US3206876A

US3206876A - Mobile ditching machine with boom type digger having t-shaped buckets

Info

Publication number: US3206876A
Application number: US258345A
Authority: US
Inventors: Vincent S Penote; Hans L Preu
Original assignee: Cleveland Trencher Co
Current assignee: Cleveland Trencher Co
Priority date: 1963-02-13
Filing date: 1963-02-13
Publication date: 1965-09-21
Anticipated expiration: 1982-09-21
Also published as: DE1484637C3; DE1484637A1; GB1044403A; DE1484637B2

Description

Sept. 21, 1965 v. s. PENOTE ETAL 3,206,875

MOBILE DITCHING MACHINE WITH BOOM TYPE DIGGER HAVING T-SHAPED BUCKETS Filed Feb. 15, 1963 4 Sheets-Sheet 1 Q m g s3 \1 s w m D O o 4 5: o o V o o a O o o O O o o o c an j o o m x O Q I o Q 5? '3 o w v O a \Y/ Q Fig.

INVENTORS VINCENT s. PENOTE BY HANS L.PREU

g le 71 1 V7 ATTORNEYS Sept. 21, 1965 V. s. PENOTE ETAL MOBILE DITCHING MACHINE WITH BOOM TYPE DIGGER HAVING T-SHAPED BUCKETS Filed Feb. 13, 1963 GGGGQ fi 4 Sheets-Sheet 2 IN VENTORS VINCENT S. PENOTE y HANS L. PREU ATTORNEYS Sept. 21, 1965 v. s. PENOTE ETAL 3,206,876

MOBILE DITCHING MACHINE WITH BOOM TYPE DIGGER HAVING T-SHAPED BUCKETS Filed Feb. 15, 1965 4 Sheets-Sheet 3 1N VENTORS VINCENT S. PENOTE BY HANS L. PREU ATTORNE S Sept. 21, 1965 v. s. PENOTE ETAL 3,206,376

MOBILE DITCHING MACHINE WITH BOOM TYPE DIGGER HAVING T-SHAPED BUCKETS Filed Feb. 13, 1963 4 Sheets-Sheet 4 6 62 \

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42 ,58 ,I 62 Q 40 68 3/66 32 60 12 88 56a 74 IN VENTORS VINCENT S. PENOTE BY HANS L. PREU ATTORNEYS United States Patent 3,206,876 MOBILE DITCHING MACHINE WITH BOOM TYPE DIGGER HAVING T-SHAPED BUCKETS Vincent S. Penote, Shaker Heights, and Hans L. Preu,

Wicklifie, Ohio, assignors to The Cleveland Trencher Company, Cleveland, Ohio, a corporation of Ohio Filed Feb. 13, 1963, Ser. No. 258,345 8 Claims. (Cl. 37-86) This invention relates in general to a mobile ditching machine having an endless, bucket equipped digging unit of the ladder type, and which may be used to advantage in connection with the excavation of trenches, for such purposes as utility service lines, such as gas, water, or sewer lines, and the like.

In the copending United States patent application of Vincent S. Penote et al., Serial No. 239,548, filed November 23, 1962, there is disclosed a mobile ditching machine having a ladder type digging unit of the general classification with which the instant invention is concerned. In such ditching machine arrangement of said copending patent application, there is provided a plate-like bucket cleaner element disposed generally adjacent the upper end of the digging unit, which plate-like bucket cleaner element includes an opening therein through which the rooter tooth equipped buckets on the digging line are adapted to move, as the buckets move around the upper, rotatable sprocket or mounting member of the digging unit. Such bucket cleaner is adapted to scrape excavated material in the buckets, from the latter, and such excavated material is adapted to fall downwardly to be carried into a spoil conveying mechanism extending transversely of the ditching machine, and which spoil mechanism moves the excavated material transversely of the ditching machine to a side of the excavation.

The present invention provides a novel arrangement of ladder type digging unit for a ditching machine wherein the bucket elements of the digging unit, and the associated rooter teeth, are so aligned or disposed as to form a configuration which in side elevation is more nearly that of a segment of a circle, with the center of curvature corresponding to the axis of rotation of the upper sprocket or mounting member of the digging unit. In this way, a more complete cleaning operation of the buckets by the aforementioned bucket cleaner is possible. Moreover, the lower end of the ladder type digging unit is so constructed and arranged that the bucket is caused to somewhat lag the digging line or link chain to which the buckets are attached, as the buckets move around the lower rotatable supporting member of the digging unit, thus providing adequate clearance in the material cut by the rooter teeth, for the bucket spade portions and associated teeth.

