Tool

Abstract

A machining tool 100, possibly a dressing or broaching tool, has a body 102 with a main axis (M fig.5) and slots (104 fig.4) transverse to the main axis and between first and second opposing faces of the body (110, 112 fig.4). Abrasive segments 106 are in the slots, each abrasive segment having a mounting portion 126, for mounting the abrasive segment in the body, having a first end surface 128 and a second end surface 130 opposing the first end surface, and each abrasive segment having an abrading edge 132. The body has a first flange (114 fig.4) on the first face of the body, a second flange (116 fig.4) on the second face of the body and a compressible element (122 fig.10), such as an O-ring, in each slot and in contact with the second flange. Each abrasive segment has first and second protrusions 134, 136 and is mounted in the body such that the first end surface contacts the first flange and the second end surface contacts the compressible element.

Description

FIELD OF THE INVENTION This disclosure relates to a machining tool. In particular, this disclosure relates to a machining tool which can be used in a method of broaching or in a method of dressing a grinding wheel. BACKGROUND US2018361540A1 (US’540) discloses a rotary dressing tool. As noted in paragraph

[0026] of US’540, the rotary dressing tool 101 comprises an abrading surface 102 concentric around on a hub 103, both of which are sandwiched between a first flange 104 and a second flange 105 (see also Figures 1 and 5 of US’540). As noted in paragraph

[0044] of US’540, the abrasive segments that form the abrading surface 102 are mounted in the hub 103 by the provision of a plurality of slots in the outer circumference of the hub (see also Figures 6 and 7 of US’540). As noted in paragraph

