Support structure for two-sided abrasive tool and the like and method of assembling same

Abstract: A support structure such as a two-sided abrasive tool includes a first sheet with perforations having a front surface and a back surface and a second sheet with perforation having a front surface and a back surface. For an abrasive tool, a first layer of abrasive grains is bonded to the front surface of the first perforated sheet and a second layer of abrasive grains is bonded to the front surface of the second perforated sheet. Each perforation in the first sheet and the second sheet has a portion adjacent to the front surface of the sheet that is wider than a portion of the perforation that is adjacent to the back surface of the sheet. A core made of a first material is formed between the back surface of the first sheet and the back surface of the second sheet and within the perforations to anchor the first sheet and the second sheet to the core. Molded features may be disposed on the front surfaces of the sheets and integrally formed with the core through perforations in the sheets. The support structure may be used in a horizontal base or an end-of-arm tool.

Description: Background of the Invention This is a continuation-in-part of serial no. 09/374,339, filed on August 13, 1999, which is a continuation-in-part of serial no. 09/212,113, filed on December 15, 1998. This invention relates to an abrasive tool, and in particular, a tool with two abrasive sides bonded to a core which is described in US 4674237 to be considered as closest state of the art. Support structures used in various industrial applications are designed to maximize rigidity and stiffness and to minimize weight of materials, production costs and difficulty of manufacture and assembly. Such a support structure may be an abrasive tool used to sharpen, grind, hone, lap or debur a work piece or substrate of hard material, e.g., a knife. Such an abrasive tool may have a surface coated with abrasive grains such as diamond particles. An abrasive tool having an abrasive surface with depressions, e.g., an interrupted cut pattern, is known to be effective for chip clearing when applied to various work pieces. Abrasive tools must be rigid and durable for many commercial and industrial applications. Summary of the Invention According to claim 1 the invention features an abrasive tool, including a first perforated sheet having a front surface and a back surface, and a second perforated sheet having a front surface and a back surface. A first layer of abrasive grains is bonded to the front surface of the first perforated sheet and a second layer of abrasive grains bonded to the front surface of the second perforated sheet. A core is made of a first material, the core having a first surface and a second surface, the back surface of the first perforated sheet disposed adjacent to the first surface of the core and the back surface of the second perforated sheet disposed adjacent to the second surface of the core, the core being bonded to the first perforated sheet and the second perforated sheet by forming the core between the first perforated sheet and the second perforated sheet. Implementations of the invention may include one or more of the following features. The core may be formed between the first perforated sheet and the second perforated sheet by injection molding, casting or laminating. The first material may include a plastic material, which may be a glass filled polycarbonate composite. The first material may include resin, epoxy or a cementitious material. The first and second perforated sheets may have perforations that are counterbored or bevelled such that a portion of each of the perforations adjacent to the front surfaces of the sheets is wider than a portion of each of the perforations that is adjacent to the back surfaces of the sheets. The first material may be disposed within the counterbored or bevelled perforations to anchor the perforated sheets to the core. The first and second perforated sheets may have perforations arranged to form an interrupted cut pattern. The first and second perforated sheets may have perforations in a portion less than the entirety of the sheets. The first and second layers of abrasive grains may be bonded to the front surfaces of the first and second perforated sheets respectively by a plating material. The first and second layers of abrasive grains may have different degrees of abrasiveness. The tool may be a file or a whetstone. According to claim 22 the invention features a method of assembling an abrasive tool. A first perforated sheet having a front surface and a back surface and perforations therein, and a second perforated sheet having a front surface and a back surface and perforations therein, are provided. The back surfaces of the first and second perforated sheets are oriented to be spaced apart from and facing each other. A core is formed between the spaced apart back surfaces of the first and second perforated sheets. A first layer of abrasive grains is bonded to the front surface of the first perforated sheet, and