INVENTION 
The present invention is directed to an excavating tooth and mounting 
arrangement that avoids the problems and disadvantages of prior art. The 
invention accomplishes this goal by providing a tooth configured for 
forming a positive interlock with a tooth holder, such as a shank plate, 
at all times. More specifically, the tooth includes a distal portion and a 
proximal portion having a mounting surface and an aperture for receiving a 
fastener, such as a bolt, for securing the mounting surface of the tooth 
to the shank plate. The tooth is provided with a lug that extends beyond 
the mounting surface of the tooth for cooperating with a recess formed in 
the shank plate. In this manner, the need for welding a tab to the shank 
plate to cooperate with the tooth and minimize tooth rotation is 
eliminated. 
The lug is configured to snugly fit in the recess so that the lug always is 
sufficiently in contact with the inner wall(s) of the recess to prevent 
relative movement therebetween. In this manner, the lug prevents tooth 
rotation or oscillation about the bolt when the tooth is bolted to the 
plate and the lug is secured in the recess. The lug also prevents the 
tooth from slipping, e.g., sliding laterally, forwardly or rearwardly. 
With the tooth secured against slip and rotational or oscillatory 
movement, it can more effectively dig into the earth being excavated. 
Since the lug restrains the movement of the tooth, slight loosening of the 
bolt does not permit significant movement of the tooth, i.e., movement 
that would render it ineffective. In addition, as the tooth digs into the 
earth, forces placed on the tooth are transferred to the shank plate 
through the lug due to the positive contact between the lug and shank 
plate. This reduces stress transfer through the fastener, thereby 
increasing the life of the fastener. In accordance with the preferred 
embodiment, the lug is tapered to provide the desired snug fit in the 
shank plate recess and prevent relative movement between the lug and shank 
plate, while allowing for manufacturing tolerances. 
According to another aspect of the invention, the proximal portion of the 
tooth includes mounting surfaces on opposite sides thereof and a lug 
extending beyond each surface. In this manner, the tooth can be readily 
reversed by loosening the bolt and removing one lug from the recess, 
turning the tooth over and inserting the other lug into the recess and 
tightening the bolt. 
According to another aspect of the invention, the proximal portion of the 
tooth also is provided with differently oriented mounting surfaces, which 
are adapted for alternate mounting to a shank plate. More specifically, 
the mounting surfaces converge toward the distal portion and form 
different angles with a plane generally bisecting the distal portion. With 
this construction, the attack angle of the tooth can be changed by turning 
the tooth over and alternating the mounting surface secured to the tooth 
holder or shank plate. Thus, a tooth constructed to provide 
interchangeable 40.degree. and 50.degree. attack angles can be used to dig 
soft agricultural soil at a 40.degree. attack angle and then reversed when 
a relatively hard stratum is encountered. 
A further advantageous aspect of the present invention is the provision of 
bolt head seating surfaces in the proximal portion which permit the 
locking bolt to be maintained substantially perpendicular to the tooth so 
that the tooth can be securely fastened to a shank plate. In the preferred 
embodiment, one seating surface is parallel to one of the mounting 
surfaces and the other seating surface is parallel to the other mounting 
surface. 
The above is a brief description of some deficiencies in the prior art and 
advantages of the present invention. Other features, advantages and 
embodiments of the invention will be apparent to those skilled in the art 
from the following description, accompanying drawings and appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the drawings in detail, wherein like numerals indicate like 
elements, FIG. 1 illustrates tooth and shank assemblies 2 and 4 
constructed in accordance with the present invention. Shank assemblies 2 
and 4 are shown secured to flighting 6 which is helically wound around 
auger shaft 8 to convey spoil to the surface of the area being excavated 
as is conventional in the art. In the embodiment illustrated in FIG. 1, 
pilot head 10 also is provided to cut clearance for auger shaft 8. 
Although a four tooth arrangement is shown, which is suitable for 12, 16, 
18, 24 and 30 inch diameter boring heads, for example, other arrangements 
can be used to accommodate these other boring head dimensions as would be 
apparent to one of ordinary skill. 
Shank plate assemblies 2 and 4 generally include shank plates 12 and 14, 
drilling elements or teeth 16, and fasteners 18, which secure the teeth to 
the shank plates. Shank plates 12 and 14 each include a first portion 20, 
21 for securing the shank plate to the flighting and a second portion 22, 
23 to which the teeth are secured. Referring to FIG. 2, first portions 20 
and 21 can be secured to the flighting by welding, as indicated by 
reference numeral 24, for example. Shank plates 14 and 16 differ in the 
arrangement of their tooth mounting holes, which will be discussed in more 
detail below, so that one of the teeth can be angled radially inwardly, as 
shown in FIG. 1, to ensure that clearance is cut for auger shaft 8. Since 
the configuration of each tooth 16 and its attachments to shank plate 12 
or 14 is essentially identical, only a single tooth and its attachment to 
a shank plate will be discussed in detail below. 
Tooth 16 includes a distal portion 26 and a proximal portion 28. Distal 
portion 26 includes top and bottom faces 30 and 32 which terminate in 
digging or cutting end 34. The distal portion can be tapered as is 
conventional in the art and shown in the drawings in which faces 30 and 32 
are angled downwardly in the forward direction toward end 34. Proximal 
portion 28, which is configured for fastening the tooth to the shank 
plate, includes two laterally spaced prongs 36 and 38 which form slot 40 
therebetween. As shown in FIG. 3, slot 40 extends forwardly from the 
proximal ends 42 and 44 of the prongs to wall 46. 