[0042] of US’540, when the flanges 104 and 105 are placed against the hub 103, the rims 504 and 505 co-operate with the wider base of the abrasive segment to prevent radial movement of the abrasive segments (see also Figures 5 and 6 of US’540). In order to properly fit in the slot and be contained by the rims 504 and 505 of the flanges 104 and 105, all of the surfaces of abrasive segments of US’540 must be machined to an exceptionally high level of accuracy. This leads to a very' high manufacturing cost for the abrasive segments, especially where the abrasive segments are formed of a superhard material such as polycrystalline diamond (PCD) or polycrystalline cubic boron nitride (PCBN). It also increases the complexity of mounting the abrasive segments in the slots. Furthermore, the more surfaces which must be machined the greater the likelihood of imperfections, which leads to the abrasive segments being misaligned. These abrasive segments must then be trimmed before the dresser can be used, and the greater the need for trimming, the greater the cost. The machining tool as disclosed herein provides a solution to the above-mentioned problem. SUMMARY OF THE INVENTION The machining tool disclosed herein has been designed such that the configuration of the mating surfaces between the abrasive segment and the body of the tool achieves precise and repeatable positioning of the abrasive segments with respect to the rotating axis of the tool, in the case of a rotary' tool, or with respect to the direction of linear cutting motion, in the case of a linear tool. This is critical to reduce the machining allowance included on the cutting profde of the abrasive segments, which must be removed during final in-situ trimming of the assembled tool to achieve tine strict cutting profile tolerances required. This significantly reduces the machining time and costs associated with this final trimming step, which may be carried out by wire electric discharge machining or by laser ablation. As detailed herein, this design is suitable not only for rotary abrasive machining tools, such as the rotary dresser disclosed in US’540, but for any machining tool where an abrasive segment is mounted in a slot which extends between two flanges. In accordance with the invention, there is provided a machining tool comprising: a body with a mam axis and a plurality of slots extending substantially transverse to the mam axis and between a first face and a second, opposing face of the body; a plurality of abrasive segments located in the slots, each abrasive segment comprising a mounting portion for mounting the abrasive segment in the body, said mounting portion comprising a first end surface and a second end surface opposing the first end surface, and each abrasive segment further comprising an abrading edge; a first flange on the first face of the body; a second flange on the second face of the body; and a compressible element in each slot and in contact with the second flange; wherein each abrasive segment is mounted in the body such that the first end surface contacts the first flange and tire second end surface contacts the compressible element. As an option, the abrasive segment comprises first and second protrusions, wherein the first protrusion comprises the first end surface and the second protrusion comprises the second end surface. As an option, there is avoid in the slot between the first and second protrusions. As an option, the first and second protrusions contact the base of the slot. As an option, the abrasive segment does not contact the second flange. As an option, the abrasive segment further comprises a first edge portion which projects over the first flange. As an option, the first edge portion is not in contact with the first flange. As an option, the abrasive segment further comprises a second edge portion opposing the first edge portion, wherein the second edge portion projects over the second flange. As an option, the second edge portion is not in contact with the second flange. As an option, each abrasive segment is individually secured to the body using a pin element that extends at least partially through the abrasive segment and / or at least partially through the body adjacent the abrasive segment. As an option, the abrasive segment comprises a first partial aperture and the body comprises a second partial aperture, the first and second partial apertures together forming a complete aperture when the abrasive segment is in the slot and when the first and second partial apertures align. As an option, the abrasive segment comprises a first partial aperture and the body comprises a second partial aperture, wherein the radial offset between the centres of the first and second partial apertures is up to 5% of the diameter of the first partial aperture. As an option, the radial offset is up to 2% of the diameter of the first partial aperture. As an option, the radial offset is at least 0.1% of the diameter of the first partial aperture. As an option, the pin element is a coil pin, wherein the coil pin comprises an overlapping portion. As an option, the overlapping portion of the coil pin is substantially adjacent to the interface between the body and the abrasive segment. As an option, the abrasive segment further comprises a first side surface and a second side surface which opposes the first side surface. As an option, the slot has a base, a first side wall and a second side wall. As an option, the first side surface of the abrasive segment contacts the first side wall of the slot. As an option, the second side surface of the abrasive segment contacts the second side wall of the slot. As an option, the abrasive segment is not in contact with the first side wall of the slot. As an option, the first side surface of the abrasive segment is not in contact with the first side wall of the slot. As an option, the first partial aperture is formed in the face of the abrasive segment which comprises the first side surface of the abrasive segment. As an option, the first and / or second flanges are formed from a plate(s) attached to the body. As an option, the abrasive segment comprises a superhard material. As an option, the abrasive segment further comprises a carbide substrate adjoining the superhard material at an interface. As an option, the interface is located off-centre with respect to a centreline of the abrasive segment. As an option, the superhard material comprises poly crystalline diamond (PCD). As an option, the