Accordingly, an object of the invention is to provide a novel arrangement of ditching or trenching machine.

Another object of the invention is to provide a mobile ditching machine having a novel arrangement of bucket equipped, ladder type digging unit thereon.

A more specific object of the invention is to provide an endless, bucket equipped, ladder type digging unit for a ditching machine, wherein the forward or spade portions of the buckets are of arcuate configuration, in side elevation, and are attached to the link chain digging line by means of a generally centrally disposed web portion, and wherein the spade portions have rooter teeth mounted on the leading edges thereof, with such rooter teeth being disposed generally in alignment with the respective bucket spade portion, to define a more or less continuation of the arcuate configuration of the spade portion, and with the center of curvature of the spade portions being disposed substantially concentrically with the axis of rotation of ice the mounting drive sprocket member for the digging line.

Another specific object of the invention is to provide a digging unit of the latter discussed type, wherein means is provided on the rotatable mounting at the lower end of the digging unit, for enabling the buckets and associated rooter teeth to lag the mounting digging line chain as they move around the lower mounting member, for increasing the clearance between the outer side of the spade portions of the buckets and the surface of the cut in the ground made by the rooter teeth.

Other objects and advantages of the invention will be apparent from the following description taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side elevational, partially broken, generally diagrammatic view of a trenching machine embodying the digging unit of the instant invention;

FIG. 2 is a fragmentary, generally perspective View of the digging line boom and associated bucket cleaner of the trencher construction;

FIG. 3 is a fragmentary side elevational view of the digging unit, showing a portion of the digging line chain and associated buckets of the trenching machine, as they pass around the upper rotatable mounting member of the digging unit;

FIG. 4 is a fragmentary, side elevational view of the lower end of the digging unit of the invention, and showing the configuration of the lower support or idler sprocket member, which permits lagging of the buckets with respect to their mounting digging line chain links, thereby aiding in providing clearance for the bucket spade portions and associated rooter teeth during movement of the buckets and digging line chain about the lower support member;

FIG. 5 is a generally front elevational View of one of the buckets and associated link chain digging line of the digging unit, and taken generally along the plane of line 55 of FIG. 3, looking in the direction of the arrows.

Referring now again to the drawings, the trenching machine may broadly comprise a chassis frame 10 supported on spaced, endless treads or tracks 12 of conventional, well known construction. Mounted on the chassis at the forward end thereof, may be an internal combustion motor 14. A machine operators Work station 16 may be disposed adjacent motor 14, and supported adjacent the rearward end of the chassis 10 in generally counterbalancing relation to engine 14, may be an endless digging unit 18. A pair of transversely spaced wheels 20 may be mounted adjacent the forward end of the chassis frame, and which wheels in the embodiment illustrated, are pivoted to the chassis frame, as at 21, for raising and lowering movement, whereby the wheels may be lowered either to the phantom line illustrated, which would lift the forward ends of tracks 12 off the ground, or the wheels 20 may be pivotally raised to the full line position shown, which is the storage position of the wheels. Such wheels 20 provide for converting the trenching machine into a trailer-like arrangement for rapid portability of the same on roads and the like, and yet a machine wherein the endless tracks can be readily utilized for operating during conventional digging.

The bucket equipped digging unit 18 may be pivoted to the machine chassis as at 26, and thus may be swung from a raised inoperative position wherein the digging unit is disposed above ground level, to a lowered op erative digging .position, and vice versa. Motor unit 30 may be provided for so swinging the digging unit in a generally vertical plane and about axis 26.

Digging unit 18 may comprise an adjustable boom 32, which may be of generally elongated box-like construction (FIG. 2) and which may include main section 32a on which may be rotatably mounted an upper drive sprocket member 34, and a lower section 32b which may be adjustably mounted for lengthwise movement with respect to the main section 32a, and as by means of bolt and nut fastener assembly 36, and which lower section 3217 rotatably mounts an idler sprocket member 38 (FIG, 4) thereon. Strung around the upper and lower

rotatable members

34, 38 of the digging unit is an endless digging line, in the form of link chain 40 to which are attached an articulated type of bucket 42 which will be hereinafter described in greater detail.

