Patent Publication Number: US-8528667-B2

Title: Wear resistant material at the leading edge of the leg for a rotary cone drill bit

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a continuation-in-part application from co-pending U.S. application patent Ser. No. 12/896,406 filed Oct. 1, 2010 entitled “Wear Resistant Material at the Shirttail Edge and Leading Edge of a Rotary Cone Drill Bit”, the disclosure of which is hereby incorporated by reference to the maximum extent allowable by law. 
    
    
     BACKGROUND 
     1. Technical Field of the Invention 
     The present invention relates to earth boring bits, and more particularly to those having rotatable cutters, also known as rotary cone drill bits. 
     2. Description of Related Art 
     Reference is made to  FIGS. 1 and 2 , wherein  FIG. 1  illustrates an isometric view of a prior art rotary cone drill bit  10  and  FIG. 2  illustrates a cross-sectional view of a portion of the prior art rotary cone drill bit  10  of  FIG. 1 . A leg  12  depends from a body portion  14  of the drill bit  10 . The leg  12  includes a bearing shaft  16  which extends in a downward and radial inward direction. The bearing shaft  16  includes a cylindrical bearing surface  18 . A cutter cone  20  is mounted to the bearing shaft  16  and supported for rotation by the bearing surface  18 . In an alternative implementation, the cutter cone  20  is supported for rotation on the bearing shaft  16  by a set of roller bearings. The shape and configuration of the cone  20 , as well its rotatable attachment to the bearing shaft  16 , is well known in the art. In sealed bearing implementations, the bearing (journal or roller) between the cone  20  and bearing shaft  16  is lubricated by a lubricant (such as a grease) that fills regions adjacent to the bearing as well as other passages  21  in the rotary cone drill bit in a manner well known by those skilled in the art. This lubricant is retained within the rotary cone drill bit through the use of, for example, a resilient seal in the form of an o-ring  22  positioned in a seal gland  24  between the inner cylindrical surface  26  near the base of the cone  20  and the outer cylindrical surface  28  near the base of the bearing shaft  16 . The lubrication system further includes a pressure compensation assembly  27  installed within an opening  29  formed in an upper shoulder surface  25  of the leg  12 . The opening  29  is coupled to the passage  21 .  FIGS. 1 and 2  illustrate an implementation wherein the opening  29  is formed exclusively in the shoulder surface  25 . It will be understood, however, that the opening  29  may be formed partially in the shoulder surface  25  and partially in the outer (gage or shirttail) surface  30  of the leg  12  (below shoulder surface  25 ). Still further, the opening  29  may be formed in the outer surface  30  of the leg. 
     The outer surface  30  of the leg  12  terminates at a semicircular edge  32  proximal to the cone  20 . The region of the leg  12  associated with the surface  30  is known in the art as the “shirttail region,” and the edge  32  is known in the art as the “shirttail edge.” The shirttail edge  32  is provided where the terminal portion of the outer gage or shirttail surface  30  transitions to an inside radial surface  34  oriented parallel to the base of the cone  20  (and perpendicular to the bearing shaft  16 ) and positioned at the base of the bearing shaft  16 . 
     The outer surface  30  of the leg  12  (below shoulder surface  25 ) in the shirttail region laterally terminates at a leading shirttail edge  50  and a trailing shirttail edge  52 . The leading shirttail edge  50  is especially susceptible to wear during operation of the rotary cone drill bit  10 . The prior art teaches two methods for delaying wear of the leading shirttail edge  50 .  FIG. 3  illustrates a first method in which a layer of welded hardfacing material  40  is applied to the surface  30  extending along at least a portion of the leading shirttail edge  50 . The hardfacing material is typically a deposit of tungsten carbide hardmetal  40 . The material is typically pelletized tungsten carbide carried in a nickel welding medium. This solution does not work well when the rotary cone drill bit is run in a highly abrasive rock formation because the hardfacing material  40  wears down too quickly. It is primarily the welding medium, typically nickel, which accounts for the relative poor performance of the weld on material.  FIG. 4  illustrates a second method in which tungsten carbide inserts  42  are press-fit into holes  44  formed in the surface  30  near the leading shirttail edge  50 . While these inserts  42  provide better abrasion resistance (in comparison to the use of hardfacing material), the inserts  42  do not provide protection for the leading shirttail edge  50 . The reason for this is that the holes  44  must be located at some appreciable distance from the leading shirttail edge  50  in order for the press-fit to function properly and peripherally retain the inserts  42 . For example, a separation d 2  of at least 0.125 inches is typically provided from the edge of the hole  44  to the leading edge  50 . Thus, the method of  FIG. 4  functions to primarily protect the shirttail region near to, but not exactly at, the leading shirttail edge  50 . Furthermore, in order to be suitably retained, the press-fit inserts  42  must typically have a thickness t (with a corresponding depth of the hole  44 ) such that a ratio of the thickness of the insert to a diameter d′ of the insert (where the inserts are round) or width w of the insert (with other shapes) exceeds about 0.5 (i.e., t/d′≧0.5; or t/w≧0.5). 
