WO2000055434A1

WO2000055434A1 - Excavator tool and bucket

Info

Publication number: WO2000055434A1
Application number: PCT/GB2000/000993
Authority: WO
Inventors: Andrew Dodd; Siu Keung Lee; Mark Shearsby
Original assignee: Lee Shearsby Dodd Ltd.
Priority date: 1999-03-17
Filing date: 2000-03-16
Publication date: 2000-09-21
Also published as: AU3305700A; GB2347921A; GB9906201D0

Abstract

There is described an excavator tool (9) mounted to an arm (6) of an excavator for penetrating paving or asphalt without the need first to break up the paved surface. The excavator tool (9) comprises mounting means for pivotally mounting the tool to the arm for pivoting movement about a pivot axis (10), means for rotating the tool relative to the arm (6) about the pivot axis, a convex surface (22; 30; 70) arranged substantially concentrically with the pivot axis, a number of cutting elements (28; 48; 62; 75) arranged on the convex surface, the cutting elements having respective cutting tips arranged to project radially from the convex surface. In an advantageous embodiment, the excavator tool (9) is an excavator bucket with cutting elements (28) on its sole plate (22). An attachment for a conventional bucket to convert it to an excavator tool is also described.

Description

Excavator Tool and Bucket

The present invention relates to mechanical excavators, and is principally concerned with the provision of a tool or bucket for a mechanical excavator for use in trenching. More particularly, the invention relates to an excavator tool capable of penetrating a road surface.

Many civil engineering contracts call for excavation of trenches or holes in roadways, or other paved areas. The conventional method of digging trenches and holes in paved roads is expensive both in terms of manpower and plant required. The current process involves three distinct stages, as follows: The edges of the opening to be formed are cut into the roadway using a diamond-bladed saw, to produce a slot or kerf approximately 5mm wide, and penetrating through the asphalt or concrete paving. Such road saws are conventionally self-contained tools powered by a petrol engine. The use of such saws generates large quantities of dust, due to the high speed of the cutting blade, and protective clothing is normally required for the operative. The environmental nuisance caused by the dust is also considerable, and the blades are expensive and have a short working life.

The second stage involves the use of a road drill or jackhammer to break up the asphalt or concrete paving between the kerfs, so that the continuity of the paving over the area to be excavated is destroyed. The conventional road drill is a pneumatic drill requiring a compressed air supply, usually provided by a trailer- mounted compressor unit powered by a diesel or petrol engine. The process of breaking up the paving requires the site to be well clear of any public areas, and substantial noise pollution is generated.

The third stage involves removal of the now broken paving and its underlying strata to the required depth of the hole or tench. This is usually achieved by means of an excavator having a bucket whose width is slightly smaller than or equal to that of the trench to be formed.

The conventional trench digging process thus involves three distinct operations requiring different equipment and different skills on the part of the operatives . The operations also involve the use of more operatives than are strictly necessary to operate the equipment due to the logistical difficulties in transporting and deploying the equipment on site.

For example, vehicles are required to transport the road saw, drill and compressor, and possibly also the excavator. Manhandling the equipment on site, and maintenance of equipment by replacing worn blades and bits, generally requires two or more operatives permanently employed, even for digging a narrow trench in a roadway for pipe or cable laying. The present invention sets out to reduce the dust and noise pollution involved in forming a trench or hole in a roadway, and to shorten the time taken and resources required for the job both in terms of plant and manpower.

The present invention seeks to provide an excavator tool for use with a mechanical excavator, and an excavating method, which will enable a trench or hole to be dug in a paved roadway by means of the mechanical excavator alone, dispensing with the need to saw and break up the paved surface prior to excavation. A further objective of the present invention is to provide a bucket for attachment to a mechanical excavator, to provide the excavator with the capability of breaking and excavating a paved roadway surface.

A yet further objective of the present invention is to provide an attachment for a conventional excavator bucket which will enable the excavator bucket to be used to form openings in a paved roadway.