superhard material comprises poly crystalline boron nitride (PCBN). As an option, the body is a hub of a rotary abrasive machining tool; and the hub has a longitudinal axis of rotation substantially perpendicular to the main axis. As an option, the body is a hub of a rotarv abrasive machining tool; the hub has a longitudinal axis of rotation substantially perpendicular to the main axis; and the compressible element is circumferential. The present disclosure further provides a use of the machining tool as described herein in a method of broaching. The present disclosure further provides a use of the machining tool as described herein in a method of dressing a grinding wheel. BRIEF DESC1PT1ON OF THE DRAWINGS The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is an isometric projection of a first embodiment of a machining tool; Figure 2 is an end view of the tool of Figure 1; Figure 3 is an isometric projection of the hub of the machining tool of Figure 1; Figure 4 is an exploded isometric projection shown in section of the tool of Figure 1; Figure 5 is a front view of the tool of Figure 1; Figure 6 is an isometric projection of an embodiment of an abrasive segment; Figure 7 is an isometric projection of another embodiment of an abrasive segment; Figures 8a and 8b show front and back views of the abrasive segment of Figure 6; Figure 9 is a cross-sectional view taken through the line A-A of Figure 5; Figure 10 is an enlarged view of encircled zone B from Figure 9; Figure 11 is an enlarged view of encircled zone C from Figure 10; Figure 12 is an enlarged view of encircled zone D from Figure 10; Figure 13 is a front view of the tool of Figure 1. showing zone E; Figure 14 is an enlarged view of encircled zone E from Figure 13; Figure 15 is a schematic view of an embodiment in which tire partial apertures in the hub and the abrasive segment are radially offset; Figures 16a and 16b show two possible orientations of the coil pin; Figure 17 is an isometric projection of a second embodiment of a second machining tool; and Figure 18 is an exploded isometric projection of tine tool of Figure 17; and Figure 19 is a lateral cross-sectional view through an embodiment of the abrasive segment and shows a layer of polycrystalline diamond (PCD) mounted on a carbide substrate. DETAILED DESCTIPION Referring to Figures 1 to 16, a first embodiment of a machining tool is indicated generally at 100. The machining tool in this embodiment is a rotary abrasive machining tool. The rotary abrasive machining tool 100 comprises a hub 102 with a plurality of axially extending radial slots 104 (best seen in Figure 3) in an outer circumference thereof, and a plurality of abrasive segments 106 located in the radial slots 104. The hub 102 is annular with a central aperture 108 for mounting onto the rotatable shaft of a rotary dressing assembly (not shown). The general shape of the hub 102 is akin to a pipe flange, in that it has a ring portion and a raised surface to one side, best seen in Figure 3. The hub 102 has a longitudinal axis of rotation L which passes through the centre of the central aperture 108 (as shown in Figure 4) and a main axis M perpendicular to the longitudinal axis of rotation (as shown in Figure 5). The radial slots 104 are therefore substantially transverse to the main axis M. The hub 102 has a first face 110 and a second face 112 opposing the first face 110 (shown in Figure 4). Tire slots 104 extend axially between the first face 110 and the second face 112 of the hub 102. The slots 104 also extend radially into the hub 102, thereby defining a series of supports 146 between the slots 104 (see Figure 3). These supports may also be termed the first and second side walls of the slots. While the abrasive segment 106 may be mounted such that it is in contact with supports 146 on each side (or, phrased alternately, in contact with the first and second side walls of the slot), it can be advantageous to mount the abrasive segment 106 so that only one side is in contact with a support 146 - this is explained in detail later. A first plate 114 and a second plate 116 are attached to the first face 110 and the second face 112, respectively. The plates 114, 116 are attached so as to form a circumferential protruding lip, or a flange, on the front and back of the machining tool 100. As can be seen in Figure 4, the plates 114, 116 are secured in place using a plurality of screws 118 and threaded holes 120 provided in the hub 102, spaced apart from the abrasive segments 106. As will be explained in more detail later, the flanges formed by the plates 114, 116 work in combination with a compressible element 122 to prevent axial movement of the abrasive segments 106 under standard operating conditions. It should be noted that, while in this embodiment the flanges are formed by the attachment of plates 114, 116 to the hub 102, an alternative construction where one or both of the flanges is integrally formed with the hub 102 is also part of the present disclosure. One or both plates 114, 116 may have a patterned surface, and the corresponding face(s) 110, 112 of the hub 102 may have a corresponding pattern which engages with the pattern on the respective plate in a mating arrangement. The cooperating patterns minimise relative rotation between the hub 102 and the plate. The pattern may be a series of recesses and / or protrusions. In this embodiment, the plates 114, 116 and the hub 102 comprise throughholes 124 to allow them to be connected to other rotary abrasive machining tools to form a dresser stack (see Figures 3 and 5). Where the rotary abrasive machining tool is not used in a dresser stack, these throughholes 124 can be omitted. An isometric projection view of the abrasive segment 106 of the present embodiment is shown in Figure 6, with accompanying front and back views in Figures 8a and 8b, respectively. Abrasive segment 106 comprises a mounting portion 126 for mounting the abrasive segment 106 in the hub 102. Hie mounting portion 126 comprises a first end surface 128 and a second end surface 130 opposing the first end surface 128. The abrasive segment 106 further comprises an abrading edge 132. The exact profile of the abrading edge 132 can be altered depending on the nature of the item to be machined. For example, if the rotary abrasive machining tool is for dressing of grinding wheels having profiles of complex geometry, such as fir-tree profiles, then an abrading edge as shown in Figs. 4A and 4B and described in paragraph

