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BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to cutters for use on rotary drill bits for drilling subterranean formations and, more specifically, to a cutter including a superabrasive table including a cutting face and a side jacket over a supporting substrate, as well as rotary drill bits carrying such cutters. 
     2. State of the Art 
     Superabrasive materials, normally diamond, have been employed in cutting elements for rotary drill bits for decades. For about the past twenty-five years there has been widespread use of synthetic diamond cutters, specifically in the form of polycrystalline diamond compacts. Polycrystalline diamond compact cutters, commonly known as PDCs, have been commercially available for over 20 years. PDCs may be self-supporting, or may comprise a diamond “table” bonded during formation to a supporting substrate. A diamond table/substrate cutter structure is formed by stacking into a cell layers of fine diamond crystals (100 microns or less) and metal catalyst powder, alternating with wafer-like metal substrates of cemented tungsten carbide or other suitable materials. In some cases, the catalyst material may be incorporated in the substrate in addition to or in lieu of using a powder catalyst intermixed with the diamond crystals. A loaded receptacle is subsequently placed in an ultra-high temperature (typically 1450-1600° C.) ultra-high pressure (typically 50-70 kilobar) diamond press, wherein the diamond crystals, stimulated by the catalytic effect of the metal powder, bond to each other and to the substrate material. The spaces in the diamond table between the diamond to diamond bonds are filled with residual metal catalyst. A so-called thermally stable PDC product (commonly termed as “TSP”) may be formed by leaching out the metal in the diamond table. Alternatively, silicon, which possesses a coefficient of thermal expansion similar to that of diamond, may be used to bond diamond particles to produce a Si-bonded TSP. TSPs are capable of enduring higher temperatures (on the order of 1200° C.) without degradation in comparison to normal PDCs, which experience thermal degradation upon exposure to temperatures of about 750-800° C. 
     While PDC and TSP cutters employed in rotary drag bits for earth boring have achieved major advances in obtainable rate of penetration while drilling and in greatly expanding the types of formations suitable for drilling with diamond bits at economically viable cost, the diamond table/substrate configurations of state of the art cutters, typically employing substantially planar superabrasive tables having a variety of interface configurations with a supporting substrate, leave something to be desired. 
     First, bending, attributable to the loading of the cutting element by the formation, may cause fracture or even delamination of the diamond table from the substrate. It is believed that such degradation of the cutting element is due, at least in part, to lack of sufficient stiffness of the cutting element so that when encountering the formation the diamond table actually flexes due to lack of sufficient rigidity or stiffness. As diamond has an extremely low strain to failure (diamond cannot tolerate large values of absolute strain), only a small amount of flex can initiate fracture. In addition, fracture may also be initiated in the highly stressed carbide substrate when cutting loads are applied to the cutting element, as the carbide is stressed in tension during cooling after the previously-described fabrication process due to the difference in coefficients of thermal expansion between the diamond and the substrate material. 
     A second limitation of PDCs is due to excessive buildup of heat due to frictional forces generated during the cutting process. While the superabrasive material of the cutting element table has an extremely high thermal conductivity (on the order of 400 to over 600 watts/meter Kelvin) and the substrate has a relatively high thermal conductivity (on the order of 100 watts/meter Kelvin), the bit body, typically steel or WC matrix, has a far lower thermal conductivity (on the order of 30 watts/meter Kelvin). As the cutting element wears and the point of contact with the formation becomes an ever-wider wear flat, the cutting element is subjected to higher cutting energies and the substrate becomes ever-smaller, limiting and actually reducing the potential rate of heat transfer. The heat buildup causes overheating of the cutting element and accelerated wear of the diamond table and supporting substrate. In “dull” or used bits, such excessive heating is often manifested on the WC substrate behind the diamond table by the phenomenon of “heat checking”, which comprises vertically running fractures in a checkerboard pattern. 