Embodiments of the present invention will be described in detail, with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of a conventional mechanical excavator fitted with a bucket according to the invention;

Figure 2 is a sectional view of an excavator bucket according to an embodiment of the present invention;

Figure 3 is an enlarged sectional view of a cutting tooth;

Figure 4 is an exploded perspective view of the cutting tooth; Figure 5a and Figure 5b show alternative patterns of fixing the cutting teeth to the sole plate of the excavator bucket;

Figure 6 is a sectional side view of a further embodiment of the invention, comprising a conventional excavator bucket and a detachable sole plate assembly; Figure 7 is a sectional view of an alternative detachable sole plate assembly;

Figure 8 is a partially cut away perspective view of the sole plate assembly of Figure 7; Figure 9 is an exploded view of an alternative cutting tooth and an alternative attachment to the sole plate of an excavator bucket;

Figure 10 is an exploded perspective view of a double-acting cutting tooth for bidirectional cutting; and

Figure 11 is a perspective view of a further embodiment of the invention, comprising an excavator tool .

Referring now to the drawings, the mechanical excavator seen in Figure 1 comprises a tracked base 1, which supports a body 2 which is rotatable on the base 1 about a vertical axis for slewing the excavator body. The body 2 comprises a driver's cab 2a and an engine compartment 26 housing the prime mover, and a hydraulic pump and controls for providing hydraulic fluid to drive motors associated with the tracks, and to actuators or rams to be described below. Mounted on the body is a boom 3, which is pivotable about a horizontal axis 4 by means of one or more boom rams 5 mounted between the boom 3 and the body 2.

At the end of the boom 3 remote from the body 2, an arm 6 is mounted to the boom 3 at a pivot 7 for pivoting movement about a horizontal axis . Relative movement between the arm 6 and the boom 3 is controlled by an arm ram 8 connected between an end of the arm 6 and the boom 3.

At the lower end of the arm 6 as seen in the drawing, a bucket 9 is pivotally attached to the end of the arm 6 for pivoting movement about a horizontal pivot axis 10. The bucket 9 has a generally arcuate sole plate

11 concentric with the pivot axis 10, and a cutting edge

12 and open side 13 facing towards the body 2 of the excavator.

A bucket ram 14 is connected to the arm 6 and to a second pivot 15 of the bucket 9. Extension of the bucket ram 14 causes the excavator bucket 9 to move (as seen in the drawing) in an anti-clockwise direction about the pivot axis 10. Likewise, extension of the arm ram 8 causes the arm 6 to rotate in an anti-clockwise direction about the pivot 7, moving the bucket 9 towards the body 2. Extension of the boom ram 5 causes the boom 3 to rotate in a clockwise direction, raising the arm 6 and bucket 9. By a combination of extensions and contractions of the boom ram 5, the arm ram 8 and the bucket ram 14, the operator can cause the cutting edge 12 of the bucket to be drawn towards the body 2 through earth or loosened paving material so that the material enters the bucket through the open side 13. Simultaneously extending the bucket ram 14, arm ram 8, and boom ram 5, the bucket is lifted and may be positioned over a spoil heap or a removal vehicle by slewing the body 2. Retraction of the bucket ram 14 then rotates the bucket clockwise as seen in Figure 1 to tip the spoil from the bucket 9 on to the spoil heap or into the removal vehicle. Particularly in smaller excavators, such as the type generally referred to as a "mini-digger", the weight of the machine and the power available to extend and contract the rams is insufficient to drive the cutting edge 12 of the bucket through an asphalt paved surface in order to cut a trench. Unacceptably high loadings are placed on the bearings at the arm and boom pivots, and if the bucket is used as a hammer to drive the edge 12 through an asphalt surface, impact loadings can cause failure of the arm, boom or bucket.

In order to provide the excavator with the ability to penetrate a paved surface, but avoid the heavy impact loadings on the machinery described above, an embodiment of the present invention provides an excavator bucket for use with a conventional excavator, the bucket being provided with cutting teeth on its sole plate.

