Related Applications

[0001] This application is related to Australian Provisional Patent Application

No. 2019901454, filed on 30 April 2019, the entire content of which is hereby incorporated by reference.

Technical Field

[0002] The present disclosure relates to tunnelling and mining machines that have a rotating cutter drum. In particular, the present invention relates to apparatus and methods of mounting fixed orientation cutting tools and tool holders to the cutter drum.

Background of the Invention

[0003] Tunnelling, road excavation and mining machines, such as roadheaders, road planing machines, continuous miners, longwall shearers and other excavation machines, typically employ a rotating cutter drum to which an array of cutting tools is fixed. As the rotating cutter drum is pressed into the surface, the cutting tools tear or cut into the surface dislodging rock or ore which is then collected and conveyed away from the cutting face. During use, the cutting tools, which are commonly tungsten carbide tipped or diamond tipped, wear away and become blunt and need to be replaced.

[0004] The cutting tools are typically mounted in tool holders, which are in turn welded to spiralling vanes on the cutter drum. The cutting tools are usually releasably secured in the tool holders so that the cutting tools can be replaced as they wear and become blunt. Fixed orientation cutting tools have a forward facing blade or tip and need to be secured in a fixed orientation with the blade or tip facing in the general direction of travel.

[0005] As the cutter drum is pressed into the surface, the cutting tools and the tool holders are subjected to high loads of shear stress, bending moments, compression stress, vibrations, etc. Furthermore, as the cutting tools become worn and blunt, the forces placed on the cutting tools and the tool holders increase significantly and commonly cause damage to the cutting tools and tool holders. Damaged tool holders often fail to retain the cutting tools during operation and the cutting tools can become dislodged. Empty tool holders are further damaged during operation of the cutter drum and, in underground mining operations, can result in frictional ignition of flammable gases in the mine, causing an explosion and leading to damaged equipment, the collapse or shutdown of the mine and potential loss of life.

[0006] To minimise dust, suppress ignition potential, and to cool the fixed orientation cutting tools, spray nozzles are typically located behind (or alternatively, in front of) each cutting tool in order to spray water over the cutting tool and the mine face during operation. When the tool holders become damaged, or when the cutting tools themselves shear, the spray nozzles are often damaged and become inoperable.

[0007] Further, in underground mining operations, it is often not permissible and/or dangerous to use welding or grinding equipment to repair damaged tool holders due to flammable gases in the mine. This means that when tool holders become damaged, the entire cutter drum needs to be removed and returned to the surface, where it can be repaired. This process requires the mining operation to cease while the cutter drum is removed and repaired, or at least while the cutter drum is removed and replaced with a substitute cutter drum.

[0008] For certain applications or for better performance, the fixed orientation cutting tools are often required to be secured to the vanes of the cutter drum in different positions and/or orientations, with the cutting tools differing in angle of attack and/or yaw and/or depth. This requires complicated and difficult welding operations to ensure that each tool holder is welded to the cutter drum in the correct position and orientation and with sufficient pre-heat temperature. Consequently, the welding operation is time consuming and requires a high level of technical expertise, resulting in a very expensive manufacturing process.

Object of the Invention

[0009] It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages, or to provide a useful alternative.

Summary of the Invention

[0010] In a first aspect, the present invention provides a tool holder assembly comprising: a mounting block having a front end, a rear end, and a first cavity extending into the mounting block from an upper surface; and

a fixed orientation cutting tool having a cutting head and a mounting portion, wherein the mounting portion is shaped to fit into the first cavity;

wherein the first cavity has a cross-sectional shape that tapers inwardly from opposing end portions such that an intermediate portion is narrower in cross-sectional profile than the end portions.

[0011] In a preferred embodiment, the mounting portion of the cutting tool has a cross- sectional shape that tapers inwardly from opposing end portions such that an intermediate portion is narrower in cross-sectional profile than the end portions.

[0012] Preferably, the mounting portion of the cutting tool is releasably securable to the mounting block.