[0032] of US’540 may be used. In this embodiment, the abrasive segment 106 comprises first and second protrusions 134, 136. The first protrusion 134 comprises the above-mentioned first end surface 128, and the second protrusion 136 comprises the above-mentioned second end surface 130. The abrasive segment further comprises first and second side surfaces 160, 170. When mounted in the hub 102, second side surface 170 contacts adjacent support 146 (second side surface 170 is depicted m Figure 8b). In other words, second side surface 170 is in contact with the second side wall of the slot. However, first side surface 160 does not contact a support 146 (in other words, first side surface 160 is not in contact with the first side wall of the slot); rather, first side surface 160 contacts a pin element 142, which is described in more detail below. In this embodiment, the abrasive segment 106 has a generally L-shaped profile. The abrasive segment 106 comprises a first segment leg portion 138 extending from a second segment leg portion 140, as indicated in Figure 6. However, this is not necessary for all applications, and for example, the upwardly-extending arm of the L could be omitted, as depicted in Figure 7 which shows the abrasive segment 206. Abrasive segment 206 is in all other ways identical to abrasive segment 106. In this embodiment, each abrasive segment 106 is individually secured to the hub 102 using a pin element 142 that extends axially, partially through the abrasive segment 106 and partially through the hub 102 adjacent the abrasive segment 106 - as described in further detail below. The half-aperture 144 on the abrasive segment for receiving the pin element 142 can be seen in Figures 6, 7 and 8a. In this embodiment, as each abrasive segment 106 is generally L-shaped, each support 146 is also generally L-shaped with a first support leg portion that extends radially and a second support leg portion that extends axially. Each abrasive segment 106 is inserted into a slot 104, in between two supports 146. Once in its final position, the first segment leg portion aligns with the first support leg portion of the hub, and the second segment leg portion aligns with the second support leg portion. The L-shaped configuration of the supports 146 helps to minimise the mass of the hub, providing support only where it is needed. If the abrasive segment w as shaped differently, for example as in abrasive segment 206 depicted in Figure 7, then the shape of the supports would be adjusted accordingly. The L-shaped configuration of the first embodiment makes the resulting rotary abrasive machining tool particularly suitable for machining fir-tree profiles. The L-shape helps to minimise the volume of material required in the abrasive segment for the machining operation. This is especially important when more expensive superhard materials such as PCD or PCBN are required for maximum wear resistance and prolonged service life. A compressible element 122, in this case an O-ring formed of an elastomer, is placed in the slots 104 in contact with the second plate 116 (see Figures 4, 10 and 11, in particular). A channel is provided in the hub itself to accommodate the O-ring. While an O-ring is used in this embodiment, other shapes of elastomer, such as flat strips or strips with a polygonal crosssection, could be used instead. While in this embodiment, the same compressible element 122, i.e. the O-ring, is used in all slots 104, an alternative construction in which a separate compressible element 122 is used in each slot 104 is also part of the present disclosure. In this embodiment, it would not be necessary to provide channels in the hub 102 itself for the compressible element 122. In a further alternative construction, there are multiple compressible elements 122 which each cover a number of slots 104. For example, if the hub 102 comprised 80 slots, it may that there are four compressible elements 122, each of which occupies 20 slots. While the compressible element 122 of the first embodiment is an O-ring, other compressible elements 122 are also contemplated as part of the disclosure. For example, flange seals, axial face seals, gaskets, press-in-place (PIP) seals, composite sealing plates (i.e. where the plate and seal are pre-bonded together as a composite) and U-cup seals may also be used. As noted above, the compressible element may be formed of an elastomer. For example, the elastomer may be or comprise a synthetic rubber. An example of a synthetic rubber is a thermoset. Thermosets include butadiene rubber, butyl rubber, chlorosulfonated polyethylene, epichlorohydrin rubber, ethylene propylene diene monomer, ethylene propylene rubber, fluoroelastomer, nitrile rubber, perfluoroelastomer, polyacrylate rubber, neoprene, polyisopropene, polysulfide rubber, polytetrafluoroethylene, silicone rubber and styrene butadiene rubber. The compressible element may be or comprise a thermoplastic. For example, the thermoplastic elastomer may be selected from the group consisting of styrenic block