It is known to install anchor bolts which are used to reinforce a structure, such as a bridge, by way of a tie between the fixed anchor bolt and the structure. Anchor bolts are also used in the fields of tunnelling and mining, and are used to secure masonry facings on buildings, and as high quality cavity wall tie replacement in brick and stonework.

In order to fix an anchor bolt a hole must be formed in which the bolt can be placed together with a filler such as grout. Various methods are known for producing such holes however all suffer from various disadvantages including lack of anchorage strength provided by the hole and the formation of a hole whose shape is not readily controllable.

The present invention seeks to provide an improved drill assembly.

According to one aspect of the invention there is provided a drill assembly comprising cutter means and guide means, the guide means comprising a longitudinal axis, the cutter means being mounted for pivotal movement which is generally lateral of the longitudinal axis of the guide means about respective pivot axes which are substantially parallel to the longitudinal axis of the guide means, the arrangement of the assembly being such that, in use, the cutter means engages with the guide means, and the cutter means being caused to rotate about the longitudinal axis of the guide means and have a component of movement in a direction which is generally parallel to said longitudinal axis, and the

guide means being shaped so as to move the cutter means generally laterally of the longitudinal axis.

Advantageously the guide means can be formed to a desired shape and in use the guide means will advantageously enable a hole of that shape to be accurately formed. In a preferred embodiment of the invention the guide means is shaped so as to cause the cutter means to produce a hole of variable diameter, and in particular, a flared hole.

Preferably the guide means comprises a generally elongate member which is adapted to be positioned in a pre-formed hole.

Preferably the guide means comprises a guide surface and in use the cutter means engages with the guide surface so as to determine the lateral movement of the cutter means.

The guide means preferably comprises a first substantially frusto-conical portion.

The guide means may comprise a second substantially frusto-conical portion, the direction in which the second frusto-conical portion tapers being opposite to that in which the first frusto-conical portion tapers.

It will be appreciated however that the guide means may comprise a plurality of substantially frusto-conical portions which taper in a common direction. <BR> <BR> <BR> <BR> <BR> <BR> <P>The second substantially frusto-conical portion is desirably provided towards a distal end of the guide means.

Preferably the cutter means is resiliently biased against the guide means.

The cutter means may comprise a plurality of pivotally mounted cutters.

Advantageously, a plurality of pivotally mounted cutters arranged around the guide member provides a high degree of cutter surface coverage.

Preferably a cutting surface of the cutter means is substantially arcuate.

According to a second aspect of an invention there is provided a method of forming a hole comprising the steps of: inserting guide means into a pre-formed hole, the guide means comprising a longitudinal axis and comprising a variable diameter portion; arranging that cutter means engages with the guide means; causing the cutter means to rotate about the longitudinal axis of the guide means and to have a component of movement in a direction which is substantially parallel to said longitudinal axis, and causing the cutter means to move generally laterally of the longitudinal axis about pivot axes which are substantially parallel to the longitudinal axis.

According to a third aspect of the invention there is provided a drill cutter assembly comprising cutter means for engaging with guide means, the cutter means being adapted to rotate about a longitudinal axis of the guide means, and being adapted to move generally laterally of the longitudinal axis about pivot axes which are substantially parallel to the longitudinal axis as a result of engagement with an outer surface of said guide means.

Various embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which : - Figure 1 is a plan view of a cutter arrangement of a drill assembly in accordance with the invention in which one cutter limb is shown in fully extended position, Figure 2 is an exploded view of a housing and a guide member of the cutter arrangement as shown in Figure 1, Figure 3 is a partial exploded plan view of the cutter arrangement shown in Figure 1, Figure 4 is a side elevation of the view shown in Figure 3, Figure 5 is a perspective view of a guide member of a second embodiment of a drill assembly in accordance with the invention, Figure 6 is a part-exploded perspective view of a housing of the second embodiment, Figures 7a-7f are perspective views of progressive'snap-shots'of the second embodiment in use, Figure 8 is an enlarged perspective view of the second embodiment in use, Figure 9 is an-exploded perspective view of a third embodiment of the drill assembly in accordance with the invention, Figures lOa-lOf are perspective views of progressive'snap-shots' of the third embodiment in use, and

Figure 11 is an enlarged perspective view of the third embodiment in use.