Slot 40 preferably is rectangular in shape with wall 46 being substantially 
planar, as shown in FIGS. 3 and 5, to cooperate with a square shanked 
fastener. That is, fastener 18 preferably is a carriage bolt having a 
square upper shank portion 48, which is dimensioned to fit snugly in slot 
40. The engagement of the square neck 48 with the side edges of slot 40 
prevents the tooth from getting out of alignment with the shank plate and 
prevents relative rotation between fastener 18 and tooth 16. 
Each prong has a top face 50, 52 and a bottom face 54, 56. Each face pair 
50, 52 and 54, 56 preferably forms a substantially flat mounting surface 
58, 60 for mounting the proximal portion of the tooth to a shank plate as 
will be discussed in more detail below. Prongs 36 and 38 also have 
depressions formed therein to form bolt head seating surfaces 62 and 64 
adjacent or around slot 40 (see, e.g., FIGS. 3 and 5). 
In accordance with the present invention, a fastener, such as a bolt and 
nut fastener, and a locking lug which extends from each tooth are used to 
secure each tooth to a respective shank plate. Accordingly, each shank 
plate includes a bolt hole and a lug-receiving recess or through hole for 
each tooth to be mounted thereon. As exemplified in FIG. 3, shank plate 14 
includes bolt hole 70 and lug recess 74. Fastener 18 extends through hole 
70 so that nut 72 can be secured to the threaded end of the fastener to 
lock the proximal portion of tooth 16 against generally planar shank plate 
mounting surface 23. Lug receiving recess or hole 74 receives either lug 
66 or 68 depending on the position of tooth 16. 
Referring to FIG. 6, prong 36 includes lug 66 and prong 38 includes lug 68. 
Each lug extends beyond and generally perpendicular to the portion of the 
mounting surface 58, 60 adjacent thereto. When one of those mounting 
surfaces 58, 60 is seated against the corresponding mounting surface of 
the shank plate to mount the proximal portion of the tooth to the shank 
plate, the tooth and shank plate mounting surfaces abut one another while 
the lug extends into the lug recess such as recess 74. Specifically, lug 
66 extends beyond mounting surface 60 and lug 68 extends beyond mounting 
surface 58. Lugs 66 and 68 each have a configuration generally 
corresponding to that of recess 74 and are dimensioned to snugly fit in 
that recess so that the lug always is sufficiently in contact with an 
inner wall(s) of the recess to prevent relative movement therebetween and 
transfer forces from the tooth to the shank plate. In this way, stress 
transfer through the bolt is minimized, thereby enhancing the life of 
fastener 18. That is, the interlock between the lug and the shank plate 
reduces the load on the fastener. 
As shown in the drawings, each lug preferably is tapered to provide the 
desired fit within a respective recess 74. Although a lug having a 
generally rectangular sectional configuration is shown, it should be 
understood that other configurations can be used without departing from 
the scope of the present invention. For example, the lug can have a 
circular, triangular, pentagonal or hexagonal cross section. 
Referring to FIGS. 3-6, the preferred arrangement of locking lugs for a 
reversible tooth is shown. Specifically, locking lug 66 extends from the 
bottom of prong 36, while locking lug 68 extends from the top of prong 38. 
Thus, when tooth 16 is positioned with top face 30 of the tooth facing 
upwardly as shown in FIG. 3, lug 66 cooperates with recess 74. However, 
when the tooth is reversed such that bottom face 32 of the tooth faces 
upwardly, lug 68 cooperates with recess 74. Thus, the configuration of 
lugs 66 and 68 preferably are essentially identical. 
Referring to FIGS. 3, 4, and 7, the mechanism for varying the attack angle 
of the tooth will be described. As shown in the drawings, mounting surface 
60 is generally coplanar with bottom face 32 of distal portion 26, but 
mounting surface 58 is not coplanar with top face 30 of distal portion 26. 
That is, mounting surfaces 58 and 60 are substantially nonparallel. In 
this manner, the attack angle, designated with reference character 
.alpha., can be changed when the position of the mounting surfaces are 
alternated and the tooth is reversed from the position shown in FIG. 7A to 
that shown in FIG. 7B. In the preferred embodiment, the mounting surface 
58 forms an angle with mounting surface 60 of at least about 5.degree., 
which results in a corresponding change in .alpha. of at least about 
5.degree.. In other words, when the tooth is reversed from the position 
shown in FIG. 7A to that shown in FIG. 7B, the angle formed between a 
plane 76 that bisects the top and bottom faces of distal portion 26 and a 
plane extending transversely through the shank plate and parallel to the 
longitudinal axis of fastener 18 as designated by reference numeral 78, 
for example, changes by an amount equal to the angle formed between the 
mounting surfaces 58 and 60. 
The orientation of the bolt seating surfaces constitutes another important 
aspect of the invention. Specifically, bolt seating surface 62 is 
substantially parallel to tooth mounting surface 60, while bolt seating 
surface 64 is substantially parallel to tooth mounting surface 58. With 
this configuration, the bolt is maintained essentially perpendicular to 
the portion of the shank plate to which the tooth is mounted and the 
contact area between the bolt head and tooth and the nut and shank plate 
is maximized to enhance the securement of the tooth to the shank plate. 
The above is a detailed description of a particular embodiment of the 
invention. It is recognized that departures from the disclosed embodiment 
may be made within the scope of the invention and that obvious 
modifications will occur to a person skilled in the art. The full scope of 
the invention is set out in the claims that follow and their equivalents. 
Accordingly, the claims and specification should not be construed to 
unduly narrow the full scope of protection to which the invention is 
entitled.