     It has been proposed to enhance the stiffness of superabrasive cutting elements by providing the superabrasive table with a linearly-extending portion of enhanced thickness. Such a configuration provides additional stiffness for the cutting structure, and also beneficially increases compressive stresses in the superabrasive material table while lowering tensile stresses in the supporting substrate. A number of variations of this approach are described in co-pending U.S. Pat. No. 5,435,403 to Gordon A. Tibbitts, assigned to the assignee of the present invention and incorporated herein by this reference. 
     It has also been proposed to provide superabrasive cutters with diamond tables including one or more struts or other protrusions of superabrasive material extending rearwardly into the substrate to enhance stiffness of the table, as well as, or alternatively, to enhance heat transfer from the cutting edge and cutting face of the diamond table. U.S. Pat. No. 5,590,729 to Cooley et al., assigned to the assignee of the present invention and incorporated herein by this reference, discloses a variety of such cutters. 
     Yet another advance in the art was the recognition that cutters in different locations on drill bits experience loading of different magnitudes and types during a drilling operation, and that cutters might be designed and selected to best accommodate loading at the different locations. U.S. Pat. No. 5,605,198 to Tibbitts et al., assigned to the assignee of the present invention and incorporated herein by this reference, discloses such design and selective placement of cutters. 
     U.S. Pat. No. 5,590,727 to Tank discloses several cutter configurations employing a stepped interface between superabrasive material and a supporting substrate, the superabrasive material extending down an exterior side of the cutter. 
     U.S. Pat. No. 5,667,028 to Truax et al. discloses a variety of cutter configurations employing so-called “secondary” PDC cutting surfaces placed on the side of the substrate in spaced relationship to the PDC diamond table, the secondary cutting surfaces purportedly reducing the rate of erosion of the substrate material during drilling. 
     However, despite the above-referenced developments, significant shortcomings are still exhibited by conventional cutters in certain situations. For example, erosion or abrasion of the cutter substrate immediately to the rear of the superabrasive table results in the beneficial formation of a protruding “lip” of superabrasive material and conventional thought is to the effect that the presence of such a lip facilitates the cutting action of the cutter. However, the inventors herein have recognized that the well-known phenomenon of so-called bit “whirl”, wherein a bit rotates or precesses in the borehole counter to the direction of bit rotation by the drill string or downhole motor, may result in the superabrasive lip “catching” on the uncut formation of the borehole bottom or wall so that the superabrasive table is placed in tension, precipitating delamination of the table from the substrate. Further, the inventors have recognized that in more ductile, elastic formations, subsequent to shearing of formation material by the superabrasive table of a cutter, the still-uncut formation adjacent the cutter rebounds and contacts the substrate to the rear of the table. This phenomenon, occurring on a continuing basis as the bit rotates, results in the aforementioned heat checking of the substrate and attendant breakdown in physical support for the superabrasive table. 
     Accordingly, there remains a significant need in the art for improvements in cutter integrity, impact resistance and heat transfer capabilities. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention includes a cutter comprising a superabrasive volume including a cutting face portion extending transversely across at least a portion of a leading end of a supporting substrate and a contiguous jacket portion extending rearwardly over the supporting substrate along a portion of its side periphery comprising a surface of revolution. Interfaces between the respective superabrasive volume cutting face and jacket portions and adjacent exterior surfaces of the supporting substrate are each irregular. More specifically, the leading face of the substrate may include one or more grooves extending toward the jacket at least partially across the leading face from the side of the substrate opposite the jacket, the superabrasive material extending into the grooves. Similarly, the side periphery of the substrate defining the location of the jacket may be grooved at one or more adjacent locations with substantially axially-oriented grooves extending rearwardly from the leading end of the substrate to a position closer to the trailing end of the substrate. Substantially axially-oriented ridges intermediate the side periphery grooves may not extend radially outwardly to a full radius of the adjacent substrate portion so that the superabrasive material of the jacket extends not only into the circumferential grooves but also circumferentially therebetween, providing a continuous, arcuate superabrasive surface having substantially the same exterior radius as that of the substrate portion adjacent the jacket. Alternatively, if the ridges extend to the full radius of the substrate portion adjacent the jacket, the jacket may comprise mutually adjacent but separate ribs of superabrasive material rather than a continuous surface. 