[0013] Further preferably, the first cavity extends at an obtuse angle to an upper surface at the front end of the mounting block and the mounting portion of the cutting tool projects at a corresponding angle to a base of the cutting head.

[0014] In a preferred embodiment, the tool holder assembly further comprises a tool support member including a projection that has a second cavity, wherein the projection is shaped to fit into the first cavity in the mounting block and the mounting portion of the cutting tool is shaped to fit into the second cavity in the tool support member, such that the tool support member is an intermediary between the mounting block and the cutting tool.

[0015] Preferably, the second cavity has a cross-sectional shape that tapers inwardly from opposing end portions such that an intermediate portion is narrower in cross-sectional profile than the end portions.

[0016] Preferably, the projection has a cross-sectional shape that tapers inwardly from opposing end portions such that an intermediate portion is narrower in cross-sectional profile than the end portions.

[0017] In a second aspect, the present invention provides a tool for a tool holder assembly, the tool comprising:

a cutting head; and

a mounting portion having a cross-sectional profile that tapers inwardly from opposing end portions such that an intermediate portion is narrower in cross-sectional profile than the end portions.

[0018] In a preferred embodiment, the cross-sectional profile generally resembles a bow tie shape with wider end portions and a narrower intermediate portion.

[0019] Preferably, the mounting portion of the cutting tool projects at a swept back obtuse angle to a base of the cutting head.

[0020] In a third aspect, the present invention provides a tool holder assembly comprising: a mounting block having a front end, a rear end, and a first cavity extending into the mounting block from an upper surface;

a tool support member including a projection, wherein the projection has a second cavity and the projection is shaped to fit into the first cavity; and

a fixed orientation cutting tool having a cutting head and a mounting portion, wherein the mounting portion is shaped to fit into the second cavity.

[0021] In a preferred embodiment, the projection of the tool support member fits snugly within the first cavity and the mounting portion of the cutting tool fits snugly within the second cavity.

[0022] Preferably, the tool support member is releasably securable to the mounting block. Further preferably, the mounting portion of the cutting tool is releasably securable to the tool support member.

[0023] In a preferred embodiment, the first cavity has a first cross-sectional shape and the projection of the tool support member has a complementary external cross-sectional profile.

[0024] Preferably, the first cross-sectional shape tapers inwardly from opposing end portions such that an intermediate portion is narrower in cross-sectional profile than the end portions.

[0025] Further preferably, the second cavity has a second cross-sectional shape and the mounting portion of the cutting tool has a complementary external cross-sectional profile.

[0026] Preferably, the second cross-sectional shape tapers inwardly from opposing end portions such that an intermediate portion is narrower in cross-sectional profile than the end portions. [0027] In a preferred embodiment, the first cavity extends at an obtuse angle to the upper surface at the front end of the mounting block and the projection projects at a

corresponding obtuse angle to the upper portion of the tool support member.

[0028] Preferably, the second cavity extends at the same angle as the projection.

[0029] In a preferred embodiment, the tool holder assembly further includes a removable spray device, wherein the spray device has a spray head and a base portion extending from the spray head.

[0030] Preferably, the tool holder assembly further includes a removable support component having a first aperture, wherein the support component is shaped to fit in a recess in the mounting block and wherein the base portion of the spray device is shaped to fit within the first aperture of the support component.

[0031] Further preferably, the spray device is replaceable independently of the tool support member and the cutting tool.

Brief Description of the Drawings

[0032] A preferred embodiment of the invention will now be described by way of specific example with reference to the accompanying drawings, in which:

[0033] Fig. 1 depicts a first embodiment of a tool holder assembly in an assembled configuration;

[0034] Fig. 2 is an exploded view of the tool holder assembly of Fig. 1;

[0035] Fig. 3 is a side elevation exploded view of the tool holder assembly of Fig. 1;

[0036] Fig. 4 is a top view of a mounting block in isolation;

[0037] Fig. 5 is a top view of a tool support member in isolation;

[0038] Fig. 6 depicts a spray mounting component in isolation;

[0039] Fig. 7 is a top view of a spray device;

[0040] Fig. 8 is a side elevation view of the spray device of Fig. 7;