a second layer of abrasive grains is bonded to the front surface of the second perforated sheet. Implementations of the invention may include one or more of the following features. The core may be formed by injecting a first material between the spaced apart back surfaces of the first and second perforated sheets, and the first material is hardened. The first material injected between the spaced apart back surfaces of the first and second perforated sheets may flow into the perforations in the first and second perforated sheets. The core may also be formed by casting or laminating. The orienting step may include placing the first and second perforated sheets into a mold. The method may also include grinding the front surfaces of the first and second perforated sheets. The bonding of the first and second layers of abrasive grains to the front surfaces of the first and second perforated sheets respectively may include electroplating, anodizing or brazing. According to an embodiment the invention features an abrasive tool, including a first perforated sheet having a front surface and a back surface and a second perforated sheet having a front surface and a back surface. A first layer of abrasive grains is bonded to the front surface of the first perforated sheet, and a second layer of abrasive grains bonded to the front surface of the second perforated sheet. A core is made of a first material, the core including a first wall having an inner surface and an outer surface, a second wall having an inner surface and an outer surface, and a plurality of walls each connected to both the inner surface of the first wall and the inner surface of the second wall to space the first wall from the second wall and to form a plurality of hollow spaces within the core. The back surface of the first perforated sheet is disposed adjacent to the outer surface of the first wall, and the back surface of the second perforated sheet is disposed adjacent to the outer surface of the second wall. The core is bonded to the first perforated sheet and the second perforated sheet by forming the core between the first perforated sheet and the second perforated sheet. Implementations of the invention may also include the following feature. The plurality of walls may form the plurality of hollow spaces along an edge of the abrasive tool. An advantage of the present invention is the ease and simplicity of using injection molding to form the core for the abrasive tool. Another advantage of the present invention is the strength, durability, and dimensional stability of the abrasive tool, which allows for selection from a wide range of materials. Another advantage of the present invention is the high strength-to-weight ratios of the composite material used to form the abrasive tool compared to any of the construction materials singularly. Another advantage of the present invention is the economies of scale that can be achieved by fabricating a single tool with multiple abrasive surfaces. A further advantage is the versatility of the abrasive tool, which may have varying shapes, uses and different grades of abrasiveness for each of the surfaces. Other features and advantages of the invention will become apparent from the following detailed description, and from the claims. Brief Description of the Drawings Fig. 1 is a diagrammatic, sectional side view of a file constructed according to the present invention. Fig. 2 is a diagrammatic plan view of the upper surface of the file of Fig. 1. Fig. 3 is a diagrammatic plan view of an alternate embodiment of the upper surface of the file of Figs. 1 and 2 which is perforated only over a portion of its abrasive surface. Figs. 4A-4C show diagrammatic, fragmentary cross-sectional views of anchoring members in the sheets used to construct a file according to the present invention. Fig. 5 is a diagrammatic, sectional side view of a mold for constructing a file according to the present invention. Fig. 6 is a flow chart showing a method of assembling an abrasive tool according to the present invention. Fig. 7 is a diagrammatic, sectional side view of a support structure constructed according to the present invention. Fig. 8 is a diagrammatic perspective view of an end-of-arm tool constructed according to the present invention. Fig. 9 is a diagrammatic perspective view of a horizontal base constructed according to the present invention. Fig. 10 is a diagrammatic, fragmentary cross-sectional view of stud anchoring members used to construct a file according to the present invention. Fig. 11 is a diagrammatic, fragmentary cross-sectional view of a perforated sheet brazed to an unperforated sheet used as an anchoring member in constructing a file according to the present invention. Fig. 12 is a diagrammatic plan view of an expanded metal sheet which may be used as an anchoring member in constructing a file according to the present invention. Fig. 13 is a diagrammatic side view of a file constructed according to an alternate embodiment of the present invention. Fig. 14 is a diagrammatic cross-sectional view of the file of Fig. 13. Fig. 15 is a