     The asymmetrical design of the inventive cutter provides a significant substrate surface area for brazing of the cutters into pockets on the face of a bit while protecting the carbide material of the cutter substrate on the bottom side of the cutter (as the cutter is normally oriented on the bit), as well as the interface between the superabrasive table and the substrate. 
     Rotary drill bits for subterranean drilling bearing cutters according to the present invention are also included within the scope of the invention. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 is a perspective view, inverted from a normal drilling position, of a rotary drag bit bearing cutters according to the present invention; 
     FIG. 2 is a first perspective view of a substrate of a first embodiment of a cutter according to the present invention; 
     FIG. 3 is a second perspective view of the substrate of FIG. 2; 
     FIG. 4 is a frontal elevation of the substrate of FIG. 2; 
     FIG. 5 is a side elevation of the first embodiment of a cutter of the present invention; 
     FIG. 6 is a perspective view of a substrate of a second embodiment of a cutter of the present invention; 
     FIG. 7 is a frontal elevation of the substrate of FIG. 6; 
     FIG. 8 is a bottom elevation (looking at the cutter from the perspective of the formation being cut) of the second and third embodiments of a cutter of the present invention; 
     FIG. 9 is a perspective view of an exemplary cutter according to the invention after substantial wear during drilling; 
     FIG. 10 is a perspective view of a substrate of a third embodiment of a cutter of the present invention as viewed from the front and the side normally adjacent a formation being drilled; 
     FIG. 11 is a frontal elevation of the substrate of FIG. 10; and 
     FIG. 12 is a perspective view of the substrate of FIG. 10 as viewed from the side normally secured to a bit face. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG. 1 of the drawings, an exemplary rotary drag bit  200  is depicted. Bit  200  includes a bit body  202  having a face  204 , above which extends a plurality of blades  206 . Fluid courses  208  on the face  204  extend radially outwardly between blades  206  and communicate with junk slots  210  located between gage pads  212 , which in this instance comprise longitudinal extensions of blades  206 . Nozzles  214  located in apertures  216  in bit face  204  provide drilling fluid flow to remove formation cuttings from the bit face and cool and clean the superabrasive cutters  218  on blades  206 . Smaller diameter superabrasive cutters  220  act as gage trimmers to maintain the borehole gage drilled by the bit  200 . As shown, cutters  218  and  220  are brazed or otherwise secured in pockets  222  formed on the blades during fabrication of bit  200 . Bit shank  224  includes a threaded pin connection  226  thereon for securing bit  200  to a drill string or a downhole motor at the end of a drill string, as known in the art. A central bore (not shown) leading through bit shank  224  introduces drilling fluid received from the drill string or motor into a plenum or discrete passages extending to apertures  216  in bit face  204 , again as known in the art. At least some of superabrasive cutters  218  and  220  comprise cutters according to the present invention as will be hereinafter described with respect to FIGS. 2-12 of the drawings. As noted above, bit  200  is exemplary only and is in no way limiting as to the design or style of bit on which the cutters according to the present invention may be placed. 
     Referring now to FIGS. 2 through 5 of the drawings, features of a first cutter embodiment  10  according to the present invention comprise a superabrasive volume  12  formed onto a supporting substrate  14  according to ultra-high temperature, ultra-high pressure techniques referenced above and well known in the art. The superabrasive volume preferably comprises a PDC, although it may optionally comprise a TSP or a cubic boron nitride compact. The supporting substrate preferably comprises a cemented tungsten carbide structure, preformed and placed in a diamond press with diamond crystals and a catalyst. Superabrasive processes being well known in the art, no further description thereof is necessary. 