[0041] Fig. 9 is an exploded view of a second embodiment of a tool holder assembly;

[0042] Fig. 10 is a top view of a mounting block of the second embodiment in isolation;

[0043] Fig. 11 is a top view of a tool support member of the second embodiment in isolation; [0044] Fig. 12 is a side elevation view of the tool support member of Fig. 11;

[0045] Fig. 13 is a cross-sectional view of the projection of the tool support member of Fig. 12;

[0046] Fig. 14 is a side elevation view of a cutting tool of the second embodiment in isolation;

[0047] Fig. 15 is a cross-sectional view of the mounting portion of the cutting tool of Fig. 14; and

[0048] Fig. 16 is an exploded view of a third embodiment of a tool holder assembly.

Detailed Description of the Preferred Embodiments

[0049] Fig. 1 depicts a first embodiment of a tool holder assembly 100 in assembled form. Fig. 2 and Fig. 3 depict the same tool holder assembly 100 in an exploded view. The tool holder assembly 100 includes a mounting block 110, a tool support member 130 (or tool sleeve), a fixed orientation cutting tool 150, a spray device 170, and a spray mounting component 180.

[0050] The mounting block 110 has a front end 112, a rear end 114, an upper surface 116, a first cavity 118, and a spray device recess 120. The first cavity 118 extends downwardly into the mounting block 110 from an opening in the upper surface 116 and may be closed or extend entirely through the mounting block 110 to an opening at the base of the mounting block 110. In the embodiment depicted, the first cavity 118 has a constant cross-sectional profile being in the shape of a rounded isosceles trapezium (best shown in Fig. 4).

Transverse apertures 122 are provided laterally through the mounting block 110, passing transversely into and through the first cavity 118.

[0051] The spray device recess 120 is located at the rear end 114 of the mounting block 110 and is a generally rounded rectangular cut out extending into the mounting block 110 from an opening in the upper surface 116 and is also open from the rear end 114. A fluid delivery passage 124 extends through the mounting block 110 from the base of the spray device recess 120.

[0052] The tool support member 130 has an upper portion 132 and a projection 134 that extends downwardly from the upper portion 132. A second cavity 136 extends downwardly within the projection 134 from an opening in the upper portion 132 and may be closed or extend entirely through the projection 134 to an opening at the base of the projection 134. A spray device aperture 138 through the upper portion 132 is provided rearward of the second cavity 136 for receiving the spray device 170.

[0053] The projection 134 of the tool support member 130 is shaped to fit into the first cavity 118. In the embodiment depicted, the projection 134 has an external shape that is substantially complementary to that of the first cavity 118 with length and width dimensions slightly smaller than the first cavity 118 and with chamfered corners 140. These dimensions are such that the projection 134 fits snugly within the first cavity 118 with only minimal, if any, frictional interference between the components allowing the projection to slide into and out of the first cavity 118. In an alternative embodiment, the projection 134 may be secured by interference fit within the first cavity 118.

[0054] In the embodiment depicted, the second cavity 136 has a tapering opening leading into a lower portion with a constant cross-sectional profile being in the shape of a rounded rectangle (best shown in Fig. 5). Transverse apertures 142 are provided laterally through the projection 134, passing transversely into and through the second cavity 136 and located to align with the corresponding apertures 122 in the mounting block 110, when the tool holder assembly 100 is in the assembled configuration shown in Fig. 1. The transverse apertures 142 in the projection 134 may or may not be the same size as the transverse apertures 122 in the mounting block 110.

[0055] The fixed orientation cutting tool 150 has a cutting head 152 and a mounting portion 154. The mounting portion 154 of the cutting tool 150 is shaped to fit into the second cavity 136. A transverse aperture 156 is provided laterally through the mounting portion 154 and is located to align with an upper one of the corresponding transverse apertures 122, 142 in the mounting block 110 and the projection 134, when the tool holder assembly 100 is in the assembled configuration shown in Fig. 1. The transverse

aperture 156 in the mounting portion 154 may or may not be the same size as the transverse apertures 122, 142 in the mounting block 110 and projection 134.