An excavator bucket according to a first embodiment of the present invention is seen in a sectional side view in Figure 2. The excavator bucket comprises two side plates 20, a back plate 21, a sole plate 22 and a top plate 23. Extending upwardly from the top plate 23 are a pair of mounting plates 24 for attaching the bucket to the end of an arm 6 of an excavator by means of a pivot pin (not shown) . The mounting plates 24 are provided with two spaced paraxial bearing bores 25 and 26, the bore 25 accepting the pivot pin 10 to connect the bucket to the arm 6 of an excavator. Bearing bore 26 receives a second pivot pin attached to a linkage connected with the bucket ram 14, in order to effect pivoting movement of the bucket about the pivot pin 10 housed in bearing bore 25. The sole plate 22 of the bucket has a leading edge 27, whose distance from the centre of bearing bore 25 is R_L . The sole plate 22 is curved or cranked towards the bearing bore 25 immediately behind the leading edge 27, so that the main part of the sole plate 22 is in an arcuate plane generally concentric with the bearing bore 25, and spaced from the bearing bore 25 by a distance R_s . Attached to the central region of the sole plate 22 and extending downwardly therefrom (as seen in Figure 2) are a plurality of cutting elements generally indicated by 28. The cutting elements 28 are shown in greater detail in Figures 3 and 4. Referring now to Figure 3 , the cutting element 28 comprises a generally "L" shaped body 29 which is attached to the sole plate 22 for example by welding. Alternatively, sole plate 22 may be formed with bores through which bolts can pass to secure the body 29 to the sole plate 22. The upper part 29a of the body 29 extends generally perpendicularly from the sole plate 22, and the lower part 29b extends generally parallel to the sole plate 22. Although the upper part 29a and the lower part 29b are shown extending at right angles to each other, it is to be understood that an obtuse angle may be made between the upper and lower parts of the body 29 so as to angle the lower part 29b away from the sole plate 22. The lower part 29b of the body 29 is formed with a bore 30 extending from a leading end 30a of the lower part 29b of the body to the trailing end 30b.

A cutting tip 31 of generally bullet-shape has a shank 32 extending from its base, the shank 32 being receivable in the bore 30 of the body 29. The shank 32 is formed with a circumferential groove 33 spaced from the tip 31 such that when the shank 32 is inserted into the bore 30, the tip 31 contacts the leading end, 30a of the body 29 and the groove 33 is positioned adjacent to the trailing end 30b of the body 29. A circlip 34 is engageable with the groove 33 to retain the shank 32 within the body 29.

In the embodiment described, the bore 30 and the shank 32 are of generally circular cross-section so that the cutting tip 31 is free to rotate relative to the body 29. This arrangement allows the cutting tip to rotate during use, so that wear of the cutting tip is distributed round the circumference of the cutting tip 31, to prolong its effective life.

The body 29 is preferably fabricated or cast from high-strength steel. The cutting tip 31 may be formed from hardened steel, or tungsten or other masonry-cutting materials . When attached to the sole plate of the bucket, each of the cutting elements has a maximum extent R_<- from the centre of the bearing bore 25. Preferably, the dimensions R_c are each less than or equal to the distance R_L of the leading edge 27 from the bearing bore 25. This ensures that during pivoting of the bucket through a large angle, the material cleared by the leading edge 27 is sufficient to ensure a clearance for the cutting elements 28. While the side plate has been described as 'arcuate', it is to be understood that the curvature of the side plate need not be constant over its surface, so that for example a sole plate which is past-elliptical in side view is intended to fall within the scope of the invention. The sole plate need only be convexly curved to be effective. The operation of the bucket of the present invention will now be described. In order to form an opening in an asphalt or concrete paved surface, the excavator seen in Figure 1 is fitted with the bucket shown in Figure 2, so that extension and contraction of bucket ram 14 will cause the bucket to pivot about the bearing bore 25 in relation to the arm 6.

The boom 3 and arm 6 are then adjusted so that the cutting element or elements 28 of the bucket which are nearest to the leading edge 27 are placed in contact with the asphalt surface to be penetrated, while the leading edge 27 is kept clear of the surface. Bucket ram 14 is then extended, to pivot the bucket relative to the arm so that the cutting elements 28 are successively drawn across the asphalt surface. Boom ram 5 may be slightly shortened, in order to transfer some of the weight of the vehicle forward to urge the bucket into intimate contact with the asphalt surface.

When the bucket has pivoted through a predetermined angle, so that each of the cutting elements 28 has engaged the asphalt surface, the bucket is lifted slightly away from the surface, and bucket ram 14 is retracted to return the bucket to its original starting position. The bucket is then again urged into contact with the asphalt surface so that the leading cutting elements 28 contact the paved surface. The operation of pressing the bucket into the surface and pivoting the bucket through the small angle required to engage all the cutting elements successively with the paved surface is then repeated. At each pivoting stroke, the cutting elements 28 will break up a shallow surface layer of the paved surface. It may be necessary to use the leading edge 27 of the bucket to clear debris from the cutting area after a number of pivoting cutting strokes. By repeating the pivoting cutting strokes and clearing debris, the paved area will eventually be penetrated.