     Superabrasive volume  12  (see FIG. 5) comprises a cutting face  16  extending in two dimensions substantially transverse to longitudinal axis L of cutter  10  and having a cutting edge  18  at a lateral periphery thereof. Superabrasive volume  12  also includes a contiguous jacket  20  extending rearwardly from cutting edge  18  over the side of substrate  14 . 
     Substrate  14 , as shown, (see particularly FIGS. 2-4) is substantially cylindrical and includes a leading end  22 , a trailing end  24 , and a side periphery  26 . A portion  28  of the side periphery  26  comprises a surface of revolution, while another portion  30  lies inset from the surface of revolution and defines the location of superabrasive jacket  20  on the side periphery  26  of substrate  14 . 
     Leading end  22  of substrate  14  comprises an irregular surface including a plurality of mutually parallel grooves  32  in substantially planar surface  34  extending from side periphery  26  from a location substantially opposed to portion  30  of side periphery  26  of substrate  14 , and toward portion  30 . Grooves  32  preferably include concave bottoms  36  and convex, radiused side borders  38  transitioning from substantially planar surface  34  to concave bottoms  36  of substantially constant radius. Grooves  32  may terminate by tapering arcuately into substantially flat ends  40 , into which side borders  38  also taper. Alternatively, as shown in broken lines  42 , grooves  32  may extend completely across leading end  22 . 
     Portion  30  of the side periphery  26  comprises a plurality of axially-extending, circumferentially spaced grooves  50 , between which lie axially-oriented ridges  52  of substantially constant radius with respect to axis L, the radially outer surfaces  54  of which terminate short of the surface of revolution defined by portion  28  of the side periphery  26 . Convex, radiused end borders  56  lead from substantially planar surface  34  of leading end  22  to leading edges of concave bottoms  58  of grooves  50  and leading edges of ridges  52 . If, as noted above, leading end grooves  32  extend across leading end  22  to intersect some or all of side periphery grooves  50 , the intersections  60  of the mutually perpendicular grooves  32  and  50  may be similarly radiused. The borders  62  between ridges  52  and side groove bottoms  58  are also convex and radiused, as are the borders  64  respectively between grooves  50  and ridges  52  and semi-annular floor  66 , which lies near trailing end  24  of substrate  14  and is substantially transverse to longitudinal axis L. 
     As best shown in FIG. 5, cutting face  16  of superabrasive volume  12  may comprise a substantially planar leading surface  70  extending at least partially across leading end  22  of substrate  14 , and may include a peripheral chamfer  72  at least adjacent cutting edge  18 . As used herein, the term “substantially planar” includes not only flat leading surfaces but those of concave, convex, grooved, stepped, ridged and other configurations which nonetheless extend in two dimensions substantially transverse to longitudinal cutter axis L. Jacket  20  preferably includes a convex exterior surface  74  of substantially the same radius as that of portion  30  of side periphery  26  and coaxial therewith so that the substrate  14  and overlying jacket  20  define a single surface of revolution. Exemplary interior details of some of the grooves  32  and  50  in substrate  14  are shown in FIG. 5 for clarity. 
     It should be noted that the material of superabrasive volume  12  extends into both grooves  32  and  50 , defining ribs  90  and  92 , which in substantial part provide the aforementioned irregular interfaces between the superabrasive volume  12  and substrate  14 . The above-noted radially foreshortened nature of the ridges  52  provides a continuous shell  94  of superabrasive material over ribs  92 , while cutting face  16  extends in a continuous manner over ribs  90 . Alternatively, although not currently preferred for all drilling applications, ridges  52  may extend to the full radius of cutter  10  so that ribs  92  are exposed on the side surface of the substrate  14 . 
     As shown in FIG. 5, cutter  10  is located in a pocket  222  on a blade  206  of a bit  200 , such as is shown in FIG. 1, so that superabrasive jacket  20  faces generally away from bit face  204  and the cemented tungsten carbide of substrate  14  on the inwardly-facing portion of side periphery  26  as well as on the trailing end  24  of substrate  14  are exposed for brazing cutter  10  as shown at  96  into pocket  222 . 