[0056] In the embodiment depicted, the mounting portion 154 has an external shape that is substantially complementary to that of the second cavity 136 with length and width dimensions slightly smaller than the second cavity 136. These dimensions are such that the mounting portion 154 fits snugly within the second cavity 136 but with only minimal, if any, frictional interference between the components allowing the mounting portion 154 to slide into and out of the second cavity 136. In an alternative embodiment, the mounting portion 154 may be secured by interference fit within the second cavity 136. [0057] The spray device 170, shown in greater detail in Fig. 7 and Fig. 8, has a nozzle head 172 and a generally cylindrical base portion, or stem, 174. The stem 174 has a neck portion 176 between the nozzle head 172 and a radially projecting rib 178. Circumferential seal notches 175 are also provided in the stem for accommodating sealing rings on a lower portion of the stem 174. A fluid passage extends axially from the base of the stem 174 to the nozzle head 172. A threaded hole 173 is provided in the nozzle head 172 to allow different nozzles to be employed and to allow adjustment of the spray. The spray device aperture 138 in the upper portion 132 of the tool support member 130 has a shape that is complementary to an external cross-sectional shape of the nozzle head 172 of the spray device 170 and is provided in a predetermined orientation relative to the second cavity 136. This maintains the spray device 170 in the correct orientation relative to the cutting tool 150.

[0058] The spray mounting component 180 is a removable block that that is releasably securable within the spray device recess 120. The spray mounting component 180 may be secured by way of threaded screws passing through screw holes 182 and into threaded holes in the spray device recess 120. The spray mounting component 180 includes a circular first aperture 184 that extends through the spray mounting component 180 from top to bottom. The first aperture 184 narrows from an upper portion to a lower portion at an internal shoulder. The stem 174 is shaped to fit axially into the first aperture 184. A rectangular second aperture 186 extends laterally through the spray mounting component 180, transverse to the first aperture 184. When the stem 174 is inserted into the first

aperture 184, the neck portion 176 is aligned with the second aperture 186. A clip 190 is insertable into the second aperture 186 and is engageable with neck portion 176 and/or the rib 178 of the stem 174 to retain the spray device 170 in the mounting component 180.

[0059] In order to assemble the tool holder assembly 100, the mounting component 180 is secured in the spray device recess 120 by way of screws via the screw holes 182. The stem 174 of the spray device 170 is inserted into the first aperture 184 of the mounting component 180 and is oriented as desired. The spray device 170 is then secured in place by inserting the clip 190 into the second aperture 186 to engage the neck portion 176 of the stem 174.

[0060] The tool support member 130 is assembled in the mounting block 110 by inserting the projection 134 into the first cavity 118 until the upper portion 132 of the tool support member 130 abuts against the upper surface 116 of the mounting block 110. In doing so, the nozzle head 172 of the spray device 170 pokes through the spray device aperture 138. The cutting tool 150 is assembled in the mounting block 110 by inserting the mounting portion 154 of the cutting tool 150 into the second cavity 136 of the tool support member 130. The cutting tool 150 and the tool support member 130 are then secured in place by way of retaining pins, bolts, roll pins, or other fasteners passing through the respective aligned transverse apertures 122, 142, 156 in the mounting block 110, tool support member 130, and the cutting tool 150. In one embodiment, the roll pins would comprise a stainless steel inner and plastic composite outer. In another embodiment, the transverse apertures 122, 142, 156 are fitted with plastic component to reduce vibration between the tool and the retention system.

[0061] Disassembly is performed by simply reversing the process described above. In addition, the spray device 170 can be removed and replaced separately to the cutting tool 150 and tool support member 130. By removing the clip 190, the spray device 170 can be removed via the spray device aperture 138 in the tool support member 130. This allows the spray device 170 to be replaced without removing the cutting tool 150 or tool support member 130. It also allows the cutting tool 150 and/or tool support member 130 to be replaced without removing the spray device 170. Furthermore, if the first aperture 184, in which the spray device 170 is mounted is damaged by an impact to the spray device 170, the removable mounting component 180 allows the damaged spray device 170 and mounting component 180 to be replaced without replacing the mounting block 110, which would require the entire cutter drum to be removed.