Figures 1,2, 3 and 4 show a drill assembly comprising guide means and a drill bit assembly comprising cutter means. The guide means comprises a guide member 2 of generally elongate construction having a longitudinal axis A-A and comprising an upper portion 5 and a lower portion 6.

The upper portion 5 is of substantially cylindrical shape, and the lower portion 6 is of substantially frusto-conical shape. The lower portion 6 has a cone angle a given by tan-' (1/100) (which it has been found provides a high quality anchorage).

That distal end of the guide member 2 which is adjacent to the upper portion 5 is provided with a substantially circular washer 109 and that distal end of the guide member 2 which is adjacent to the lower portion 6 is provided with a substantially circular washer 11.

The cutter means comprises cutter arrangement 50 comprising five equally angularly spaced cutter limbs 51 which are mounted for pivotal movement. The arrangement 50 is located at a distal end portion 55 of a housing 9 of generally cylindrical tubular form. The opposite distal end 14 of the housing is adapted to interface with drive means (not shown). It is envisaged that the outer diameter of the housing 9 will be between approximately 300mm and 75mm.

Each cutter limb 51 comprises an arcuate cutter face which comprises two arcuate cutter portions 57a and 57b made of suitably hardened material, such as diamond dust in a metal matrix. Each limb 51 further comprises an abutment portion 56, a guide engagement portion 58, a first

curved portion 60, a second curved portion 61 and a third curved portion 62.

With reference in particular with Figures 3 and 4 the limbs 51 are sandwiched between a lower plate 53 and an upper plate 64. The lower plate 53 is of generally annular shape and is provided with five equally angularly spaced holes 65 and a central aperture 66. The upper plate 64, which is fixed to the lowermost portion 55, is also of generally annular shape and is provided with five equally angularly spaced holes 67 and a central aperture 68.

In an assembled state five capscrews comprising a head 69 and a pin 71 are passed through aligned holes 65 and 67 and through pivot holes 70 of each of the limbs 51.

A spring 72 is located by each of the capscrews, the spring 72 comprising two arms 74 and 75. The arm 74 is arranged to bear against an inner surface 76 of the lower plate 53 and the arm 75 is arranged to bear against the third curved portion 62 of each respective limb 51.

The cutter arrangement 50 operates as follows. The guide member 2 is lowered into a pre-formed hole of substantially constant diameter until the washer 11 sits on the base of the pre-formed hole. As the arrangement 50 is caused to rotate about the longitudinal axis of the guide member, the guide (by virtue of the housing 9 being rotated about axis A-A by the drive means) engagement portions 58 of the cutter limbs 51 engage with the guide member. As the cutter arrangement is caused to move progressively downwards into the pre-formed hole the lower portion 6 of the guide member causes the limbs to pivot generally laterally of the longitudinal axis about an axis which is defined by each of the capscrews 69 so as to form a reamed hole 78. As the limbs 51

move progressively laterally outwards, different portions of the cutter portions 57a and 57b come into contact with the material (of the pre- formed hole) which is drilled.

A substantially frusto-conical recess is thus formed.

The cutter surfaces 35b', 35c'and 35d'of each cutter block gradually wear away through use and in so doing expose fresh cutting surfaces until eventually no cutting material remains and the cutter blocks need to be replaced.

With reference to Figures 5,6, 7 and 8 there is shown a second embodiment of the invention which comprises a substantially cylindrical housing 80 and a guide member 81.

The guide member 81 comprises an upper portion 83 of generally cylindrical form and a lower portion 84 of generally frusto-conical form.

The upper portion 83 is provided with two so-called spiders 85 which are of a tri-limbed configuration. One spider 85 is located at an uppermost distal end of the upper portion 83 and is held in position by way of two nuts 86 on each side of the spider 85. The other spider 85 is located towards a lowermost end of the upper portion 83 and is similarly held in position by two flanking nuts 86.