     Although not explicitly shown in  FIGS. 3 and 4 , the protection mechanisms shown could alternatively, or additionally, be provided on the leading side surface  54  of the leg  12 . This leading side surface  54  is adjacent the outer surface  30  of the leg  12  at the leading shirttail edge  50 . 
     With reference once again to  FIGS. 1 and 2 , the shoulder surface  25  of the leg  12  laterally terminates at a leading shoulder edge  51  and a trailing shoulder edge  53 . The leading shoulder edge  51  is also susceptible to wear during operation of the rotary cone drill bit  10 , more specifically when the bit  10  is being removed from the drill hole. This is because the shoulder edge  51  may have to function in a cutting-like or abrasive manner to remove formation materials in instances where the drilled hole has narrowed. The leading shoulder edge  51  and shoulder surface  25  are further susceptible to damage from formation material falling in the drill hole and having to be removed. Wear of the leading shoulder edge  51  and shoulder surface  25  can have adverse affects on the opening  29  and the pressure compensation assembly  27  installed within that opening  29  that perhaps lead to premature failure of the lubrication system. 
     A need thus exists in the art to provide an improved method of protecting the leading shirttail edge  50  and leading shoulder edge  51 , as well as the leading side surface  54 , of the leg. 
     SUMMARY 
     In an embodiment, a rotary cone drill bit comprises: a body, a leg depending from the body, a bearing shaft extending from the leg and a cone mounted to the bearing shaft. The leg includes a lateral leading edge. The lateral leading edge may be associated with either (or both) an outer surface of the leg or a shoulder surface of the leg (above the outer surface). A bottom surface of a hard material plate having an edge is attached to a substantially conforming surface of the leg in a position where the edge of the hard material plate defines at least a portion of the lateral leading edge of the leg. 
     In an embodiment, a rotary cone drill bit comprises: a body, a leg depending from the body, a bearing shaft extending from the leg and a cone mounted to the bearing shaft. The leg includes a surface edge that is subject to wear during operation of the bit. The surface edge may be associated with either (or both) an outer surface of the leg or a shoulder surface of the leg (above the outer surface). A bottom surface of a hard material plate having an edge is attached to a substantially conforming surface of the leg in a position where the edge of the hard material plate defines at least a portion of the surface edge of the leg. 
     In any of the foregoing embodiments, the conforming surface to which attachment is made may comprise: a floor surface formed in or by an outer surface of the leg, a floor surface formed in or by a shoulder surface of the leg, a floor surface formed in or by a leading side surface of the leg (adjacent either the outer surface or shoulder surface), a floor surface of a slot formed in the outer surface of the leg, a floor surface of a slot formed in the shoulder surface of the leg, or a floor surface of a slot formed in the leading side surface of the leg (adjacent either the outer surface or shoulder surface). 
     In any of the foregoing embodiments, a material for attaching the hard material plate may comprise a flowable adhesive material interposed between the bottom surface of the hard material plate to the floor surface of the leg. That material may comprise, for example, a brazing material. 