[0062] The tool support member 130 is typically formed from a slightly softer material than the mounting block 110 and the cutting tool 150 is typically formed from a slightly softer material than the tool support member 130. This means that, in the event of a failure due to excessive operational forces, the cutting tool 150 is likely to fail first, followed by the support member 130, and least likely the mounting block 110. Further, as the components wear, the cutting tool 150 can be replaced most frequently, followed by the tool support member 130, and least frequently the mounting block 110. Having a replaceable support member 130, which is designed to sustain damage or fail before the mounting block 110, also means that the mounting block 110 is rarely damaged in operation and greatly reduces the frequency with which the mounting block 110 needs to be replaced or repaired.

[0063] In the embodiment depicted in Figs 1 to 8, the orientation (or tool direction) of cutting tool 150, represented by the arrow T, is offset at an acute angle, such as 15°, to the forward direction F of the mounting block 110. The orientation of the cutting tool 150 may be varied in different embodiments, such as having the tool facing directly forward or offset to the opposite side of the mounting block 110. In such embodiments, the orientation of the first and second cavities 118, 136 and the projection 134 match the orientation of the cutting tool 150.

[0064] Fig. 9 is an exploded view of an alternative embodiment of a tool holder assembly 200. The tool holder assembly 200 includes a mounting block 210, a tool support member 230 (or tool sleeve), and a fixed orientation cutting tool 250. The tool holder assembly 200 is assembled in essentially the same manner as described above with respect to the embodiment shown in Figs 1 to 8. However this embodiment includes a number of significant differences. For example, in this embodiment, a simple off-the-shelf spray device, mountable in the spray device aperture 280, is employed instead of the custom spray mounting component 180. In the embodiment depicted, the orientation of the cutting tool 250 is not offset to the forward direction F of the mounting block 210, although in other similar embodiments the cutting tool 250 may be offset, as in the embodiment of the tool holder assembly 100 shown in Figs 1 to 8 and in the embodiment depicted in Fig. 16.

Another significant difference in this embodiment is the cross-sectional shape and angle of inclination of the first cavity 218, the projection 234 of the tool support member 230, the second cavity 236, and the mounting portion 254 of the cutting tool 250, in which the cross- sectional shape resembles a bow tie shape and the components extend at a swept back angle, extending downwardly and rearwardly rather than straight down.

[0065] As depicted in isolation in Fig. 10, the mounting block 210 has a first cavity 218 having a cross-sectional profile with a shape having generally parallel sides at opposing end portions 222 and sides that taper inwardly from the opposing end portions 222 to an intermediate portion or point 224 that is narrower in cross-sectional profile than the opposing end portions 222, somewhat resembling a bow tie shape. The intermediate portion 224 may be located at the midpoint between the two end portions 222, as it is in the embodiment shown, or may be closer to one or other of the two end portions 222. The end portions 222 may be equal in width, as they are in the embodiment shown, or one end portion 222 may be wider than the other end portion 222. The cross-sectional profile may have a shape with sides at the end portions 222 that are angularly offset rather than being generally parallel, such as the rear side being more perpendicular to the direction of rotation than the front side. The cross-section of the first cavity 218 may have various other shapes such as rectangles, trapeziums, and other more complex shapes. [0066] In order to secure the cutting tool 250 and the tool support member 230 in the mounting block 210, when assembled, the mounting block 210 has a primary transverse aperture 225 and a secondary transverse aperture 227, both of which extend laterally through the sidewalls of the mounting block 210 and are adapted to receive corresponding primary and secondary retaining pins 228, 229, which secure the cutting tool 250 and tool support member 230 within the mounting block 210. The retaining pins 228, 229 may alternatively be roll pins, bolts, or other fastening devices.

[0067] Unlike the embodiment shown in Figs 1 to 8, the first cavity 218 does not extend vertically through the mounting block 210 in a direction perpendicular to the upper surface 216 and forward direction F. In this embodiment, the first cavity 218 extends at an obtuse, swept back angle Q, relative to the upper surface 216 and forward direction F, extending rearwardly as the first cavity 218 extends downward into the mounting block 210.