Figures 5A and 5B are underneath views of the sole plate 22, and show alternative arrangements of the cutting elements 28 on the sole plate.

In the arrangement shown in Figure 5A, three rows of cutting elements 28 extend along the length of the sole plate 22, with the cutting tips 31 of the cutting elements 28 directed towards the leading edge 27 of the sole plate. A central row of cutting elements 28 have their cutting tips 31 aligned perpendicularly to the leading edge 27 of the sole plate, and further rows of cutting elements 28 extending adjacent the side edges of the sole plate have their cutting teeth angled slightly outwardly from the centre line. The cutting teeth 28 are staggered in the fore-and-aft direction of the sole plate, so that as the sole plate is rotated with the cutting elements in contact with a paved surface, so that only one or two of the cutting elements 28 are engaged with the surface at any one time. This enables the force available from the bucket ram to be concentrated on one or two cutting elements 28, rather than distributed over a larger number. The arrangement of cutting elements shown in 5A can be considered as three staggered longitudinal rows of cutting elements 28, or as three helically extending rows of cutting elements.

In the arrangement shown in Figure 5B, a generally symmetrical array of cutting elements 28 is illustrated. A central row of cutting elements is arranged with their cutting tips oriented substantially perpendicularly to the leading edge 27 and the cutting elements on either side of the central row are aligned with their cutting tips 31 angled away from the centre line. The cutting teeth of the central "row" are slightly laterally offset from one another to maximise the cutting effect of each tooth. In the arrangement shown in Figure 5B, the cutting elements 28 engage a paved surface in symmetrical pairs, and this arrangement minimises eccentric loading on the bucket and thus minimises wear in the bucket bearings.

In the arrangement shown in Figures 5A and 5B, the cutting elements are aligned with their cutting tips 31 directed towards the leading edge 27 of the sole plate, so that cutting of the paved surface is effected during an extension stroke of the boom ram 14. While it is foreseen that cutting elements may be arranged on the sole plate with their cutting tips 31 directed away from the leading edge 27, to enable cutting to take place during a contraction stroke of the boom ram 14, such as an arrangement is not preferred. This is because the force available on the contraction stroke of the boom ram is less than that available on its expansion stroke, due to the difference in available cross-sectional area of the boom ram piston. Figure 6 shows an alternative embodiment of the invention, in the form of an excavator tool attachment for fitting to a conventional excavator bucket. In the embodiment shown, the excavator bucket has an arcuate sole plate 22 with a leading edge 27, and the excavator tool attachment comprises an arcuate plate 30 having a hook-like leading section 31 which engages the leading edge 27 of the bucket to secure the leading edge 31 of the tool to the bucket. Adjacent the rear of the bucket, the arcuate plate 30 is secured by means of a chain 32 fixed to a further hook-like portion 33 which engages the top wall of the excavator bucket. A turnbuckle 32a may be provided in the chain 32 for ease of fixing and tightening. Cutting elements 28 are arranged on the convex surface of the arcuate plate 30, in a manner similar to that described in relation to the previous embodiment .

In use, the hook like portion 33 is hooked over the top wall 23 of the excavator bucket, so that the chain extends down the rear wall of the bucket. The arcuate plate 30 is hooked at its end 31 over the leading edge 27 of the bucket, and the rear edge of the arcuate plate is fastened to the chain 32. The chain 32 is then tightened, by means of the turnbuckle 32a. The bucket is then operated as described in relation to the previous embodiment to cut paved areas using the cutting elements 28.

Figures 7 and 8 show a further alternative tool for attachment to a conventional excavator bucket. In the embodiment shown in Figure 7, the tool comprises an arcuate plate 30 having cutting elements 28 as before, and a hooked leading end portion 31 for engagement with the leading edge 27 of the bucket. In this embodiment, a pair of threaded studs 34 extend radially inwardly from the arcuate plate 30. To attach the excavation tool to a bucket, a pair of holes are drilled in the sole plate 22 of the bucket to accept the studs 34. The arcuate plate 30 is then hooked over the leading edge 27 of the sole plate 22, and pivoted about the leading edge 27 to bring the threaded studs 34 through the holes in the sole plate. Nuts 35 are then screwed on to the studs to secure the tool in place on the bucket. As an alternative to the studs 34, aligned holes may be formed in the sole plate 22 and arcuate plate 30 and conventional threaded fasteners may be used to secure the arcuate plate 30 to the sole plate 22.