The lower portion 85 is provided at a lowermost distal end thereof with shaft 87 which is of substantially cylindrical form. Attached to a lowermost distal end of the shaft 87 by way of a nut 88 is a washer 89.

The housing 80 is of tubular form and comprises at a lowermost distal end thereof a cutter arrangement. The cutter arrangement comprises

three cutter limbs 90, each of which comprises a suitably hardened material portions 91 which provide cutter faces of arcuate outline.

The cutter limbs 90 are pivotally mounted (through holes 90a of each cutter limb 90) on respective pins 92, which pins extend outwardly of the housing 80 and around a central aperture 93.

The aperture 93 is defined by inner surface portions 94 so that said aperture is of substantially the same outline as that of each of the spiders 85.

A plate 95 and nuts 96 act to secure the cutter limbs in position on the housing 80. The plate 95 is provided with through-holes 97 which receive respective pins 92 so that the portion of each pin which protrudes through holes 97 is available for the respective nuts 96 to be attached thereto.

The plate 95 comprises three outwardly extending formations 98 which are circumferentially interposed between through holes 97. The purpose of such formations is to allow sacrificial wear of those formations before wear of the nuts 96 takes place.

It is envisaged that the outer diameter of the housing 80 will be between approximately 100mm and 20mm.

In use the drill assembly operates as follows. The guide member 81 is first positioned inside the housing 80 so that engagement surfaces 99 of each cutter limb contact with upper portion 83, and thus the cutter limbs are in a fully retracted condition (as shown in Figure 7a). Abutment portions 100 of the spiders 85 contact with an inner surface of the housing 80 so that the longitudinal axis B-B of the guide member 80

remains coincident with the longitudinal axis (not referenced) of the housing and in order that a frictional engagement therebetween ensures that the housing and the guide member remain sufficiently axially spaced when the assembly is lowered into a pre-formed hole (as discussed below). However, the abutment portions 100 have frictional characteristics such that relative sliding movement between the abutment portions and the inner surface of the housing 80 is possible during drilling.

The assembly is lowered into a pre-formed hole 101 until the washer 89 sits on the base thereof. In such a condition the cutter faces are proximal to the mouth of the pre-formed hole. The housing 80 is then both rotated about the axis B-B of the guide member 81 and urged generally downwardly. As is evident from Figures 7b, 7c, 7d and 7e, as the engagement portions 99 of each cutter limb 90 contact with the lower portion 84 of the guide member 81 the limbs are moved progressively outwards and in so doing form a hole 102 of substantially frusto-conical shape. Reference is made in particular to the enlarged view shown in Figure 8.

As continued downward movement of the housing 80 is produced the engagement portions 99 of the cutter limbs 90 eventually pass over the lowermost end of the lower portion 84 and onto the shaft 87 and in so doing the cutter limbs adopt a fully retracted condition so that the assembly can be readily removed from the hole.

A third embodiment of the invention is shown in Figures 9,10 and 11.

The drill assembly shown therein comprises a housing 110 and a guide member 111.

The housing 110 is of generally cylindrical tube form and comprises at a lowermost distal end thereof two cutter components 120. Each cutter component 120 comprises a shaft 121 which at one distal end thereof there is provided a locating head 122 and at the opposite distal end thereof there is provided a cam follower 123. The cam follower 123 comprises an end surface portion 124 which is adapted to receive a part annular portion 125 which is formed of hardened material so as to form a cutter surface.

The cam follower 123 further comprises a nib 126 which is flanked by recesses 127 and 128 (as best seen in Figure 11).

Each locating head 122 is received by a respective through hole 129 and a shank portion (unreferenced) which interposes the locating head and the shaft 121 and is accommodated in a semicircular recess 130 which is provided adjacent to each through hole 129.

The housing 110 is further provided with two diametric longitudinal slots 131 which are open at the lowermost distal end of the housing 110 and are adapted to receive the respective shafts 121.