diagrammatic sectional view of the top of the file of Fig. 13 along plane A-A as indicated in Fig. 14. Description of the Preferred Embodiments As shown in Fig. 7, a support structure 300 according to the present invention includes a core 302 formed between two sheets 304, 306. The formation and features of support structure 300 are described below with respect to the use of the support structure in an abrasive tool such as a hand-held file 100, as shown in Figs. 1, 2 and 3. Such an abrasive tool may also be, e.g., a whetstone, a grinding wheel or a slip stone. An abrasive tool according to the present invention includes a core formed between two sheets, with abrasive grains being bonded to the sheets to form abrasive surfaces. File 100 includes a core 110 having a first surface 180 and a second surface 182, and sheets 116, 122. Sheets 116, 122 have front surfaces 118, 124 and back surfaces 120, 126, respectively. File 100 may also include a lateral projection 130 integrally formed with core 110, to which a handle 132 or other support structure may be attached. Sheets 116, 122 are preferably made from a hard metal such as steel, but may be made of any metal, e.g., stainless steel or aluminum. Further, sheets 116, 122 may be made of a magnetic material. Depending on the type of metal used to make the sheets, the sheets or the finished abrasive tool may be magnetically clamped during processing, i.e. injection molding or grinding, or in use. Sheets 116, 122 may contain perforations, e.g., round holes 128, extending through sheets 116, 122. The perforations may have any shape, e.g., square, circular, or diamond shaped holes. Further, sheets 116, 122 may have any shape, e.g., flat, round, conical or curved. As seen in Figs. 4A-4C, the perforations are preferably bevelled or counterbored holes which form anchoring members to anchor sheets 516a-516c to the core. The bevelled counterbored holes may have a variety of different configurations. Fig. 4A shows a beveled hole 528a in sheet 516a. Figs. 4B and 4C both show stepped counterbored holes 528b and 528c, with hole 528c having projections 550. Other bevelled or counterbored configurations perform the same function. The essential feature of such a bevelled or counterbored hole is that some portion of the perforation that is closer to the front surface of the sheet is broader or wider, in a plane parallel to the sheet, than at least some portion of the perforation that is closer to the back surface of the sheet. A pattern of perforations is known as an interrupted cut pattern. As illustrated in Fig. 2, a preferred embodiment of the present invention has an interrupted cut pattern with sheets for which 40% of the surface area has been cut out for the perforations. In an alternate embodiment, only a portion of each of sheets 116, 122 contains perforations, while the remainder contains no perforations (Fig. 3). Any arbitrary portion of sheets 116, 122 may contain perforations to form an interrupted cut pattern, such that the majority of the area of each sheets forms a continuous surface. The sheets may also be anchored to the core with other types of anchoring members. As shown in Fig. 10, such anchoring members may have the form of metal studs 602 welded to the back surfaces 608, 610 of (unperforated) sheets 604, 605 prior to forming core 606 between the sheets. As shown in Fig. 11, the anchor member may be perforated metal sheets 620, 622 attached by brazing to the back surfaces 608, 610 of (unperforated) sheets 604, 605 prior to forming core 606 between the sheets. In this case, the perforations are preferably bevelled or counterbored holes, as described above with respect to Figs. 4A-4C. Alternatively, as shown in Fig. 12, an expanded metal sheet 628, formed by making slits in and then stretching or expanding a metal sheet, can be attached by brazing to the back surfaces 608, 610 of (unperforated) sheets 604, 605 prior to forming core 606 between the sheets. For the alternative anchoring members shown in Figs. 10-12, the essential feature is that the core can form around projections, i.e., studs 602, or within a crevice, i.e., the perforations in sheets 620, 622 or the open areas in expanded metal sheet 628, to anchor the core to the sheets. The back surfaces 120, 126 of sheets 116, 122, respectively, are bonded to the first and second surfaces 180, 182 of core 110, which is formed between sheets 116, 122. Core 110 may be formed by injection molding, casting or laminating. Core 110 is preferably made from a plastic material, preferably a glass filled polycarbonate composite (e.g., 40% glass filled polycarbonate). Such a composite material has an inherently higher strength to weight ratio than any of the individual materials used to form the composite. Alternatively, the core may be made of a resin, epoxy or cementitious material. Further, core 110 may be any shape, e.g., flat, round, conical or curved, depending on the shape of sheets 116, 122. Fig. 5 shows a core 110 formed between perforated sheets 116, 122 using a mold 250. The mold may have steel frame portions 254, 256 containing magnets 