     In any of the foregoing embodiments, the hard material plate may comprise polycrystalline diamond compact, or be made of a material such as solid tungsten carbide, or comprise a polycrystalline cubic boron nitride compact, or comprise an impregnated diamond segment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the invention will become clear in the description which follows of several non-limiting examples, with references to the attached drawings wherein: 
         FIG. 1  illustrates an isometric view of a prior art rotary cone drill bit; 
         FIG. 2  illustrates a cross-sectional view of a portion of a leg of the prior art rotary cone drill bit of  FIG. 1 ; 
         FIG. 3  illustrates application of a layer of hardfacing material extending along at least a portion of the leading edge of the leg; 
         FIG. 4  illustrates the use of tungsten carbide inserts near the leading edge of the leg; 
         FIG. 5  illustrates an isometric view of a rotary cone drill bit including protection mechanisms for the leading edges of the leg at the shirttail and shoulder; 
         FIGS. 6 ,  7 ,  8  and  9  illustrate cross-sectional views of a portion of a leg of a rotary cone drill bit which include embodiments of a mechanism for protecting the leading edge of the leg at the shirttail and shoulder; 
         FIG. 10  illustrates an isometric view of a rotary cone drill bit including protection mechanisms for the leading edges of the leg at the shirttail and shoulder; and 
         FIGS. 11 ,  12 ,  13  and  14  illustrate cross-sectional views of a portion of a leg of a rotary cone drill bit which include embodiments of a mechanism for protecting the leading edge of the leg at the shirttail and shoulder. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Reference is now made to  FIG. 5  which illustrates an isometric view of a rotary cone drill bit  110  including protection mechanisms for the leading edge (also referred to as the lateral leading edge) of the leg. A leg  112  depends from a body portion  114  of the drill bit  110 . The leg  112  includes a bearing shaft (not shown, see  FIG. 2  reference  16 ) which extends in a downward and radial inward direction. A cutter cone  120  is mounted to the bearing shaft and supported thereon for rotation. The outer gage or shirttail surface  130  of the leg  112  (located at the gage of the bit) terminates at a semicircular edge  132  proximal to the cone  120 . The region of the leg  112  associated with the surface  130  is known in the art as the “shirttail region,” and the edge  132  is known in the art as the “shirttail edge.” The outer gage or shirttail surface  130  of the leg  112  laterally terminates at a leading shirttail edge  150  and a trailing shirttail edge  152 . The lateral leading edge  150  and lateral trailing edge  152  of the shirttail comprise extensions of the shirttail edge  132  extending along the length of the leg  112 . The leg  112  further includes a shoulder surface  125  (positioned above the outer surface  130  and angled inwardly from the outer surface  130 ). The shoulder surface  125  of the leg  112  laterally terminates at a leading shoulder edge  151  and a trailing shoulder edge  153 . The lateral leading edge  151  and lateral trailing edge  153  of the shoulder comprise extensions of the shirttail edges  150  and  152 , respectively, extending along the length of the leg  112  (and may be referred to as the lateral leading edge of the leg  112 ). The leg further includes a leading side surface  154  which is adjacent the outer surface  130  and shoulder surface  125  of the leg  112  at the leading shirttail edge  150  and leading shoulder edge  151 . 
     The illustrated drill bit utilizes a sealed bearing system. The lubrication system includes a pressure compensation assembly  127  installed within an opening  129  formed in the upper shoulder surface  125  of the leg  112 .  FIG. 5  illustrates an implementation wherein the opening  129  is formed exclusively in the shoulder surface  125 . It will be understood, however, that the opening  129  may be formed partially in the shoulder surface  125  and partially in the outer surface  130  of the leg  112  (below shoulder surface  125 ). Alternatively, the opening  129  may be formed exclusively in the outer surface  130 . 