A conveyor mechanism 44 may be provided on the machine for transferring the dug material discharged by the buckets 42, to a side of the excavation, and in the embodiment illustrated, this mechanism comprises a rotata'ble screw member 46 driven from a sprocket 48 attached by shaft '50 to the upper, drive sprocket 34 of the digging unit. Sprocket 34 may be driven by shaft 50 which in turn may be driven by any suitable means, such as for instance rotary fluid powered motor unit 52 suitably coupled to shaft 50. Screw member 46 is adapted to receive material from the buckets 42 as the latter move around the upper drive sprocket 34, and move such material laterally to a side of the excavation.

The digging unit maybe provided with plate-like scraper or bucket cleaner member 54, which has a generally T-shaped opening 54a (FIG. 2) therethrough, through "which is adapted to pass the buckets. Reference may be had to the aforementioned pending patent application Serial No. 239,548, for a more detailed description of the afore discussed ditching machine, includ ing the bucket cleaner 54.

Referring now to FIGS. 3, .4 and 5, it will be seen that each bucket in the instant arrangement may comprise a pair of back-up

plates

56, 56a connected to alternate links of the digging line chain 40. The digging line chain comprises

links

58, 60 pivotally interconnected as at 62. The back-

up plates

56, 56a may be attached by any suitable means to the respective links, and as for instance by means of Welds. Each of the plates '56, 56a at its tail end is bent inwardly or downwardly as at- 66, and is provided with a slot 66a therein for receiving the associated link without interference when the chain links are in a linear or aligned condition, during their travel about the upper and lower

rotatable members

34, 38 of the digging unit. The aforementioned notch or slot 66a in each of the plates also provides for movement of any accumulation of excavated material in links 60, outwardly through such notches, by virtue of the teeth of the

sprocket wheels

34, 38 which extend into links 60.

Each plate 56 is provided with a generally central web 68 which web is of the generally L-shaped configuration illustrated, initially extending diagonally outwardly and rearwardly from the associated plate 56 and then turning relatively sharply to extend generally parallel with the associated plate 56a in the linear condition of

plates

56, 56a. Each Web 68 at its rearward edge supports or carries a generally curved plate 70 of substantially the

same widthas plates

56, 56a. This plate 70 commences substantially at the outer edge 72 of the Web 68 and extends rea-rwardly and curves inwardly in a generally arcuate configuration, with the center of curvature of said arcuate configuration being generally the .axis of shaft 50 of the upper drive sprocket member 34 of the digging unit. As can be best seen in FIG. 3, this curved plate 70 terminates generally rearwardly of the rearwardrnost back plate 56a of the respective bucket, and may engage the central web of the. next adjacent bucket in the linear or straight run stretches of the digging line, and thus aid in maintaining the stability of the buckets as they move upwardly and the rooter teeth 74 thereof cut into the ground X (FIG. 4).

Accordingly, the plate 70 forms the front or spade portion of the respective bucket with the back of the bucket being formed by the

paired plates

56, 56a of the respective chain links, and with the center web 68 supporting the spade portion 70 of the bucket, the latter thus being open on its sides. The rooter tooth 74 on the leading end of each spade portion 70 may be suitably releasably attached as by means of a sleeve or socket 78 mounted on the outer surface of the respective spade portion of the bucket. Such socket may coact in wedging relation with the tooth, and the latter may also be provided with a boss 78a thereon for aiding in retaining the tooth in the socket. Such a rooter element, as best shown in FIG. 3, is of .generally flattened, platel-ike shape and this provides a generally continuation of the arcuate interior surface 80 of the respective bucket. Accordingly, as the buckets pass around the upper drive sprocket member 34 and through the opening 54a in the plate bucket cleaner 54, effective cleaning of each bucket occurs, since the finger portions 82 of the bucket cleaner extend from the center web 68 to each side of the bucket, and substantially throughout the generally arcuate path defined by the interior configuration of the bucket spade portion 70 and associated rooter tooth as they move around the axis of rotation of sprocket 34, and scrape out any material therein. Such scraped out material falls downwardly to be carried forward by the forward movement of the wings 86 (FIG. 2) on the boom 32 during forward movement of the excavating machine, and into the spoil screw 46, from whence it is moved laterally to a side of the excavation.