260, 262. The sheets may be held within mold cavity 252 using, e.g., magnets 260, 262. Back surfaces 120, 126 of sheets 116, 122 are held spaced apart from each other, creating a space within mold cavity 252 in which the core is formed. Sheets 116, 122 are bonded to core 110 by injection molding, casting or laminating. For example, to form file 100, a liquid or semi-solid material, e.g., heated plastic material, that forms core 110 may be forced between sheets 116, 122 under injection pressure. During the injection molding, the liquid or semi-solid material flows into the space to create the core and flows into the perforation holes 128 in sheets 116, 122. For the alternative anchoring members shown in Figs. 10-12, the material may flow around the studs 602 or into the perforations in sheets 620, 622 or the open areas of expanded metal sheet 628. The liquid or semi-solid material hardens, by cooling or curing, to form the core. Core 110 is then anchored to sheets 116, 122, since the core material that has flowed around studs 602 or into perforation holes 128 or open areas of expanded mental sheet 628 resists separation of core 110 from sheets 116, 122, particularly if the perforation holes are counterbored or bevelled as described above. The core may be a solid structure as shown in Fig. 1. Alternatively, the core may have holes or hollowed-out portions. Figs. 13-15 show an alternative embodiment of a file 400 including sheets 116, 122 having long and short edges and a core 405 having hollow spaces 410a...410c. In the embodiment of Figs. 13-15, sheets 116, 122 are held in parallel planes spaced apart by a distance h. Core 405 includes upper wall 312 and lower wall 314, to which sheets 116, 122, respectively, are attached. Core 405 includes a central wall 416 extending between the upper and lower walls, the central wall being perpendicular to the planes of sheets 116, 122 and running along a length 1 of the interior portion of sheets between the long edges of the sheets. Core 405 also includes a series of vertical side walls 420a...420d, 430a...430d extending between the upper and lower walls and disposed perpendicular to central wall 316, each side wall extending from the central wall to one of the long edges of the sheets. In addition, side walls 420a, 420d, 430a, 430d are formed along the short edges of sheets 116, 122 across width w to support the ends of the sheets. This construction results in a core with hollow spaces 410a...410c and a first wall and a second wall that are spaced apart from each other. The core of the embodiment of Figs. 13-15 has a thin-walled construction, which requires less material to form the core and results in a faster molding cycle and reduced internal stresses on the core material. The hollow spaces also provide a resting place for a user's fingers, so that the user's knuckles do not contact the surface to which the abrasive tool is being applied. Moreover, the construction shown in Figs. 13-15 results in greater stiffness over other thin-walled core designs, since the stiffness is proportional to the second power of the distance of the core material to a central neutral surface in the interior of the core, as is the case with "I"-shaped structure beams. The increased stiffness also results in enhanced dimensional stability and flatness of attached sheets 116, 122. Abrasive surfaces 133, 134 are formed on front surfaces 118, 124 of sheets 116, 122. Abrasive surfaces 133, 134 may be, e.g., grinding, honing, lapping or deburring surfaces, and may be, e.g., flat or curved, depending on the shape and use of the abrasive tool. Abrasive surfaces 133, 134 are formed by bonding abrasive grains 136 to front surfaces 118, 124 of sheets 116, 122 in areas other than holes 128. Abrasive grains 136 do not bond to the core material, e.g., plastic, within holes 128. Since abrasive surfaces 133, 134 extend above the surface of sheets 116, 122, front surfaces 118, 124 of sheets 116, 122 have an interrupted cut pattern which provides recesses into which filed or deburred particles or chips may fall while the abrasive tool is being used on a work piece. An abrasive tool with an interrupted cut pattern is able to cut or file the work piece faster by virtue of providing chip clearance. Abrasive grains 136 may be particles of, e.g., superabrasive monocrystalline diamond, polycrystalline diamond, or cubic boron nitride. Abrasive grains 136 may be bonded to front surfaces 118, 124 of sheets 116, 122 by electroless or electrode plated nickel or other plating material or bonding, or by brazing if the core is made of suitably high temperature resistant material. Abrasive surfaces 133, 134 may be given the same degree of abrasiveness by subjecting front surfaces 118, 124 of sheets 116, 122 to identical processes. Alternately, the abrasive surfaces 133, 134 may be given differing degrees of abrasiveness, by bonding different types, sizes, or concentrations of abrasive grains 136 onto the two front surfaces 118, 124 of sheets 116, 122. Abrasive grains 136 may be bonded to front surfaces 118, 124 of sheets 116, 122 by electroplating