Figure 9 shows a cutting tooth 48 which is mountable in a body 40, and also shows an alternative method of attaching the body to the sole plate 22 of an excavator bucket. In contrast to the previously described embodiment, the cutting tip 49 is not rotationally symmetrical about the cutting tooth axis 50. In this example, the cutting tooth 48 has a chisel edge, similar to cutting tools used in mining or tunnelling applications. In use, the cutting tooth 48 is preferably arranged to engage the asphalt or concrete surface that is to be penetrated with the chisel edge 49 oriented generally horizontally, i.e. generally parallel to the sole plate 22 of the excavator bucket. In order to maintain the correct orientation of the cutting tip 49, the cutting tooth 48 has a square shank 47 which is receivable in a correspondingly shaped square bore 51 in the body 40. A circlip 44 is engageable with a circular portion 45 at the end of the shank 47 remote from the tooth 48, to retain the square shank 47 within the body 40. Although the shank 47 and bore 51 are square in cross-section in the illustrated embodiment, it will be understood that any non-circular section of the shank and bore will serve to prevent rotation of the shank relative to the body 40. Figure 9 also illustrates an alternative method of attaching the body 40 to the sole plate 22, in contrast to those described earlier. In this example, two studs 41 extend from the end of the body remote from the cutting tooth 48 and pass through corresponding holes (not shown) in the sole plate 22. The body is secured to the sole plate by placing washers 42 on the studs 41 and tightening nuts 43 on the washers. This method of attachment of the body 40 has the advantage that it may allow cutting teeth to be attached easily to conventional excavator buckets 9 without the need for welding.

Figure 10 shows an alternative embodiment of the invention in which a body 60 of generally rectangular cross-section is attached to the sole plate 22 of an excavator bucket. A pair of threaded studs 61 extend laterally from the body 60 at a spacing from the bucket 22.

A cutting tooth 62 comprises a generally rectangular central portion and two cutting edges 63 and 64 at its respective ends . The central portion is further formed with bores 65 to receive the studs 61, and counterbores 66 to receive nuts 67 engageable with the studs 61 to retain the cutting tooth to the body 60. The body is preferably aligned relative to the bucket so that the cutting edges 63 and 64 are in a plane perpendicular to the pivoting axis 10 of the bucket.

The central portion of the cutting tooth 62 is recessed at 70 to receive the body 60, so that loads from the cutting edges 63 and 64 can be transmitted to the body by abutment surfaces 72 and 74, and abutment surfaces 71 and 73, respectively. This arrangement minimises transverse load on the studs 61. The bores 65 and counterbores 66 may be elongated in the cutting direction to provide clearance. The cutting tooth 65 is able to cut on both a forward stroke, corresponding to an extension of the bucket ram 14, and a return stroke corresponding to a retraction of the bucket ram 14. This reduces the need to lift the bucket between cutting strokes as the return stroke is now also a cutting stroke. The bidirectional reciprocable cutting tooth 62 may have a forward cutting edge 63 which is of a different size and shape from the reverse cutting edge 64. This is because the bucket ram 14 is able to exert a greater force during extension than during retraction, due to the different effective piston areas available on the two strokes .

Figure 11 shows an alternative embodiment of the invention in the form of an excavator tool for penetrating paving. The excavator tool comprises a generally arcuate sole plate 70, to the concave face of which a central upstanding web 71 is attached. A pair of bearing bores 72 and 73 extend transversely across the upper edge of the web 71, with the axis of bearing bore 72 substantially coincident with the axis of the arcuate sole plate 70. Reinforcing fillets 74 and 75 extend from the bearing tubes 72 and 73 respectively to the sole plate 70, and are attached to the web 71.

The convex face of the sole plate 70 is formed with a number of cutting teeth 76 as described in relation to Figure 3, arranged to project substantially tangentially relative to the sole plate 70, toward its leading edge

70a.

In the tool shown in Figure 11, a pair of edging blades 76 are placed adjacent the leading edge 70a of the sole plate, to extend substantially perpendicularly to the sole plate at its lateral edges . The function of these blades is to initially cut the concrete or asphalt to produce a smooth edge to the trench by preventing chipping of the concrete beyond the trench width by the cutting teeth 75.