Referring now to the lower portion of the digging unit 18, and more specifically the idler sprocket member 38 thereof (FIG. 4) such idler sprocket member has-a novel configuration for enabling the, spade portion 70 of the bucket to lag the mounting digging line chain 40 when coming around such idler sprocket, thus providing a substantial clearance P between the outer surfaces of the tooth and associated spade portion of the bucket, and the confronting surface of the ground X being excavated. Sprocket 38 has generally flat surfaces 88 thereon disposed intermediate the teeth 89 which enable the chain link 58 mounting back plate 56, and the .next adjacent shorter link 60, to be disposed in a generally linear relationship shown in FIG. 4, as the links and associated bucket move around the axis of rotation 90 with the idler. sprocket, during upward movement of the digging line to excavate the material. As can be seen, the flat portions 88 of the sprocket provide for the generally linear relationship between

links

58, 60 associated with the center web 68, as compared to the angular relationship of the next adjacent set of

links

58, 60 not associated with the central web member. The peripheral edge of the sprocket may also be recessed or cut away as as 92 following the respective generally flat planar surface 88, so as to provide clearance between the respective cross piece 62 pivotally connecting the pair of

links

58, 60 associated with center web 68, together, and thereby insuring that such links are maintained in the generally linear relationship illustrated, which relationship as aforementioned provides for the clearance between the surface of the excavation and the respective bucket as it moves around the idler sprocket 38.

From the foregoing discussion and accompanying drawings, it will be seen that the invention provides a novel bucket equipped digging unit of the ladder type for a trenching machine, and one wherein the cleaning operation on the buckets of the digging unit is much more effectively performed as compared to heretofore known arrangements, for more efficient and effective use of the trenching machine, and a novel construction for establishing adequate clearance between the buckets and the excavation, as the buckets move around the lower end of the digging unit.

The terms and expressions which have been used are used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of any of the features shown or described, or portions thereof, and it is recognized that various modifications are possible within the scope of the invention claimed.

We claim:

1. In a mobile trenching machine comprising a support, an endless digging unit mounted on said support, said digging unit comprising an endless, link digging line and buckets secured to said line for digging operations upon movement of said line, upper and lower rotatable mounting members about which the bucket equipped line is looped, at least said upper member being a toothed circular sprocket, each bucket comprising a plurality of back plates disposed in generally aligned relation on said line, each of said back plates being secured to an alternate link of said line for articulated movement of said plates with respect to one another as they move about said upper sprocket on said line, each back plate coacting with a pair of adjacent links, with said back plates forming an articulated inner wall for the respective bucket, each bucket comprising an outer spade portion supported by a centrally disposed web carried by the forwardmost of said back plates, and rooter tooth means mounted on said spade portion and projecting forwardly therefrom, said spade portion having an interior surface of generally arcuate configuration in side elevation, with the center of curvature of said surface, as the respective bucket moves in an arcuate path about said upper sprocket, coinciding with the axis of rotation of said upper sprocket, said rooter tooth means providing a generally linear extension of said surface on the respective bucket, and bucket cleaner means mounted in fixed relation on said machine adjacent said upper sprocket and extending into the vicinity of said arcuate path, said cleaner means being adapted to extend into the interior of said buckets in close proximity to said surface and said tooth means as the buckets pass about said upper sprocket, for forcing spoil therefrom said bucket cleaner means including a plate-like member having an elongated slot extending from one end thereof and an opening adjacent the top thereof to accommodate movement of the bucket therethrough, defining laterally spaced leg sections, said spade portion and web of each bucket being adapted to pass through said slots with said leg sections disposed on opposite sides of said web.

2. A mobile trenching machine in accordance with claim 1 wherein said outer spade portion is supported on said forwardmost back plate by a central web projecting outwardly and rearwardly therefrom, said spade portion and attached rooter tooth means being disposed rearward- 1y of said forwardmost back plate in the linear stretches of said digging line.

3. A mobile trenching machine in accordance with claim 1, wherein said lower mounting member is a toothed sprocket about which said digging line travels, said toothed sprocket being of a generally circular configuration but including linear sections disposed intermediate and inwardly of the teeth defining said sprocket to cause the links of said chain associated with the forwardmost of said back plates to be disposed in generally linear relationship as they move about said lower toothed sprocket to permit inward movement of the respective buckets toward the axis of rotation of said lower toothed sprocket thereby increasing the clearance between said spade portion of each bucket and the defining surface of the excavation.