or anodizing aluminum precharged with diamond. See, e.g., U.S. Patent No. 3,287,862, which is incorporated herein by reference. Electroplating is a common bonding technique for most metals that applies Faraday's law. For example, the sheets 116, 122 bonded to core 110 are attached to a negative voltage source and placed in a suspension containing positively charged nickel ions and diamond particles. As diamond particles fall onto front surfaces 118, 124 of sheets 116, 122, nickel builds up around the particles to hold them in place. Thus, the diamond particles bonded to front surfaces 118, 124 of sheets 116, 122 are partially buried in a layer of nickel. Alternately, abrasive grains 136 such as diamond particles may be sprinkled onto front surfaces 118, 124 of sheets 116, 122, and then a polished steel roller which is harder than sheets 116, 122 may be used to push abrasive grains into front surfaces 118, 124 of sheets 116, 122. For example, in this case sheets 116, 122 may be aluminum. Alternately, abrasive grains 136 may be bonded to front surfaces 118, 124 of sheets 116, 122 by brazing. For example, to bond diamond particles by brazing, a soft, tacky brazing material or shim, e.g., in the form of a paste, spray or thin solid layer, is applied to the front surfaces 118, 124 of sheets 116, 122. The shim is made, e.g., from an alloy of a metal and a flux material that has a melting point lower than the melting point of sheets 116, 122 or core 110. Diamond particles are poured onto the shim, which holds many of the diamond particles in place due to its tackiness. Excess diamond particles that do not adhere to the shim may be poured off. Sheets 116, 122 are then heated until the shim melts. Upon solidification, the diamond particles are embedded in the shim, which is also securely bonded to the front surfaces 118, 124 of sheets 116, 122. In addition, diamond particles can be kept out of the holes 128 in sheets 116, 122 by failing to apply the shim material inside holes 128. Fig. 6 shows a method 1000 for constructing file 100. First, back surfaces 120, 126 of perforated sheets 116, 122 are cleaned (step 1002). In step 1004, sheets 116, 122 are spaced apart from each other. For example, sheets 116, 122 may be retained in a spaced orientation within a mold, with back surfaces 120, 126 facing each other. Core 110 is formed between sheets 116, 122 by injection molding, casting or laminating. With injection molding, liquid or semi-solid core material is injected into the space between sheets 116, 122 and flows into perforation holes 128 (step 1006). The core material then hardens or cures to form the core 110 with sheets 116, 122 bonded thereto (step 1008) . The front surfaces 118, 124 of sheets 116, 122 may be ground or lapped for precision flatness (step 1010). The grinding step also removes any core material that may have flowed though perforation holes 128 and become deposited on one of the front surfaces 118, 124 of the sheets 116, 122. Abrasive grains 136 are then bonded to front surfaces 118, 124 of sheets 116, 122 to form abrasive surfaces 132, 134 (step 1012). In a preferred embodiment, sheets 116, 122 are bonded to core 110 (steps 1006 and 1008) prior to forming abrasive surfaces 132, 134 (step 1012). In particular, the use of a non-conductive plastic core material for core 110 minimizes the quantity of grains 136 that are used; i.e., nickel will not be deposited on non-conductive plastic core 110 during the electroplating process, so that no diamond grains 136 will accumulate on core 110. Alternately, abrasive surfaces may be formed on sheets 116, 122 (step 1012) prior to bonding sheets 116, 122 to core 110 (steps 1006 and 1008). This method of constructing file 100 may be used to construct any abrasive tool structure, including but not limited to the manufacture of a two-sided whetstone. A core formed between two parallel perforated sheets preferably has symmetrical cross sections in planes in three dimensions, i.e., along the length, width and height axes of the core (200, 202 and 204 in Fig. 1). This structure also results in maximum spacing of the sheets from the structurally neutral bending axis. As a result, the distribution and relief of stresses within each plane are symmetrical during subsequent operations with the support structure, e.g., using file 100 for grinding, the net effect being overall dimensional stability of the composite structure. Moreover, a support structure formed by injection molding, casting or laminating the core between two sheets will force shrinking or contracting anisotropically, which helps to control warp or distortion and creates less residual stress on the core. Other embodiments are within the scope of the following claims. In an alternative embodiment, the abrasive tool includes more than two sheets, and thus more than two abrasive surfaces. For example, the use of sheets made of a magnetic material allows for magnetic or vacuum chucking for multiple sharpening surfaces. Such magnetic sheets allow multiple units to be used simultaneously, in the form of a mosaic, such as for a whetstone.