     To protect the lateral leading edge  150  and surface  130  of the leg, a slot  138  is provided in the outer surface  130  of the leg  112  extending inwardly from the leading edge  150 , and a hard plate insert  140  is adhered to a floor surface within the slot  138 . See, also,  FIG. 6 . To protect the lateral leading edge  150  and the leading side surface  154 , a slot  142  is provided in the leading side surface  154  of the leg  112  extending outwardly from the leading edge  150  of the shirttail, and a hard plate insert  144  is adhered to a floor surface within the slot  142 . See, also,  FIG. 7 . To protect the shoulder leading edge  151  and the leading side surface  154 , a slot  142  is provided in the leading side surface  154  of the leg  112  extending outwardly from the shoulder leading edge  151 , and a hard plate insert  144  is adhered to a floor surface within the slot  142 . See, also,  FIG. 8 . To protect the shoulder leading edge  151  and the shoulder surface  125 , a slot  138  is provided in the shoulder surface  125  of the leg  112  extending inwardly from the leading edge  151 , and a hard plate insert  140  is adhered to a floor surface within the slot  138 . See, also,  FIG. 9 . Such an installation on the surface  125 , in some instances, may be impractical because of the size and positioning of the opening  129 . The slots may be milled or cast into the outer surface  130 , shoulder surface  125  and/or leading side surface  154  of the leg  112  at desired positions, specifically positions on the leg which are susceptible to wear during operation of the bit, and may have flat or curved floor surface geometries as desired and which conform with the bottom surfaces of the inserts  140  and  144 . 
     Although multiple protection mechanisms are illustrated in  FIG. 5 , it will be understood that any one or more of the illustrated protection mechanisms may be selected for use on the rotary cone drill bit  110 . Although  FIG. 5  illustrates the use of several hard plate inserts  140  along the leading edge  150 , it will be understood that one slot  138  could instead be provided extending along all or a portion of the leading edge  150 , with a single hard plate insert  140  adhered within the slot  138 . Although  FIG. 5  illustrates the use of several hard plate inserts  144  along the leading edge  150 , it will be understood that one slot  142  could instead be provided extending along all or a portion of the leading edge  150 , with a single hard plate insert  144  adhered within the slot  142 . Although  FIG. 5  illustrates the use of a single hard plate insert  144  along the shoulder leading edge  151 , it will be understood that multiple slots with multiple inserts could be provided and further that one slot  142  could be provided extending along all or a portion of the shoulder leading edge  151 , with a single hard plate insert  144  adhered within the slot  142 . Although  FIG. 5  illustrates the use of a single hard plate insert  140  along the shoulder leading edge  151 , it will be understood that multiple slots with multiple inserts could be provided and further that one slot  138  could be provided extending along all or a portion of the shoulder leading edge  151 , with a single hard plate insert  140  adhered within the slot  138 . In each of the foregoing implementations, the portion of the edge (leading shirttail edge  150  and/or shoulder leading edge  151 ) selected to receive protection would be that portion of the edge which is most susceptible to wear during operation of the rotary cone drill bit  110 . 
     Although  FIG. 5  primarily illustrates the use of polygonal plate inserts, it will be understood that the plate inserts can have any desired shape (including circular shapes, oval shapes, semi-circular shapes, and the like). Furthermore, the plate inserts can be of different sizes, perhaps with size selection depending on placement position. 
     Reference is now made to  FIG. 6  which illustrates a cross-sectional view of a portion of a leg of a rotary cone drill bit which includes an embodiment of a protection mechanism for the lateral leading edge of the leg. In this embodiment, the slot  138  is provided in the outer surface  130  of the leg  112  extending inwardly from the lateral leading edge  150 . The slot  138  may be milled or cast into the outer surface  130  of the leg  112 . The slot  138  is defined by a floor surface  170 , a rear wall  172  and two side walls  174  (see, also,  FIG. 5 ). The hard plate insert  140  is adhered within the slot  138 . In a preferred embodiment, a bottom surface of hard plate insert is adhered to the floor surface  170  of the slot  138 . The means for adhering the bottom surface to the floor surface may, for example, comprise any suitable adhering material which is interposed between the substantially conforming (for example, parallel) surfaces including adhesive material flowable between the substantially conforming surfaces by capillary action such as a brazing material, solder, adhesives, resins, and the like (see, for example, U.S. Patent Application Publication No. 2009/0038442, the disclosure of which is hereby incorporated by reference). Because of drawing scale, the adhesive material is not explicitly shown in  FIG. 6 , but it will be understood that the adhesive material is present between the bottom surface and the floor surface. The adhesive material preferably has a substantially uniform thickness between the conforming bottom surface and floor surface. The hard plate insert  140  has a thickness such that when adhered within the slot  138 , a top surface  176  of the plate insert  140  is substantially flush with, or slightly exposed beyond, or slightly recessed below, the outer surface  130  of the leg  112 . Furthermore, the hard plate insert  140  is sized such that an edge  178  of the plate insert opposite the rear wall  172  of the slot  138  defines (or is coincident with or nearly coincident with) the leading edge  150  (leading surface  154 ) of the shirttail. The hard plate insert  140  is made of a material or combination of materials which are more abrasion resistant than the material used to make the leg and shirttail of the bit. In a preferred implementation, the hard plate insert is made of a material such as tungsten carbide, polycrystalline diamond compact (PDC), polycrystalline cubic boron nitride compact impregnated diamond segment, and the like. These materials are superior to the traditional weld on tungsten carbide hardfacing known in the prior art because they are denser and are not as susceptible to abrasion and erosion. Again, the adhesive material is this implementation is not externally exposed and subject to possible wear. 