[0068] As depicted in isolation in Figs 11 and 12, the tool support member 230 has a second cavity 236 extending through the projection 234. The second cavity 236 has a cross- sectional profile with a shape having generally parallel sides at opposing end portions 242 and sides that taper inwardly from the opposing end portions 242 to an intermediate portion or point 244 that is narrower in cross-sectional profile than the opposing end portions 242, somewhat resembling a bow tie shape, as is most evident in Fig. 13, which is a cross- sectional view of the projection 234.

[0069] The intermediate portion 244 may be located at the midpoint between the two end portions 242 or may be closer to one or other of the two end portions 242. The end portions 242 may be equal in width or one end portion may be wider than the other end portion 242. The cross-sectional profile may have a shape with sides at the end portions 242 that are angularly offset rather than being generally parallel, such as the rear side being more perpendicular to the direction of rotation than the front side. The cross-section of the second cavity 236 may employ various other shapes such as rectangles, trapeziums, and other more complex shapes.

[0070] As shown in Fig. 13, in this embodiment, the external shape of the projection 234 has a substantially complementary shape to the cross sectional profile of the first cavity 218 of the mounting block 210, such that the projection 234 of the tool support member 230 is shaped to fit into the first cavity 218.

[0071] As best shown in Fig. 12, unlike the embodiment shown in Figs 1 to 8, the projection 234 does not extend vertically down from the upper portion 232 in a direction perpendicular to the upper surface 216 and forward direction F. In this embodiment, the projection 234 extends at an obtuse, swept back angle Q, relative to the upper surface 216 and forward direction F, extending rearwardly as the projection 234 extends downward from the upper portion 232. This is complementary to the first cavity 218 and allows the projection 234 to be inserted into the first cavity 218 by sliding the projection 234 into the first cavity 218 in a downward and rearward direction inclined at the angle Q relative to the forward direction F. Similarly, the second cavity also extends at the same obtuse, swept back angle Q, relative to the upper surface 216 and forward direction F, extending internally of, generally parallel to, and longitudinally of, the projection 234.

[0072] The tool support member 230 also has a primary transverse aperture 243 and a secondary transverse aperture 245, both of which extend laterally through the tool support member 230 and are located to align with the corresponding primary and secondary transverse apertures 225, 227 in the mounting block 210 and are also adapted to receive the primary and secondary retaining pins 228, 229, which secure the cutting tool 250 and tool support member 230 within the mounting block 210. In the embodiment depicted, the secondary transverse aperture 245 is open to the front of the projection 234. In order to accommodate the retaining pin 229, the secondary transverse aperture 227 in the mounting block 210 partially extends across the front surface of the first cavity 218, as can be seen in Fig. 10, and together with the secondary transverse aperture 245 of the tool support member 230, creates a cylindrical aperture through the tool holder assembly 200, when the tool support member 230 is assembled in the mounting block 210.

[0073] As depicted in isolation in Fig. 14, the cutting tool 250 has a cutting head 252 and a mounting portion 254. A transverse aperture 256 is provided laterally through the mounting portion 254 and is located to align with the corresponding primary transverse aperture 225 in the mounting block 210 and the primary transverse aperture 243 in the projection 234 of the tool support member 230. The transverse aperture 256 in the mounting portion 254 is adapted to receive the primary retaining pin 228, which secures the cutting tool 250 both in the tool support member 230 and in the mounting block 210.

[0074] As shown in Fig. 15, in this embodiment, the external shape of the mounting portion 254 has a substantially complementary shape to the cross sectional profile of the second cavity 236 of the support member 230, such that the mounting portion 254 of the cutting tool 250 is shaped to fit into the second cavity 236. [0075] Returning to Fig. 14, unlike the embodiment shown in Figs 1 to 8, the mounting portion 254 does not extend vertically down from the cutting head 252 in a direction perpendicular to the forward direction F. In this embodiment, the mounting portion 254 extends at an obtuse, swept back angle Q, relative to the forward direction F, extending rearwardly as the mounting portion 254 extends downward from the cutting head 252. This is complementary to the second cavity 236 and allows the mounting portion 254 to be inserted into the second cavity 236 by sliding the mounting portion 254 into the second cavity 236 in a downward and rearward direction inclined at the angle Q relative to the forward direction F.