copolymers, thermoplastic polyolefmelastomers, thermoplastic vulcanizates, thermoplastic polyurethanes, thermoplastic copolyester, and thermoplastic polyamides. For example, the thermoplastic elastomer may be a polyurethane or a polyester such as polylactic acid. The elastomer may also comprise a nylon or cork material. In a further embodiment, the compressible element may be a metal or alloy, such as copper, lead or bronze, for example in the form of a wire or a strip. The mounting of the abrasive segment 106 in the slot 104 is depicted in Figures 9 to 12. The abrasive segment 106 is mounted in the hub 102 such that the first end surface 128, which is part of the first protrusion 134, contacts the first plate 114 (i.e. flange) and the second end surface 130, which is part of the second protrusion 136, contacts the compressible element 122. The first and second protrusions 134, 136 contact the base of the slot 104. There is a void V in the slot 104 between the first and second protrusions 134, 136. There is further contact between the second side surface 170 of the abrasive segment 106 and the adjacent support 146 (or, in other words, there is further contact betw een the second side surface 170 of the abrasive segment and the second side wall of the slot). As shown in Figure 11, in this embodiment, the abrasive segment 106 does not contact the second plate 116. The abrasive segment further comprises a second edge portion 148 which projects over, but does not contact, the second plate 116. As shown in Figure 12, in this embodiment, the abrasive segment 106 does contact the first plate 114. The abrasive segment 106 further comprises a first edge portion 150 which projects over, but does not contact, the first plate 114. The first and second edge portions 148, 150 are included to increase the abrasive profile length without increasing the overall length of the dresser. Without these first and second edge portions, the first and second plates 112, 114 would contribute to the total length of the assembly and the tool may be too long to fit in the machine. In this design (i.e. that depicted in Figures 9-12), movement of the abrasive segments relative to the slot 104 is constrained by having ‘hard-touch’ mating surfaces as detailed above which have been engineered to ensure repeatable locating of the abrasive segment within the hub and reduce geometric variation of the cutting edge profile across the different segments. Specifically, the following ‘hard-touch’ mating surfaces have been incorporated in the design to provide datum positioning in the respective axes: (1) “hard touch” between the first end surface 128 and the first plate 114; (2) “hard touch” between the base of the first protrusion 134 and the base of the slot 104; (3) “hard touch” between the base of the second protrusion 136 and the base of the slot 104;and (4) “hard touch” between the second side surface 170 of the abrasive segment and the adjacent support 146 (or, in other words, the second side wall of the slot). In the axial direction, the ‘hard-touch’ contact is restricted to a single axial direction (i.e. that provided by the contact between the first plate and the first end surface of the abrasive segment). Uns is important as including a second axial ‘hard-touch’ contact between the second plate and the abrasive segment would cause distortion of (and possible damage to) the segment resulting from axial compression of the segment as it is clamped between the two side plates. This is a particular problem when the abrasive segment comprises PCD. This clamping load would also vary depending on the length tolerance of each abrasive segment, causing variable levels of compression and distortion for each individual abrasive segment. To avoid this problem and continue to provide resistance to axial segment movement within the hub slot two ‘soft-touch’ contact surfaces are included in the design in the form of the compressible element 122, which in this embodiment is an O-ring, and coil pin 142, which also functions as a compressible element. These compressible elements accommodate variability in the segment length and width and provide additional resistance to axial segment movement within the slot. Importantly, this is achieved without introducing possible distortion problems of the abrasive segment. As a further advantage, the compressible element provides vibration damping to the abrasive segment. In addition, if the load provided by the compressible element 122 is of a similar order of magnitude to that developed by the frictional contact due to the coil pin assembly, then the load provided by the compressible element 122 would ensure that the segment was located (or seated) properly against the axial hard touch surface following assembly. While in this embodiment two “soft-touch” contact surfaces are provided, an embodiment in which there is only one “soft-touch” contact surface, i.e. where both side surfaces 160, 170 of the abrasive segment are in contact with respective adjacent side walls of the slot, providing an