     Also, as shown in FIG. 5, it is notable that cutter  10  may be configured as a so-called “stud” cutter employing a transverse substrate projection  114  shown in broken lines which is receivable in a socket in a face or blade of a steel-bodied bit. With such a substrate configuration, it will be appreciated that only a portion of substrate  14  will be cylindrical, so that the side periphery  26  thereof comprises only a partial surface of revolution. It is also contemplated that the substrate  14  may be entirely or partially of a frustoconical configuration, presenting at least a partially tapered surface of revolution side periphery, as disclosed in the context of a taper of increasing radius behind the cutting face in U.S. Pat. No. 5,460,233 to Meany et al. and in the context of a decreasing radius taper in U.S. Pat. No. 5,377,773 to Tibbitts, each of these patents assigned to the assignee of the present invention and each incorporated herein by this reference. 
     Referring now to FIGS. 6-8 of the drawings, features of a second cutter embodiment  100  according to the present invention are depicted. For clarity, features of second cutter embodiment  100  already identified with respect to first cutter embodiment  10  will be identified by like reference numerals. 
     Second cutter embodiment  100 , according to the present invention, comprises a superabrasive volume  12  formed onto a supporting substrate  14  according to the aforementioned ultra-high temperature, ultra-high pressure techniques. The superabrasive volume  12  again preferably comprises a PDC, although it may optionally comprise a TSP or a cubic boron nitride compact. The supporting substrate  14  preferably comprises a cemented tungsten carbide structure, preformed and placed in a diamond press with diamond crystals and a catalyst. 
     Superabrasive volume  12  comprises a cutting face  16  extending in two dimensions substantially transverse to longitudinal axis L of cutter  100  and having a cutting edge  18  at a lateral periphery thereof. Superabrasive volume  12  also includes a contiguous jacket  20  extending rearwardly from cutting edge  18  over the side of substrate  14 . 
     Substrate  14  is substantially cylindrical and includes a leading end  22 , a trailing end  24 , and a side periphery  26 . A portion  28  of the side periphery  26  comprises a surface of revolution, while another portion  30  lies inset from the surface of revolution and defines the location of superabrasive jacket  20  on the side periphery  26  of substrate  14 . 
     Leading end  22  of substrate  14  comprises an irregular surface including a plurality of mutually parallel grooves  32  in substantially planar surface  34  extending from side periphery  26  at a location substantially opposed to portion  30  of side perphery  26  of substrate  14 , and toward jacket  20 . Grooves  32  preferably include concave bottoms  36  and convex, radiused side borders  38  transitioning from substantially planar surface  34  to concave bottoms  36 . Grooves  32  terminate in quarter-spherical concave ends  140  of substantially the same radius as concave bottoms  36 , side borders  38  extending into concave end borders  138  of like radius between concave ends  140  and substantially planar surface  34 . Alternatively, as noted with respect to cutter  10 , grooves  32  may extend completely across leading end  22 . 
     Portion  30  of the side periphery  26  comprises a plurality of axially-extending, circumferentially spaced grooves  150 , between which lie axially-oriented ridges  152  of increasing radius with respect to axis L and of increasing cross-sectional area as ridges  152  extend away from leading end  22 . The radially outer surfaces  154  of ridges  152  terminate short of the surface of revolution defined by portion  28  of the side periphery  26 . Convex, radiused end borders  56  lead from substantially planar surface  34  of leading end  22  to leading edges of concave bottoms  158  of grooves  150  and leading edges of ridges  152 . Unlike the bottoms  58  of grooves  50  of cutter  10 , bottoms  158  of grooves  150  of cutter  100  are of decreasing radius as grooves  150  extend away from leading end  22 . If, as noted above, leading end grooves  32  extend across leading end  22  to intersect some or all of side periphery grooves  150 , the intersections of the mutually perpendicular grooves  32  and  150  may also be radiused. The borders  162  between ridges  152  and side groove bottoms  158  are also convex and radiused, as are the borders  164  respectively between grooves  150  and ridges  152  and semi-annular floor  166 , which lies near trailing end  24  of substrate  14  and is substantially transverse to longitudinal axis L. 