     The hard plate inserts  140  have a thickness t and width w (wherein the width is measured in a direction perpendicular to the leading edge  150 ). The hard plate inserts  140  are thin inserts. In this case, a ratio of the thickness t of the insert to a width w of the insert is less than 0.5 (i.e., t/w&lt;0.5). More particularly, the ratio of the thickness t of the insert to the width w of the insert is substantially less than 0.5 (i.e., t/w&lt;&lt;0.5). Even more particularly, the ratio of the thickness t of the insert to the width w of the insert is less than 0.2 (i.e., t/w&lt;0.2), and may even be less than 0.1 (i.e., t/w&lt;0.1). This is permitted because the hard plate inserts  140  are retained by adhesion to their bottom surface and not their peripheral edge (as is the case with the press-fit inserts used in the prior art (see,  FIG. 4 ). 
     Reference is now made to  FIG. 7  which illustrates a cross-sectional view of a portion of a leg of a rotary cone drill bit which includes an embodiment of a protection mechanism for the lateral leading edge of the leg. In this embodiment, the slot  142  is provided in the leading side surface  154  of the leg  112  extending outwardly from the lateral leading edge  150 . The slot  142  may be milled or cast into the leading side surface  154  of the leg  112 . The slot  142  is defined by a floor surface  180 , a rear wall  182  and two side walls  184  (see, also,  FIG. 5 ). The hard plate insert  144  is adhered within the slot  142 . In a preferred embodiment, a bottom surface of hard plate insert is adhered to the floor surface  180  of the slot  142 . The means for adhering the bottom surface to the floor surface may, for example, comprise any suitable adhering material which is interposed between the substantially conforming (for example, parallel) surfaces including adhesive material flowable between the substantially conforming surfaces by capillary action such as a brazing material, solder, adhesives, resins, and the like (see, for example, U.S. Patent Application Publication No. 2009/0038442, the disclosure of which is hereby incorporated by reference). The adhesive material preferably has a substantially uniform thickness between the conforming bottom surface and floor surface. Because of drawing scale, the adhesive material is not explicitly shown in  FIG. 7 , but it will be understood that the adhesive material is present between the bottom surface and the floor surface. The hard plate insert  144  has a thickness such that when adhered within the slot  142 , a top surface  186  of the plate insert  144  is substantially flush with, or slightly exposed beyond, or slightly recessed below, the leading side surface  154  of the leg  112 . Furthermore, the hard plate insert  144  is sized such that edge  188  of the plate insert opposite the rear wall  172  of the slot  138  defines (or is coincident with or nearly coincident with) the leading edge  150  (outer surface  130 ). The hard plate insert  140  is made of a material or combination of materials which are more abrasion resistant than the material used to make the leg and shirttail of the bit. In a preferred implementation, the hard plate insert is made of a material such as tungsten carbide, polycrystalline diamond compact (PDC), polycrystalline cubic boron nitride compact impregnated diamond segment, and the like. These materials are superior to the traditional weld on tungsten carbide hardfacing known in the prior art because they are denser and are not as susceptible to abrasion and erosion. Again, the adhesive material is this implementation is not externally exposed and subject to possible wear. 