additional “hard touch” between first side surface 160 and support 146 (i.e. the first side wall of the slot) in place of the “soft touch” between first side surface 160 and coil pin 142, is also included in this disclosure. This represents an improvement in respect of prior art designs without any “soft touches” but requires more precise machining of first side surface 160 and the first side wall of the slot than the above embodiment with two “soft touch” contact surfaces. As a further advantage, the requirement for precision machining of the abrasive segment is limited to the “hard touch” surfaces listed above. Tolerances for the remainder of the surface of the abrasive segment can be less precise. This makes manufacture of the abrasive segments, for example by cutting them from a PCD blank using laser ablation or electrical discharge machining, a less costly and time-consuming activity. It also facilitates mounting of the abrasive segments in the slots. As depicted in Figures 13 to 16, in this embodiment each abrasive segment 106 is individually secured to the hub 102 using a pin element 142 that extends partially through the abrasive segment 106 and partially through the hub 102 adjacent the abrasive segment 106. As can be seen in Figures 15 and 16, there is a void between the abrasive segment 106 and the hub 102 on the side of the abrasive segment where the pin element 142 is inserted. The abrasive segment 106 can be removed from the hub 102 simply by withdrawing the pin element 142 and the compressible element 122. The pin element 142 may be made from steel, or any of the materials listed above in the context of the compressible element. As one option, the abrasive segment 106 comprises a first partial aperture 144 and the hub comprises a second partial aperture 152, the first and second partial apertures 144, 152 together forming a complete aperture when the abrasive segment 106 is in the slot 104 and when the first and second partial apertures 144, 152 align. However, it has been found that when tire abrasive segment 106 comprises a first partial aperture 144 and the hub 102 comprises a second partial aperture 152, wherein the radial offset between the centres of the first and second partial apertures 144, 152 is up to 5% of the diameter of the first partial aperture 144, then the connection is improved. In the example shown, the radial offset is approximately 2% of the diameter of the first partial aperture 144. Tire offset assists, along with hard and soft touch surfaces detailed above, in locating mating surfaces of the slot base and the protrusions 134, 136 with repeatable accuracy. Furthermore, it has been found that it is particularly advantageous when the pin element 142 is a coil pin, wherein the coil pin comprises an overlapping portion, and wherein the overlapping portion of the coil pin is substantially adjacent to the interface between the hub 102 and the abrasive segment 106, as depicted in Figures 15 and 16a. This is because the orientations shown in Figures 15 and 16a provide higher frictional holding force due to a larger effective pin diameter, E, compared to the orientation shown in Figure 16b. The rotary abrasive machining tool may be configured as a grinding wheel, a rotary dressing tool or any other similar form of machining tool. As mentioned previously, the rotary abrasive machining tool is particularly useful for the dressing of grinding wheels having profiles of complex geometry, such as fir-tree profiles. While this improved method of mounting the abrasive segment in the hub has been exemplified above in the context of a rotary abrasive machining tool, it is not limited to such an application. As shown in Figures 17 and 18, the same method of mounting can be deployed in linear abrasive machining tools such as a broaching tool, where the annular hub 102 is replaced with a linear body 202. Referring to Figures 17 and 18, a second embodiment of a machining tool is indicated generally at 200. The machining tool in this embodiment is a linear abrasive machining tool, suitable, for example, for broaching applications. The linear abrasive machining tool 200 comprises a body 202 with a plurality of radial slots 204 (best seen in Figure 18) and a plurality of abrasive segments 306 located in the radial slots 204. The body 202 has a main axis M along its length. The slots 204 are therefore substantially transverse to the main axis M. The body 202 has a first face 210 and a second face 212 opposing the first face 210 (shown in Figure 18). The transverse slots 204 extend between the first face 210 and the second face 212. To these faces 210, 212 are attached a first plate 214 and a second plate 216, respectively. Hie plates 214, 216 are attached so as to form a peripheral protruding lip, or a flange, on the front and back of the machining tool 200. As can be seen in Figure 18 the plates 214, 216 are secured in place using a plurality of screws 218 and threaded holes 220 provided in the body 202, spaced apart from the abrasive segments 306. As explained above in