In use, the bearing bores 72 and 73 accept pivot pins (not shown) to attach the tool to the arm 6 and bucket ram 14 of an excavator, respectively. The tool is operated by urging it into contact with the paved surface, and extending the boom ram 14 to draw the edging blades 76 and cutting teeth 75 across the paving, as described above in relation to the bucket embodiments.

The edging blades 76 initially form two slits to delineate the edges of the trench, and the paved area between the slits is then broken up by the cutting teeth 75.

Claims

Claims :

1. An excavator tool pivotally mountable to an arm of an excavator, the excavator tool comprising: mounting means for pivotally mounting the tool to the arm for pivoting movement about a pivot axis; means for rotating the tool relative to the arm about the pivot axis ; a convex surface arranged substantially concentrically with the pivot axis; a number of cutting elements arranged on the convex surface, the cutting elements having respective cutting tips arranged to project radially from the convex surface .

2. An excavator tool according to claim 1, wherein the convex surface is substantially arcuate in form.

3. An excavator tool according to claim 1 or claim 2, wherein the means for rotating the tool relative to the arm comprises means for pivotally connecting the tool to an actuator mounted on the arm of the excavator.

4. An excavator tool according to any preceding claim, wherein each of the cutting elements comprises a body having a first portion extending substantially radially from the convex surface, and a second portion extending substantially tangentially relative to the convex surface, the cutting tip of each cutting element being arranged at a free end of the said second portion.

5. An excavator tool according to any preceding claim wherein the cutting elements are arranged with their cutting tips directed towards a leading end of the convex surface .

6. An excavator tool according to any of claims 1 to 5 , wherein a plurality of cutting elements are arranged on the convex surface and wherein some of the cutting elements are arranged with their cutting tips directed towards a leading end of the convex surface, and others are arranged with their cutting tips directed away from the leading end of the convex surface.

7. An excavator tool according to any preceding claim, wherein a cutting blade extends substantially radially relative to the sole plate at a lateral edge of the convex surface adjacent a circumferential end thereof.

8. An excavator tool according to claim 7 wherein each lateral edge of the convex surface is provided with a respective cutting blade extending radially therefrom.

9. An excavator tool according to any preceding claim wherein the cutting elements are arranged on the convex surface in staggered relationship with respect to the circumferential direction of the convex surface.

10. An excavator tool according to any preceding claim wherein the mounting means comprises one or more co-axial first bearing bores.

11. An excavator tool according to any preceding claim wherein the means for rotating the tool relative to the arm comprises at least one second bearing bore spaced from, and having its axis parallel to, the pivot axis.

12. A bucket for a mechanical excavator having a movable arm, the bucket comprising: mounting means for mounting the bucket to the arm for rotation relative to the arm about a pivot axis extending transversely to the length of the arm; means for rotating the bucket relative to the arm; a pair of side walls extending substantially perpendicularly to the pivot axis ; a rear wall extending between the side walls and substantially radially of the pivot axis; a sole plate extending from the rear wall and joined to the rear wall and to the side walls at their respective edges remote from the pivot axis; a transverse leading edge of the sole plate extending between the side walls; and wherein at least a part of the sole plate is generally arcuate in form and is arranged substantially coaxially with the pivot axis of the mounting means, and wherein a number of cutting elements are arranged on the convex surface of the arcuate part of the sole plate, the cutting elements facing generally in the direction of the leading edge of the sole plate.

13. A bucket according to claim 12 wherein the mounting means for mounting the bucket to the arm comprises one or more coaxial first bearing bores in which a bearing pin is receivable.

14. A bucket according to claim 12 or claim 13 wherein the means for rotating the bucket relative to the arm comprises attachment means provided on the bucket at a position radially spaced from the pivot axis of the mounting means , the attachment means adapted for attachment to an actuator mounted to the arm of the excavator.

15. A bucket according to any of claims 12 to 14 wherein the means for rotating the bucket relative to the arm comprises one or more coaxial second bearing bores spaced from the first bearing bores and paraxial therewith, for engagement with an actuator mounted to the arm.

16. A bucket according to any of claims 12 to 15, wherein each of the cutting elements comprises a body having a first portion extending substantially radially from the arcuate part of the sole plate, and a second portion extending substantially tangentially relative to the arcuate part of the sole plate, the cutting tip of each cutting element being arranged at a free end of the said second portion.