     The hard plate inserts  144  have a thickness t and width w (wherein the width is measured in a direction perpendicular to the leading edge  150 ). The hard plate inserts  144  are thin inserts. In this case, a ratio of the thickness t of the insert to a width w of the insert to is less than 0.5 (i.e., t/w&lt;0.5). More particularly, the ratio of the thickness t of the insert to the width w of the insert is substantially less than 0.5 (i.e., t/w&lt;&lt;0.5). Even more particularly, the ratio of the thickness t of the insert to the width w of the insert is less than 0.2 (i.e., t/w&lt;0.2), and may even be less than 0.1 (i.e., t/w&lt;0.1). This is permitted because the hard plate inserts  144  are retained by adhesion to their bottom surface and not their peripheral edge (as is the case with the press-fit inserts used in the prior art (see,  FIG. 4 ). 
     Reference is now made to  FIG. 8  which illustrates a cross-sectional view of a portion of a leg of a rotary cone drill bit which includes an embodiment of a protection mechanism for the shoulder lateral leading edge  151 . In this embodiment, the slot  142  is provided in the leading side surface  154  of the leg  112  extending outwardly from the shoulder lateral leading edge  151 . The slot  142  may be milled or cast into the leading side surface  154  of the leg  112 . The slot  142  is defined by a floor surface  180 , a rear wall  182  and two side walls  184  (see, also,  FIG. 5 ). The hard plate insert  144  is adhered within the slot  142 . In a preferred embodiment, a bottom surface of hard plate insert is adhered to the floor surface  180  of the slot  142 . The means for adhering the bottom surface to the floor surface may, for example, comprise any suitable adhering material which is interposed between the substantially conforming (for example, parallel) surfaces including adhesive material flowable between the substantially conforming surfaces by capillary action such as a brazing material, solder, adhesives, resins, and the like (see, for example, U.S. Patent Application Publication No. 2009/0038442, the disclosure of which is hereby incorporated by reference). The adhesive material preferably has a substantially uniform thickness between the conforming bottom surface and floor surface. Because of drawing scale, the adhesive material is not explicitly shown in  FIG. 8 , but it will be understood that the adhesive material is present between the bottom surface and the floor surface. The hard plate insert  144  has a thickness such that when adhered within the slot  142 , a top surface  186  of the plate insert  144  is substantially flush with, or slightly exposed beyond, or slightly recessed below, the leading side surface  154  of the leg  112 . Furthermore, the hard plate insert  144  is sized such that edge  188  of the plate insert opposite the rear wall  172  of the slot  138  defines (or is coincident with or nearly coincident with) the leading edge  151  (shoulder surface  125 ). The hard plate insert  140  is made of a material or combination of materials which are more abrasion resistant than the material used to make the leg and shirttail of the bit. In a preferred implementation, the hard plate insert is made of a material such as tungsten carbide, polycrystalline diamond compact (PDC), polycrystalline cubic boron nitride compact impregnated diamond segment, and the like. These materials are superior to the traditional weld on tungsten carbide hardfacing known in the prior art because they are denser and are not as susceptible to abrasion and erosion. Again, the adhesive material is this implementation is not externally exposed and subject to possible wear. 
     The hard plate inserts  144  have a thickness t and width w (wherein the width is measured in a direction perpendicular to the leading edge  151 ). The hard plate inserts  144  are thin inserts. In this case, a ratio of the thickness t of the insert to a width w of the insert to is less than 0.5 (i.e., t/w&lt;0.5). More particularly, the ratio of the thickness t of the insert to the width w of the insert is substantially less than 0.5 (i.e., t/w&lt;&lt;0.5). Even more particularly, the ratio of the thickness t of the insert to the width w of the insert is less than 0.2 (i.e., t/w&lt;0.2), and may even be less than 0.1 (i.e., t/w&lt;0.1). This is permitted because the hard plate inserts  144  are retained by adhesion to their bottom surface and not their peripheral edge (as is the case with the press-fit inserts used in the prior art (see,  FIG. 4 ). 