the context of the first embodiment but equally applicable here, the flanges formed by the plates 214, 216 work in combination with a compressible element 222 to prevent transverse movement of the abrasive segments 206 in standard operating conditions. It should be noted that, while in this embodiment the flanges are formed by the attachment of plates 214, 216 to the body 202, an alternative construction where one or both of the flanges is integrally formed with the body 202 is also part of the present disclosure. As noted above in the context of the first embodiment, one or both plates 214, 216 may have a patterned surface, and the corresponding face(s) 210, 212 of the body 202 may have a corresponding pattern which engages with the pattern on the respective plate in a mating arrangement. Abrasive segment 306 is of principally the same design as abrasive segment 106. The major differences are that abrasive segment 306 does not comprise a L-shaped support and that the abrading edge 332 is substantially planar. Note, however, that the abrading edge could be provided with any suitable profile depending on the particular machining application in which the tool is to be deployed. Otherwise, abrasive segment 306 has the same parts and is mounted in the slot 204 in tire same way as abrasive segment 106 as detailed in the description of the first embodiment above. This includes use of a pin element 242 which extends partially through the abrasive segment 306 and partially through the body 202 adjacent the abrasive segment 306. The half-aperture 244 on the abrasive segment for receiving the pin element 242 can be seen in Figure 18. As described above in the context of the first embodiment, the slots extend into the body 202, thereby defining a series of supports 246 between the slots 204. For each slot 204, there is an adjacent support 246. Each abrasive segment 306 is inserted into a slot 204, in between two supports 246. The mounting of the abrasive segment 306 in the slot 204 is analogous to that detailed above in the context of Figures 9-16 of the rotary abrasive machining tool and provides the same advantages. It should be noted that where the above description refers to “radial” in the context of a rotary tool, the term “normal” should be substituted when considering the linear tool, and where the above description refers to “axial” in the context of a rotary tool, the term “transverse” should be substituted when considering the linear tool. The transverse t and normal n directions relative to the main axis M are indicated in Figure 17. A compressible element 222, in this case a strip formed of an elastomer, is placed in the slots 204 in contact with the second plate 216. The compressible element may be formed of any of the materials as detailed above in the context of the first embodiment. A channel is provided in the body itself to accommodate the strip. As noted in the context of the first embodiment, an alternative construction in which a separate compressible element 222 is used in each slot 204 is also part of the present disclosure. In this embodiment, it would not be necessary to provide channels in the body 202 itself for the compressible element 222. In a further alternative construction, there are multiple compressible elements 222 which each cover a number of slots 204. For example, if the body 202 comprised 10 slots, it may that there are two compressible elements 222, each of which occupies 5 slots. For each of the various tool embodiments described above, each abrasive segment 106 preferably comprises PCD. The PCD may be provided as a layer having a thickness in the range of 1 to 3 mm. PCBN may also be used, though PCD is typically preferred due to its superior wear resistance properties due to its extreme hardness. Optionally, and as depicted in Figure 19, the abrasive segment comprises a carbide substrate 504 which adjoins the layer 500 of PCD at an interface. Advantageously, the interface is positioned off-centre with respect to the centreline of the abrasive segment 106, 206, 306. In other words, the interface should not align with the centreline, but rather the centreline should coincide with the PCD layer 500 of the abrasive segment 106, 206, 306. This ensures that the geometry on the cutting edge is preserved and wear begins on the PCD layer. In practice, the location of the interface relative to the centreline of the abrasive segment 106, 206, 306 is achieved by altering the proportion of PCD layer 500 to carbide layer 504. Preferably, a total thickness of the abrasive segment 106,206, 306 (i.e. PCD and, if present, also the carbide layer) is less than 5 mm, and it is more preferably less than 4 mm. Preferably, the ratio of PCD layer to carbide, if present, is in the ratio of 1 to 3. While this invention has been particularly shown and described with reference to embodiments, it will be understood by those skilled in the art that various changes m form and detail may be made without departing from the scope of the invention as defined by the appended claims.