4. In a mobile trenching machine comprising a support, a ladder-type digging unit including a boom pivoted to said support for swinging movement in a generally vertical plane, said digging unit comprising an endless link chain and buckets secured in spaced relation to the chain for digging operations upon lengthwise movement of said chain, upper and lower sprocket members rotatably mounted on said boom and about which said bucket equipped chain is looped, means for driving one of said sprocket members and thus causing said lengthwise movement of the chain, each of said buckets comprising a pair of back plates disposed in generally aligned relation on the chain, each of the back plates being secured to an alternate link of said chain and providing for articulated move ment of said plates with respect to one another, in the movement of the chain about said sprocket members, each of said plates coacting with a pair of adjacent chain links, with said pair of plates forming an articulated inner wall for the respective bucket, each bucket comprising a generally vertically oriented Web secured generally centrally of the forwardmost of the back plates and extending generally lengthwise thereof and rearwardly into overlapping relation with the rearwardmost of the back plates, an outer spade portion secured to said web and curving rearwardly and inwardly to terminate behind the rear boundary of said rearwardmost back plate, rooter tooth means mounted on said spade portion and extending forwardly therefrom, said buckets being open on the sides thereof with said spade portion having an interior surface of generally arcuate configuration in side elevation, the center of curvature of said surface of the respective bucket as the latter moves in an arcuate path about said upper sprocket member coinciding with the axis of rotation of said upper sprocket member, said rooter tooth means providing a generally linear extension of said surface on the respective bucket, bucket cleaner means mounted in fixed relation on said boom above said axis of rotation and extending into the vicinity of said arcuate path of movement of the respective bucket, said cleaner means being adapted to extend into both sides of the opensided buckets in close proximity to said surface and asso ciated rooter tooth means, as the buckets pass about said upper sprocket member, for effectively forcing any spoil therefrom, and wherein the lower sprocket member is a toothed sprocket about which said digging line travels, said toothed sprocket being of a generally circular configuration but including linear sections disposed intermediate and inwardly of the teeth on said sprocket to cause the links of said chain associated with the forwardmost of said back plates to be disposed in generally linear relation as they move about said lower sprocket to permit inward movement of the respective bucket toward the axis of rotation of said lower toothed sprocket thereby increasing the clearance between said spade portion of each bucket and the defining surface of the excavation.

5. In a mobile trenching machine comprising a support, a ladder-type digging unit including a boom pivoted to said support for swinging movement in a generally vertical plane, said digging unit comprising an endless, link chain and buckets secured to the chain for digging operations upon lengthwise movement of said chain, upper and lower sprocket members rotatably mounted on said boom and about which said bucket equipped chain is looped, means for driving said upper sprocket member and thus causing said lengthwise movement of said chain, each bucket comprising a pair of back plates disposed in generally aligned relation on said chain, each of said back plates being secured to an alternate link of said chain and providing for articulated movement of said plates with respect to one another in the movement of said chain about said upper sprocket member, each of said back plates coacting with a pair of adjacent links of said chain, with said pair of back plates forming an articulated inner wall for the respective bucket, each bucket comprising a generally vertically oriented web secured generally centrally of the forwardmost of said back plates and extending generally lengthwise thereof and rearwardly into overlapping relation with the rearwardmost of said back plates, an outer spade portion secured to said Web in outwardly spaced relation to said rearwardmost back plate and curving rearwardly and inwardly to terminate behind the rear boundary of said rearwardmost back plate, a flat plate-like rooter tooth mounted on said spade portion and extending forwardly therefrom, said buckets being open on the side thereof with said spade portion having an interior surface of generally arcuate configuration in side elevation, the center of curvature of said surface, as the respective bucket moves in an arcuate path about said upper sprocket member, coinciding with the axis of rotation of said upper sprocket member, said rooter tooth providing a generally linear extension of said surface on the respective bucket, and bucket cleaner means mounted in fixed relation on said boom and above said axis of rotation, said bucket cleaner means extending into the vicinity of said arcuate path and being adapted to extend into both sides of the open sided bucket in close proximity to said surface and associated rooter tooth, as the buckets pass about said upper sprocket member, for etfectively forcing any spoil therefrom, and wherein said bucket cleaner means comprises a plate-like member having a generally T-shaped slot therethrough, defining laterally spaced leg section's, said spade portion and Web of each bucket being adapted to pass through said slot with said leg sections disposed on opposite sides of said web.