     As best shown in FIG. 8, cutting face  16  of superabrasive volume  12  of cutter  100  may comprise a substantially planar leading surface  70  extending at least partially across leading end  22  of substrate  14 , and may include a peripheral chamfer  72  at least adjacent cutting edge  18 . As used herein, the term “substantially planar” includes not only flat leading surfaces but those of concave, convex, grooved, stepped, ridged and other configurations which nonetheless extend in two dimensions substantially transverse to longitudinal cutter axis L. Jacket  20  preferably includes a convex exterior surface  74  of substantially the same radius as that of portion  28  of side periphery  26  and coaxial therewith so that the substrate  14  and overlying jacket  20  define a substantially continuous surface of revolution. Due to the configuration of the side boundaries of portion  30  of side periphery  26  of substrate  14  of cutter  100 , it should be noted that jacket  20  may taper to a slightly smaller width transverse to axis L as it extends away from the leading end of cutter  100 . 
     It should be noted that, as with cutter  10 , the material of superabrasive volume  12  of cutter  100  extends into both grooves  32  and  150 , defining ribs which in substantial part provide the aforementioned irregular interfaces between the superabrasive volume  12  and substrate  14 . The above-noted radially foreshortened nature of the ridges  152  provides a continuous shell of superabrasive material over the leading end ribs, while cutting face  16  extends in a continuous manner over the side ribs. Alternatively, although not currently preferred for all drilling applications, the ridges  152  may extend to the full radius of the cutter  100  so that the superabrasive material in grooves  150  comprises exposed longitudinally extending ribs. 
     As with cutter  10 , cutter  100  may be mounted in a pocket on the face of a bit such as is shown in FIG. 1 so that superabrasive jacket  20  faces generally away from the bit face and the cemented tungsten carbide of substrate  14  on the inwardly-facing portion of side periphery  26 , as well as on the trailing end  24  of substrate  14  are exposed for brazing cutter  10  into a pocket. Also, as with cutter  10 , cutter  100  may be configured as a stud cutter, may employ a substrate having at least a portion of frustoconical configuration, or both, as desired. 
     Referring now to FIGS.  8  and  10 - 12  of the drawings, features of a third cutter embodiment  300  according to the present invention are depicted. For clarity, features of third cutter embodiment  300  already identified with respect to first and second cutter embodiments  10  and  100  will be identified by like reference numerals. 
     Third cutter embodiment  300  according to the present invention comprises a superabrasive volume  12  formed onto a supporting substrate  14  according to the aforementioned ultra-high temperature, ultra-high pressure techniques. The superabrasive volume  12  again preferably comprises a PDC, although it may optionally comprise a TSP or a cubic boron nitride compact. The supporting substrate  14  preferably comprises a cemented tungsten carbide structure, preformed and placed in a diamond press with diamond crystals and a catalyst. 
     The superabrasive volume  12 , as with volumes  12  of cutters  10  and  100 , comprises a cutting face  16  extending in two dimensions substantially transverse to longitudinal axis L of cutter  300  and having a cutting edge  18  at a lateral periphery thereof. The superabrasive volume  12  also includes a contiguous jacket  20  extending rearwardly from the cutting edge  18  over the side of substrate  14 . FIG. 8 is a representation of the exterior appearance of cutter  300  as well as of cutter  100 , and the superabrasive volume and its features on cutter  300  need not be further described at this juncture. 