Claims

1. A machining tool comprising:a body with a main axis and a plurality of slots extending substantially transverse to the main axis and between a first face and a second, opposing face of the body;5 a plurality of abrasive segments located in the slots, each abrasive segment comprising a mounting portion for mounting the abrasive segment in the body, said mounting portion comprising a first end surface and a second end surface opposing the first end surface, and each abrasive segment further comprising an abrading edge;a first flange on the first face of the body;10 a second flange on the second face of the body; anda compressible element in each slot and in contact with the second flange;wherein each abrasive segment is mounted in the body such that the first end surface contacts the first flange and the second end surface contacts the compressible element;wherein each abrasive segment is individually secured to the body using a pin element that 15 extends at least partially through the abrasive segment and / or at least partially through the body adjacent the abrasive segment.

2. Tire machining tool of claim 1, wherein the abrasive segment comprises first and second protrusions, wherein the first protrusion comprises the first end surface and the second protrusion comprises the second end surface.20 3. Tire machining tool of claim 2, wherein there is a void in the slot between the first andsecond protrusions.

4. The machining tool of claim 2 or claim 3, wherein the first and second protrusions contact the base of the slot.

5. The machining tool of any one of the preceding claims, wherein the abrasive segment 25 does not contact the second flange.

6. The machining tool of any one of the preceding claims, wherein the abrasive segment further comprises a first edge portion which projects over the first flange.

7. The machining tool of claim 6, wherein the first edge portion is not in contact with the first flange.30 8. The machining tool of any one of the preceding claims, wherein the abrasive segmentfurther comprises a second edge portion opposing the first edge portion, wherein the second edge portion projects over the second flange.

9. The machining tool of claim 8, wherein the second edge portion is not in contact with the second flange.

10. The machining tool of any one of the preceding claims, wherein the abrasive segment comprises a first partial aperture and the body comprises a second partial aperture, the first and second partial apertures together forming a complete aperture when the abrasive segment is in the slot and when the first and second partial apertures align.5 11. Tire machining tool of any one of claims 1 to 9, wherein the abrasive segment comprisesa first partial aperture and the body comprises a second partial aperture, wherein the radial offset between the centres of the first and second partial apertures is up to 5% of the diameter of the first partial aperture.

12. The machining tool of claim 11, wherein the radial offset is up to 2% of the diameter 10 of the first partial aperture.

13. The machining tool of claim 11 or claim 12, wherein the radial offset is at least 0.1% of the diameter of the first partial aperture.

14. The machining tool of any one of the preceding claims, wherein the pin element is a coil pin, wherein the coil pin comprises an overlapping portion.15 15. The machining tool of claim 14, wherein the overlapping portion of the coil pin issubstantially adjacent to the interface between the body and the abrasive segment.

16. The machining tool of any one of the preceding claims, wherein the first and / or second flanges are formed from a plate(s) attached to the body.

17. The machining tool of any one of the preceding claims, wherein the abrasive segment 20 comprises a superhard material.

18. The machining tool of claim 17, wherein the abrasive segment further comprises a carbide substrate adjoining the superhard material at an interface.

19. The machining tool of claim 18, wherein the interface is located off-centre with respect to a centreline of the abrasive segment.25 20. The machining tool of any one of claims 17 to 19, wherein the superhard materialcomprises polycrystalline diamond (PCD) or polycrystalline boron nitride (PCBN).

21. The machining tool of any one of the preceding claims, wherein the abrasive segment further comprises a first side surface and a second side surface which opposes the first side surface, the slot has a first side wall and a second side wall, the second side surface 30 of the abrasive segment contacts the second side wall of the slot, and the abrasivesegment is not in contact with the first side wall of the slot.

22. The machining tool of any one of the preceding claims, wherein:the body is a hub of a rotary abrasive machining tool;the hub has a longitudinal axis of rotation substantially perpendicular to the main axis; andthe compressible element is circumferential.

23. Use of the machining tool of any one of the preceding claims in a method of broaching.

24. Use of the machining tool of any one of claims 1 to 22 in a method of dressing a grinding wheel.LDCM

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