Claims: An abrasive tool, comprising: a first perforated sheet (116) having a front surface and a back surface; a second perforated sheet (122) having a front surface and a back surface; a first layer (133) of abrasive grains (136) bonded to the front surface (118) of the first perforated sheet (116); a second layer (134) of abrasive grains (136) bonded to the front surface (124) of the second perforated sheet (122); and a core (110, 302, 606) made of a first material, the core having a first surface (180) and a second surface (182), the back surface (120, 608) of the first perforated sheet (116) disposed adjacent to the first surface of the core (110) and the back surface (176, 610) of the second perforated sheet (122) disposed adjacent to the second surface (182) of the core (110), the core being bonded to the first perforated sheet (116) and the second perforated sheet (122) by forming the core (110) between the first perforated sheet (116) and the second perforated sheet (122). An abrasive tool as claimed in Claim 1 in which the core is made of a first material, the core (110) including a first wall having an inner surface and an outer surface, a second wall having an inner surface and an outer surface, and a plurality of walls each connected to both the inner surface of the first wall and the inner surface of the second wall to space the first wall from the second wall and to form a plurality of hollow spaces (410) within the core, the back surface of the first perforated sheet (116) being disposed adjacent to the outer surface of the first wall and the back surface of the second perforated sheet (122) being disposed adjacent to the outer surface of the second wall, and the core being bonded to the first perforated sheet (116) and the second perforated sheet (122) by forming the core between the first perforated sheet (116) and the second perforated sheet (122). An abrasive tool as claimed in Claim 2 in which the plurality of walls form the plurality of hollow spaces (410) along an edge of the abrasive tool. An abrasive tool as claimed in any preceding claim in which each portion adjacent to the front surface of the sheet that is wider than a portion of the perforation (128) that is adjacent to the back surface of the sheet. An abrasive tool as claimed in Claim 4 in which the perforations (128) are bevelled (528a). An abrasive tool as claimed in Claim 4 in which the perforations (128) are counterbored (528b,c). An abrasive tool as claimed in any preceding claim in which the first and second perforated sheets (116, 122) have perforations (128) arranged to form an interrupted cut pattern. An abrasive tool as claimed in any one of Claims 1 to 6 in which the first sheet and the second sheet (116, 122) have perforations (128) in a portion less than the entirety of the sheets. An abrasive tool as claimed in any preceding claim in which the core (110) is formed by injection molding. An abrasive tool as claimed in any one of Claims 1 to 8 in which the core (110) is formed by casting. An abrasive tool as claimed in any one of Claims 1 to 8 in which the core (110) is formed by laminating. An abrasive tool as claimed in any preceding claim in which the first material comprises a plastic material. An abrasive tool as claimed in Claim 12 in which the plastic material is a glass filled polycarbonate composite. An abrasive tool as claimed in any one of Claims 1 to 11 in which the first material comprises resin. An abrasive tool as claimed in Claim 14 in which the first material comprises epoxy. An abrasive tool as claimed in any one of Claims 1 to 11 in which the first material comprises a cementitious material. An abrasive tool as claimed in any preceding claim in which the first and second layers (133, 134) of abrasive grains (136) are bonded to the front surfaces of the first and second perforated sheets respectively by a plating material. An abrasive tool as claimed in any preceding claim in which the first and second layers (133, 134) of abrasive grains (136) have different degrees of abrasiveness. An abrasive tool as claimed in any preceding claim in which the tool is a file. An abrasive tool as claimed in any preceding claim in which the tool is a whetstone. A method of assembling an abrasive tool, comprising: providing a first perforated sheet (116) having a front surface and a back surface and perforations (128) therein; providing a second perforated sheet (122) having a front surface and a back surface and perforations (128) therein; orienting the back surfaces of the first and second perforated sheets (116,122) spaced apart from and facing each other; forming a core (110) between the spaced apart back surfaces of the first and second perforated sheets (116,122); bonding a first layer of abrasive grains (133) to the front surface of the first perforated sheet (116), and bonding a second layer of abrasive grains (134) to the front surface of the second perforated sheet (122). A method as claimed in Claim 21 in which the core (110) is formed by injecting a first material between the spaced apart back surfaces of the first and second perforated sheets (116,122) and the first material is hardened. A method as claimed in Claim 22 in which the first material injected between the spaced a part back surfaces of the first and second perforated sheets (116, 122) flows into the perforations in the first and second perforated sheets (116,122). A method as claimed in Claim 21 in which the core (110) is formed by casting. A method as claimed in Claim 21 in which the core (110) is formed by laminating. A method as claimed in Claim 21 or Claim 22 in which the orienting step includes placing the first and second perforated sheets (116,122) into a mold. A method as daimed in any one of Claims 21 to 26 further comprising the step of grinding the front surfaces of the first and second perforated sheets (116,122). A method as daimed in any one of Claims 21 to 27 in which the bonding of the first and second layers of abrasive grains (133,134) to the front surfaces of the first and second perforated sheets (116,122) respectively comprises electroplating. A method as claimed in any one of Claims 21 to 27 in which the bonding of the first and second layers of abrasive grains (133,134) to the front surfaces of the first and second perforated sheet (116,122) respectively comprises anodizing. A method as claimed in any one of Claims 21 to 27 in which the bonding of the first and second layers of abrasive grains (133,134) to the front surfaces of the first and second perforated sheets (116,122) respectively comprises brazing.

Inventors: POWELL DAVID G, WATSON STANLEY A, POWELL, DAVID G., WATSON, STANLEY A.
Applicants: POWELL DAVID G, VOGEL CAPITAL INC, POWELL, DAVID G., VOGEL CAPITAL, INC.
Application year: 1999
Main classification: B24D18
IPC codes: B24D18, B24B23, B24D15, B23D71