It is envisaged that the outer diameter of the housing 110 is between approximately 32mm and 12mm.

Turning now to the guide member 111 which comprises four elongate channels 112 and 113 (only two of which are shown in Figure 9, but the remaining channels comprise two channels identical to each of channels 112 and 113). The four channels are circumferentially spaced around the longitudinal axis C-C of the guide member.

The channels 113 are of general arcuate cross-sectional outline and are adapted to receive the shaft of each respective cutter component 120.

The channels 112 are essentially of v-shape and each comprise three defining surfaces 112a, 112b and 12c and are adapted to receive the nib 126 of the cam follower 123.

At the uppermost end of the guide member 111, when viewed in transverse cross-section, the surfaces 112b and 112c form two inclined side walls and the surface 112a forming a'basal'surface. As the surface 112a extends along the guide member 111 in a downwardly direction towards the basal portion 137, said surface may generally be described as a flat'rising'ramp. In other words with progressive downward axial position the surface 112a correspondingly extends progressively outwards of the axis C-C. Moreover, the surface 112a 'twists'outwardly of the guide member 111 with progressive downward position, i. e. the direction normal to each axially-spaced portion of the surface 112a rotates with downward position along the guide member 111.

As will be appreciated the radial height of the surface 112c reduces with downward axial position.

The surface 112b is essentially of curved configuration (as best seen in Figure 9) so as to allow for sufficient clearance of the nib 126 with progressive downward movement.

Longitudinally spaced from each channel 112 by an intermediate surface 135 there is provided a recess 136.

The lowermost end of the guide member 111 comprises a basal portion 137 which is of substantially frusto-conical shape and is provided with a'tip'138.

The housing 110 is provided with a pair of diametric holes 132 which serve to locate means situated inside the housing for maintaining, by way of frictional engagement between said means and the guide member, that when the guide member and the housing are lowered into a pre-formed hole (as seen in Figure 10a), the guide member and the housing remain axially spaced until the guide member reaches the base of the hole, thus preventing the guide member from falling under its own weight.

In use the drill assembly operates as follows. The housing 110 and the guide member 111 are lowered into a pre-formed hole 140, as us seen in Figures 10a and lOb. The housing 110 and the guide member 111 are both rotated about axis C-C and, simultaneously, the housing is urged generally downwards.

As the housing 110 progressively moves downwards the shafts 121 move along the channels 113 and engagement between the surfaces 112a and the nibs 126 causes the pivoting of the cutters which movement is generally lateral of the axis C-C.

When the cam followers 123 reach the end of the channels 112 the channels 112 become contiguous with the respective intermediate surfaces 135, and further downward movement urges the nibs 126 over the intermediate surfaces 135 and into the recesses 136, the part annular cutter portions 125 thus adopting a fully retracted condition.

As is evident from Figures 10c, 10d, 10e and 10f a frusto-conical hole 141 is thus formed.

It is to be noted that, unlike the embodiment shown in Figures 1 to 4, the embodiments of Figures 5 to 8, and Figures 9 to 11, respectively, do not require a spring or other resilient means which acts to bias the cutters inwardly of the longitudinal axis of the respective guide member. This is because in both of those latter embodiments, as the respective housing is rotated about the longitudinal axis of the guide member, the portion of hardened cutter material has a moment about its respective pivotal axis and the rotation of the housing acts to give each cutter some leverage against the guide member. The fact that a spring or other resilient member does not need to be incorporated into the cutter arrangement advantageously allows the overall dimensions of an assembly to be drastically reduced. It will be appreciated however that the embodiment shown in Figures 1 to 4 that the cutter limbs 51 do also possess, to a certain extent, such an inwardly directed leverage in addition to the force applied to each by the respective springs.

Although the guide member of the embodiments hereinbefore described comprises a substantially frusto-conical portion, a guide member in accordance with the present invention may comprise a portion which curves outwardly to produce what may be termed as a'bell-shape'so as, in use, to cause lateral movement of the cutter means.

It will be appreciated that a guide member may comprise a plurality of adjacent frusto-conical portions tapering in the same direction.