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BACKGROUND OF THE INVENTION 
     This invention relates to an abrasive body and more particularly to an abrasive body which can be used as a tool insert. 
     Composite abrasive compacts are products used extensively as inserts for abrasive tools such as drill bits. Such composite abrasive compacts comprise an abrasive compact layer bonded to a cemented carbide support. The abrasive compact will typically be a diamond abrasive compact, also known as polycrystalline diamond or PCD, or a cubic boron nitride compact, also known as polycrystalline CBN or PCBN. 
     Composite abrasive compacts are manufactured under elevated temperature and pressure conditions, e.g. diamond or cubic boron nitride synthesis conditions. 
     As it is known that PCD composite compacts contain considerable residual stresses as a result of the high temperature/high pressure conditions used in their manufacture. Further, methods of mounting such compacts into drill bits, for example press fitting or brazing, can modify the stress distributions in the compacts. Additional stresses are imposed on the compacts during their use in applications such as drilling. Stresses may be introduced into the interface between the abrasive compact layer and the cemented carbide support. These stresses may be reduced or modified by providing a recess which extends into the cemented carbide support from the compact/carbide interface and which is filled with the abrasive compact. In the prior art, the recess has taken various shapes such as a plurality of concentric rings, a V-shaped recess, a cross-shaped recess, and a recess which incorporates a number of steps. A purpose in most of such designs is to reinforce and support the cutting edge by providing overall rigidity for the composite compacts. 
     U.S. Pat. No. 5,472,376 describes a tool component comprising an abrasive compact layer bonded to a cemented carbide substrate along an interface. A recess extends from the interface into the substrate and is filled with abrasive compact. The recess has a stepped configuration and is located entirely within the carbide substrate. 
     EP 356097 describes a tool insert comprising an abrasive compact bonded to a cemented carbide substrate. The abrasive compact is located in a recess formed in the substrate. The abrasive compact has a top surface which provides a cutting edge for the tool insert, a bottom surface complimentary to the base of the recess and a side surface at least partially located in the recess, the portion of the side surface located in the recess being complimentary to the side of the recess. The side surfaces may be sloping. 
     SUMMARY OF THE INVENTION 
     According to the present invention, an abrasive body, for use, for example, as a tool insert, comprises an abrasive layer bonded to a substrate along an interface and at least one abrasive projection extending from the interface into the substrate, the projection having an essentially elliptical or circular form in plan and a profile which includes a substantially flat central portion and surfaces to either side thereof which slope towards the interface. 
     The projection may lie wholly within the outer surface of the body or may have a portion or section coincident therewith. Two or more such projections may be provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of a first embodiment of the invention, 
     FIG. 2 is a section along the line  2 — 2  of FIG. 1, 
     FIG. 3 is a section along the line  3 — 3  of FIG. 1, 
     FIG. 4 is a sectional side view of a second embodiment of the invention, 
     FIG. 5 is a plan view of a further embodiment of the invention, 
     FIG. 6 is a section along the line  6 — 6  of FIG. 5, 
     FIG. 7 is a section along the line  7 — 7  of FIG.  5 , 
    
    
     DESCRIPTION OF EMBODIMENTS 
     The abrasive body may have various shapes, but is preferably right circular cylindrical. 
     The substrate layer will typically be a cemented carbide substrate layer. The cemented carbide of the substrate may be any known in the art such as cemented titanium carbide, cemented tungsten carbide, cemented tantalum carbide, cemented molybdenum carbide, or mixtures thereof. As is known, such cemented carbides will typically have a binder content of 3 to 30% by mass. The metal binder will typically be cobalt, iron or nickel or an alloy containing one or more of these metals. 
     The abrasive layer will generally be an abrasive compact layer or a layer of diamond produced by chemical vapour deposition (CVD). When the abrasive layer is an abrasive compact layer, it will preferably be a diamond compact layer or a cubic boron nitride compact layer. 
     An embodiment of the invention will now be described with reference to FIGS. 1 to  3 . Referring to these figures, an abrasive body comprises a layer of abrasive compact  40  bonded to a substrate  42 , particularly a cemented carbide substrate, along an interface  44 . The surface  46  of the abrasive compact layer  40  provides an abrasive surface for the body, while the peripheral edge  48  provides a cutting edge, remote from the interface. 
     An abrasive compact projection  50  extends from the interface  44  into the substrate  42 . This projection has essentially an elliptical shape in plan, as can be seen from FIG.  1 . Further, an edge surface  52  is coincident with a side surface of the abrasive body. In use, the peripheral edge  48  of this region of coincidence will be used as the cutting edge. 
     The profile of the projection is illustrated from different directions by FIGS. 2 and 3. It will be noted from these figures that the profile is such that there is a central flat section  56  and surfaces  58  which slope from this central section  56  to the interface  44 . 
     A further embodiment of the invention will now be described with reference to FIGS. 5 to  7 . Referring to these figures, an abrasive body comprises a layer of abrasive compact  80  bonded to a substrate  82 , particularly a cemented carbide substrate, along an interface  84 . The surface  86  of the abrasive compact layer  80  provides an abrasive surface for the body, while the peripheral edge  88  provides a cutting edge, remote from the interface  84 . 
     Two abrasive compact projections  90  extend from the interface  84  into the substrate  82 . The projections are each elliptical in shape, in plan, as can be seen from FIG.  5 . Both projections lie wholly within the outer surface  92  of the abrasive body. Each projection has an elliptical flat base  94  and sides  96  which slope to the interface  84 . 
     The abrasive bodies described above may be made by methods known in the art. Generally, this will involve providing a cylindrical shaped cemented carbide body having a recess, to receive the components necessary to make an abrasive compact, formed in one end thereof. An example of such a body, to produce an abrasive body of FIGS. 1 to  3 , is shown in FIG.  4 . Referring to this figure, a cemented carbide body  60  is of right-circular cylindrical shape having flat ends  62  and  64 . A recess  66  is provided in the end  62 . This recess is filled with the components necessary to make an abrasive compact. The thus produced unbonded assembly is placed in the reaction zone of a conventional high temperature/high pressure apparatus to form an abrasive compact of the components which bonds to the body  60 . The abrasive body illustrated by FIGS. 1 to  3  is produced by simply removing the sides of the body  60 , as illustrated by the dotted lines. However, the bonded body which is recovered from the reaction zone after compact formation and without removal of the carbide sides, may be used as a tool insert itself, and forms another aspect of the invention. In this form of the insert, the edge  70  will provide the cutting edge. This edge is likely to wear away fairly rapidly until the abrasive compact edge  72  is reached. Thereafter it is this edge  72  which provides the cutting edge for the component. 
     The provision of the projections in the abrasive bodies of the invention result in an effective reinforcement and support for the cutting edge by providing overall rigidity for the bodies. Further, in use the cutting edges in the regions of the surfaces  52  of the projection for the FIGS. 1 to  3  embodiment and in the region  98  for the FIGS. 5 to  7  embodiment will generally be employed. The extra abrasive available in these regions increases effectiveness of the abrasive action of the body.

Summary:
An abrasive body which includes an abrasive layer bonded to a substrate along an interface and at least one projection extending from the interface into the substrate. The a projection has an essentially elliptical or circular form in plan and a profile which includes a substantially flat central portion and connecting surfaces joining the central portion to the interface and which slope towards the interface.