[0076] In the embodiment of Figs 9 to 15, the bow tie shape of the projection 234, first cavity 218, mounting portion 254, and the second cavity 236, provides a greater surface area interface between the components and strengthens the components in the areas where the induced operational stresses are greatest. This allows the tool holder assembly components to have an improved operational lifespan.

[0077] Furthermore, in the embodiment of Figs 9 to 15, the obtuse angle Q of the projection 234, first cavity 218, mounting portion 254, and second cavity 236 provide greater resistance to the operational moment induced on the cutting tool 250, when in use. This provides better retention of the cutting tool 250 by providing a surface that assists to oppose the centrifugal force and bending action applied to the cutting tool 250, when in use. This inclined geometry creates lower bending/shear forces in the mounting portion 254 of the cutting tool 250 and produces less of a lifting force. This results in the cutting tool 250 being more likely to fail due to shear forces in the cutting head 252, rather than fail in the mounting portion 254 of the cutting tool 250, which can result in damage to the toolholder or can cause the mounting portion 254 to bend making it difficult to remove the cutting tool 250. This inclined geometry combined with the bow tie also results in the primary retaining pin 228 undergoing very little load during an event that will snap the pick.

[0078] This design can also improve the strength of the toolholder around the top of the spray device by providing more material between the spray device and the first cavity 218 and/or decreases the toolholder's length for a given spray device strength which allows better positioning of the toolholder on the drum, or more toolholders to be placed on the drum, or a combination of both. Preferably, the angle Q is in the range of 89° to 135° for best results. [0079] Fig. 16 is an exploded view of an alternative embodiment of a tool holder assembly 300. The tool holder assembly 300 includes a mounting block 310, a tool support member 330 (or tool sleeve), and a fixed orientation cutting tool 350. The tool holder assembly 300 is assembled in essentially the same manner as described above with respect to the earlier tool holder assembly embodiments 100, 200. However, in this embodiment the orientation (or tool direction) of cutting tool 350, represented by the arrow T, is angularly offset to the forward direction F of the mounting block 310. In this embodiment, the cutting tool 350, with the cutting head 352, mounting portion 354, and transverse aperture 356, is identical to the cutting tool 250 of the embodiment in Figs 9 to 15. However, in order to orient the cutting tool 350 in a particular offset direction, the first cavity 318, projection 334, and second cavity 336 are all offset relative to the forward direction F of the mounting block 310. One further difference in this embodiment is the orientation and location of the primary transverse apertures 325, 335 and secondary transverse apertures 327, 337, which have been reoriented to pass through the toolholder assembly 300 perpendicular to the tool direction T and the secondary transverse apertures 327, 337 have been relocated from the front of the projection 334 and first cavity 318 to the rear of the projection 334 and first cavity 318.

[0080] In all three embodiments, the cutting tool 150, 250, 350 has only a single transverse aperture 156, 256, 356, so that the cutting tool 150, 250, 350 can be removed by unfastening a single bolt or retaining pin. The cutting tool 150, 250, 350 is generally replaced more frequently than any other component and this allows the tool support member 130, 230, 330 to remain secured in the mounting block 110, 210, 310 by the other bolt or retaining pin, during replacement of the cutting tool 150, 250, 350.

[0081] The design of the present invention minimises the frequency with which the entire tool holder assembly needs to be replaced and allows individual components to be more easily replaced individually, rather than one damaged component requiring the replacement of multiple components together. The design also reduces the likelihood of the failure of one component, such as the cutting tool, causing damage to another component, such as the spray device. Accordingly, the design results in a tool holder assembly that is more reliable in operation and much easier and cheaper to maintain when components wear or fail. [0082] Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.