     Substrate  14  is substantially cylindrical and includes a leading end  22 , a trailing end  24 , and a side periphery  26 . A portion  28  of the side periphery  26  comprises a surface of revolution, while another portion  30  lies inset from the surface of revolution and defines the location of superabrasive jacket  20  on the side periphery  26  of substrate  14 . 
     Leading end  22  of substrate  14  comprises an irregular surface including a plurality of mutually parallel grooves  32  in substantially planar surface  34  extending from side periphery  26  of substrate  14  at a location substantially opposed to portion  30  of side periphery  26 , and toward jacket  20 . Grooves  32  preferably include concave bottoms  36 . Grooves  32  terminate in arcuate, concave ends  340  proximate the intersection of leading end  22  and portion  30  of side periphery  26 , thus extending substantially across leading end  22 . 
     The intersection  342  between leading end  22  and portion  30  of substrate  14  is substantially straight, transverse to longitudinal axis L and is substantially rounded or radiused. Portion  30  of the side periphery  26  comprises a plurality of substantially axially-extending, laterally-spaced side periphery grooves  350  in the surface of, and longitudinally shorter than, flat  330 , which may be parallel to longitudinal axis L or inclined at a slight angle thereto. Grooves  350  may be, as shown, more tilted or inclined toward longitudinal axis L than flat  330  so as to be deeper at their leading ends. The trailing end  332  of flat  330  curves outwardly to the radius of portion  28  of side periphery  26  of substrate  14 . Axially-oriented ridge  352  of substantially constant width lies between grooves  350 . The radially outer surface  354  of ridge  352  is substantially coplanar with flat  330  and terminates short of the surface of revolution defined by portion  28  of the side periphery  26 . As illustrated, grooves  350  lie between leading end grooves  32 . If, as noted above with respect to cutters  10  and  100 , leading end grooves  32  extend across leading end  22  to intersect some or all of side periphery grooves  350 , the intersections of the substantially mutually transverse grooves  32  and  350  may also be radiused. 
     Again referring to FIG. 8, cutting face  16  of superabrasive volume  12  may comprise a substantially planar leading surface  70  extending at least partially across leading end  22  of substrate  14 , and may include a peripheral chamfer  72  at least adjacent cutting edge  18 . As used herein, the term “substantially planar” includes not only flat leading surfaces but those of concave, convex, grooved, stepped, ridged and other configurations which nonetheless extend in two dimensions substantially transverse to longitudinal cutter axis L. Jacket  20  preferably includes a convex exterior surface  74  of substantially the same radius as that of portion  28  of side periphery  26  and coaxial therewith so that the substrate  14  and overlying jacket  20  define a substantially continuous surface of revolution. Due to the configuration of the side boundaries of portion  30  of side periphery  26  of substrate  14  of cutter  300 , it should be noted that jacket  20  may taper to a slightly smaller width transverse to axis L as it extends away from the leading end of cutter  300 . 
     It should be noted that, as with cutters  10  and  100 , the material of superabrasive volume  12  of cutter  300  extends into both grooves  32  and  350 , defining ribs which in substantial part provide the aforementioned irregular interfaces between the superabrasive volume  12  and substrate  14 . The above-noted radially foreshortened nature of ridge  352  provides a continuous shell of superabrasive material over the side ribs, while cutting face  16  extends in a continuous manner over the leading end ribs. Alternatively, although not currently preferred for all drilling applications, ridge  352  may extend to the radius of portion  28  of side periphery  26  and flat  330  may be eliminated so that a jacket  20  comprising adjacent ribs of superabrasive material, rather than a continuous jacket  20 , is exhibited on the side periphery  26  of the cutter  300 . 
     As with cutters  10  and  100 , cutter  300  may be mounted in a pocket on the face of a bit such as is shown in FIG. 1 so that superabrasive jacket  20  faces generally away from the bit face and the cemented tungsten carbide of substrate  14  on the inwardly-facing portion of side periphery  26  as well as on the trailing end  24  of substrate  14  is exposed for brazing cutter  10  into a pocket. Also, as with cutters  10  and  100 , cutter  300  may be configured as a stud cutter, may employ a substrate having at least a portion of frustoconical configuration, or both, as desired. 