17. A bucket according to any of claims 12 to 16, wherein the cutting tips of the cutting elements are directed towards the leading end of the sole plate.

18. A bucket according to claim 17 wherein the cutting tips of the cutting elements are angled obliquely towards the leading edge of the sole plate.

19. A bucket according to any of claims 12 to 18 wherein the cutting elements are arranged in staggered rows extending substantially perpendicularly to the leading edge of the sole plate.

20. A bucket according to any of claims 12 to 16, wherein a plurality of cutting elements are arranged on the sole plate and wherein some of the cutting elements have their cutting tips directed towards the leading edge of the sole plate, and others of the cutting elements are arranged with their cutting tips directed away from the leading end of the sole plate.

21. A bucket according to any of claims 12 to 20, wherein at least one cutting element has two cutting tips facing opposite directions.

22. A bucket according to any of claims 12 to 21, further comprising a cutting blade extending substantially radially of the sole plate at a lateral edge of the sole plate adjacent the leading edge.

23. A bucket according to claim 22, comprising a pair of cutting blades extending substantially radially of the sole plate from respective lateral edges of the sole plate adjacent the leading edge.

24. A bucket according to any of claims 12 to 23, wherein the radial distance from the pivot axis to the transverse leading edge of the sole plate is equal to or greater than the radial distance from the pivot axis to the cutting elements .

25. An excavator attachment for an excavator bucket mountable to an excavator arm for pivoting movement relative to the arm about a pivot axis , the attachment comprising: a generally arcuate sole plate mountable to the excavator bucket so as to be substantially co-axial with the pivot axis ; means for attaching the sole plate to the excavator bucket; and a number of cutting elements arranged on the convex surface of the sole plate, the cutting elements having respective cutting tips arranged to project radially from the convex surface of the sole plate.

26. An excavator attachment according to claim 25 for use with an excavator bucket having a sole plate with a transverse leading edge, wherein the means for attaching the excavator attachment to the bucket comprises a hook portion to engage the leading edge of the sole plate of the bucket .

27. An excavator attachment according to claim 25 or claim 25, wherein the attachment means comprises a threaded fastener.

28. An excavator attachment according to claim 25 or claim 25, wherein the attachment means comprises a threaded clamp.

29. An excavator comprising: a movable arm; an excavation tool pivotally mounted to an end of the movable arm for pivoting movement relative to the arm about a pivot axis ; actuator means for reciprocally rotating the tool relative to the arm about the pivot axis; wherein the excavation tool comprises a convex surface arranged substantially concentrically with the pivot axis and a number of cutting elements arranged on the convex surface, the cutting elements having respective cutting tips arranged to project radially from the convex surface.

30. An excavator according to claim 29, wherein the convex surface of the excavation tool is part of an arcuate sole plate.

31. An excavator according to claim 29 or claim 30, wherein the excavation tool further comprises a cutting blade extending substantially radially from the convex surface at a lateral edge thereof.

32. An excavator according to any of claims 29 to 31, wherein the cutting elements are arranged on the convex surface in staggered relationship with respect to the circumferential direction of the convex surface.

33. A method of forming an opening in a paved area using an excavator tool according to any of claims 1 to 11, an excavator bucket according to any of claims 12 to 24, an excavator attachment according to any of claims 25 to 28 or an excavator according to any of claims 29 to 32, mounted to a movable arm of an excavator, the method comprising the steps of: moving the arm of the excavator so as to urge the cutting elements of the excavator tool into contact with the paved area; and rotating the excavator tool relative to the arm to move the cutting elements into the paved surface.

34. A method according to claim 33 wherein the arm is continually urged towards the paved area while the tool is rotated in a first sense in cutting arrangement with the surface, and moving the arm to space the tool from the surface during rotation of the tool relative to the arm in a second sense opposite to the first.

35. An excavator tool substantially as herein described with reference to Figures 1 to 5, or Figure 11 of the accompanying drawings.

36. An excavator bucket substantially as herein described with reference to Figures 1 and 2 of the accompanying drawings .

37. An excavator attachment substantially as herein described with reference to Figures 6, 7, or 8 of the accompanying drawings .

38. A method of penetrating a paved surface, substantially as described herein.