6. A mobile trenching machine in accordance with claim wherein the trailing end of each of said back plates is bent inwardly toward the chain, and each of said trailing ends has a slot therein for receiving in non-interfering relation the chain links in the linear stretches of said chain.

7. A mobile trenching machine in accordance with claim 5, wherein the lower sprocket member is a toothed sprocket about which said digging line travels, said toothed sprocket being of a generally circular configuration but including linear sections disposed intermediate and inwardly of the teeth defining said sprocket to cause the links of said chain associated with the forwardmost of said backplates to be disposed in generally linear relationship as they move about said lower toothed sprocket to permit inward movement of the respective buckets to- Ward the axis of rotation of said lower toothed sprocket tion of each bucket and the defining surface of the excavation.

8. In a mobile trenching machine comprising a support, a ladder-type digging unit including a boom pivoted to said support for swinging movement in a generally vertical plane, said digging unit comprising an endless, link chain and bucket secured to the chain for digging operation upon lengthwise movement of said chain, upper and lower sprocket members rotatably mounted on said boom and about which said bucket equipped chain is looped, means for driving said upper sprocket member and thus causing said lengthwise movement of said chain, and said lower sprocket member being a toothed sprocket about which said digging line travels, said toothed sprocket being of a generally circular configuration but including linear sections disposed intermediate and inwardly of the teeth defining said toothed sprocket to cause the links of said chain to be disposed in generally linear relation as they move about said lower toothed sprocket to permit inward movement of the respective buckets toward the axis of rotation of said lower toothed sprocket thereby increasing the clearance between each bucket and the defining surface of the excavation.

References Cited by the Examiner UNITED STATES PATENTS 883,821 4/08 Monahan 3790 1,287,675' 12/18 Greimann 379'0 1,484,841 2/24 Monahan et al 198144 X 1,799,204 4/31 Wily 37-141 X 1,802,106 4/31 Bosworth 37l4l 2,063,858 12/36 Stires 37-141 2,599,778 6/52 Przybylski 3'79O 2,667,709 2/54 Askue 37191 X BENJAMIN, HERSH, Primary Examiner.

Claims

1. IN A MOBILE TRENCHING MACHINE COMPRISING A SUPPORT AN ENDLESS DIGGING UNIT MOUNTED ON SAID SUPPORT, SAID DIGGING UNIT COMPRISING AN ENDLESS, LINK DIGGING LINE AND BUCKETS SECURED TO SAID LINE FOR DIGGING OPERATIONS OPON MOVEMENT OF SAID LINE, UPPER AND LOWER ROTATABLE MOUNTING MEMBERS ABOUT WHICH THE BUCKET EQUIPPED LINE IS LOOPED, AT LEAST SAID UPPER MEMBER BEING A TOOTHED CIRCULAR SPROCKET, EACH BUCKET COMPRISING A PLURALITY OF BACK PLATES DISPOSED IN GENERALLY ALIGNED RELATION ON SAID LINE, EACH OF SAID BACK PLATES BEING SECURED TO AN ALTERNATE LINK OF SAID LINE FOR ARTICULATED MOVEMENT OF SAID PLATES WITH RESPECT TO ONE ANOTHER AS THEY MOVE ABOUT SAID UPPER SPROCKET ON SAID LINE, EACH BACK PLATE COACTING WITH A PAIR OF ADJACENT LINKS, WITH SAID BACK PLATES FORMING AN ARTICULATED INNER WALL FOR THE RESPECTIVE BUCKET, EACH BUCKET COMPRISING AN OUTER SPADE PORTION SUPPORTED BY A CENTRALLY DISPOSED WEB CARRIED BY THE FORWARDMOST OF SAID BACK PLATES, AND ROOTER TOOTH MEANS MOUNTED ON SAID SPADE PORTION AND PROJECTING FORWARDLY THEREFORM, SAID SPADE PORTION HAVING AN INTERIOR SURFACE OF GENERALLY ARCUATE CONFIGURATION IN SIDE ELEVATION, WITH THE CENTER OF CURVATURE OF SAID SURFACE, AS THE RESPECTIVE BUCKET MOVES IN AN ARUCATE PATH ABOUT SAID UPPER SPROCKET, COINCIDING WITH THE AXIS OF ROTATION OF SAID UPPER SPROCKET, SAID ROOTER TOOTH MEANS PROVIDING A GENERALLY LINEAR EXTENSION OF SAID