     The invention as disclosed herein provides several notable advantages over state of the art cutters. First, the complex geometry of the superabrasive volume  12 , with its cutting face  16  and contiguous jacket  20 , results in beneficial compressive loading of the superabrasive material, whether normal loading attributable to weight on bit or tangential loading attributable to bit rotation predominates on the cutter. This advantage is particularly significant in the context of precluding formation of a continuous superabrasive lip transverse to the longitudinal axis of the cutter and along the cutting edge of the superabrasive table, which lip might be susceptible to catching on the formation and initiating delamination of the superabrasive table, as described above. Further, the irregular interfaces between the superabrasive volume  12  and the supporting substrate  14  lower residual tensile stresses (induced by the fabrication process) within the cutter at and adjacent the interfaces and isolate any regions of residual tensile stress so as to minimize the potential for cumulative stresses to cause cutter degradation and failure under loading. The ribs of superabrasive material extending into the substrate along the interfaces also provide additional superabrasive material volume to facilitate heat transfer from the superabrasive cutting face  16  and jacket  20 , thus maintaining the superabrasive material in those regions at a lower temperature and reducing the potential for premature, heat-induced degradation of those regions as well as in the underlying substrate material. Use of a superabrasive jacket  20  contiguous with the cutting face  16  and located on the side periphery  26  of a cutter  10 ,  100  makes the cutter  10 ,  100  very wear-resistant in abrasive sands and affords protection to the carbide material of the substrate to substantially reduce the possibility of substrate heat-checking in limestones and other more ductile or elastic formations such as tougher mudstones or shales. Thus, physical support for the superabrasive table is maintained. Moreover, if the jacket  20  wears through (see FIG. 9) to a depth exposing the superabrasive ribs ( 90 ,  92  shown) respectively extending into the substrate grooves ( 32 ,  50  shown) and the surrounding superabrasive material of the still unworn portion  20   u  of jacket  20 , the mix of superabrasive and substrate material provides an aggressive cutting action. 
     While the present invention has been described with respect to certain preferred embodiments, those of ordinary skill in the art will recognize and appreciate that it is not so limited. Additions or modification to, as well as deletions from, these embodiments may be made without departing from the scope of the invention as defined by the claims which follow. Features from one embodiment may likewise be combined with features from another embodiment. For example, the grooves may be of various configurations other than those disclosed, such as rectangular or substantially cylindrical, the ridges may likewise exhibit other geometries, and the superabrasive jacket may be more tapered, may exhibit other shapes such as half-circular or half-ellipsoidal, or may extend to the trailing end of the substrate. The cutting face may not extend across the entire leading end of the substrate. The cutter may be configured as a half-cylinder, or be formed in a tombstone or other desired shape.

Summary:
A cutter comprising a superabrasive volume including a cutting face portion extending transversely across a leading face of a supporting substrate and a contiguous jacket portion extending rearwardly over the supporting substrate along a portion of its side periphery. Interfaces between the respective superabrasive volume cutting face and cap portions and adjoining surfaces of the supporting substrate are each irregular. The leading face of the substrate includes grooves extending toward the jacket at least partially across the leading face from the side of the substrate opposite the jacket. The side periphery of the substrate defining the location of the jacket is grooved at a plurality of laterally-adjacent locations with substantially axially-oriented grooves extending rearwardly from the leading face of the substrate to a position closer to the trailing face of the substrate. At least one ridge intermediate the side grooves may not extend radially outwardly to a full diameter of the substrate so that the superabrasive material of the jacket extends not only into the circumferential grooves but also circumferentially therebetween, providing a continuous, arcuate superabrasive surface which may have substantially the same exterior diameter as that of the substrate itself. Rotary drill bits for subterranean drilling bearing cutters according to the present invention are also disclosed.