     Reference is now made to  FIG. 9  which illustrates a cross-sectional view of a portion of a leg of a rotary cone drill bit which includes an embodiment of a protection mechanism for the lateral leading edge of the leg. In this embodiment, the slot  138  is provided in the shoulder surface  125  of the leg  112  extending inwardly from the lateral leading edge  151 . The slot  138  may be milled or cast into the shoulder surface  125  of the leg  112 . The slot  138  is defined by a floor surface  170 , a rear wall  172  and two side walls  174  (see, also,  FIG. 5 ). The hard plate insert  140  is adhered within the slot  138 . In a preferred embodiment, a bottom surface of hard plate insert is adhered to the floor surface  170  of the slot  138 . The means for adhering the bottom surface to the floor surface may, for example, comprise any suitable adhering material which is interposed between the substantially conforming (for example, parallel) surfaces including adhesive material flowable between the substantially conforming surfaces by capillary action such as a brazing material, solder, adhesives, resins, and the like (see, for example, U.S. Patent Application Publication No. 2009/0038442, the disclosure of which is hereby incorporated by reference). Because of drawing scale, the adhesive material is not explicitly shown in  FIG. 9 , but it will be understood that the adhesive material is present between the bottom surface and the floor surface. The adhesive material preferably has a substantially uniform thickness between the conforming bottom surface and floor surface. The hard plate insert  140  has a thickness such that when adhered within the slot  138 , a top surface  176  of the plate insert  140  is substantially flush with, or slightly exposed beyond, or slightly recessed below, the shoulder surface  125  of the leg  112 . Furthermore, the hard plate insert  140  is sized such that an edge  178  of the plate insert opposite the rear wall  172  of the slot  138  defines (or is coincident with or nearly coincident with) the leading edge  151  (leading surface  154 ) of the shirttail. The hard plate insert  140  is made of a material or combination of materials which are more abrasion resistant than the material used to make the leg and shirttail of the bit. In a preferred implementation, the hard plate insert is made of a material such as tungsten carbide, polycrystalline diamond compact (PDC), polycrystalline cubic boron nitride compact impregnated diamond segment, and the like. These materials are superior to the traditional weld on tungsten carbide hardfacing known in the prior art because they are denser and are not as susceptible to abrasion and erosion. Again, the adhesive material is this implementation is not externally exposed and subject to possible wear. 
     The hard plate inserts  140  have a thickness t and width w (wherein the width is measured in a direction perpendicular to the leading edge  151 ). The hard plate inserts  140  are thin inserts. In this case, a ratio of the thickness t of the insert to a width w of the insert is less than 0.5 (i.e., t/w&lt;0.5). More particularly, the ratio of the thickness t of the insert to the width w of the insert is substantially less than 0.5 (i.e., t/w&lt;&lt;0.5). Even more particularly, the ratio of the thickness t of the insert to the width w of the insert is less than 0.2 (i.e., t/w&lt;0.2), and may even be less than 0.1 (i.e., t/w&lt;0.1). This is permitted because the hard plate inserts  140  are retained by adhesion to their bottom surface and not their peripheral edge (as is the case with the press-fit inserts used in the prior art (see,  FIG. 4 ). 
     It will be noted that the slots and plate inserts may be of any selected geometry thus allowing for the application of protection to complex surfaces of the bit. Tiling of the inserts edge-to-edge permits the application of protection to be extended continuously over a complex curved surface. Alternatively, a single insert with a complex curved bottom surface could be provided. 
     The illustration of protection being applied using slots and plate inserts at the leading shirttail edge and/or shoulder leading edge is by way of example only, it being understood that the protection mechanisms described can be applied to any edges of the bit that are susceptible to wear (including the shirttail edge and any trailing edges of the leg). 
     Reference is now made to  FIG. 10  which illustrates an isometric view of a rotary cone drill bit  210  including protection mechanisms for the leading edges of the leg. A leg  212  depends from a body portion  214  of the drill bit  210 . The leg  212  includes a bearing shaft (not shown, see  FIG. 2  reference  16 ) which extends in a downward and radial inward direction. A cutter cone  220  is mounted to the bearing shaft and supported thereon for rotation. The outer gage or shirttail surface  230  of the leg  212  (located at the gage of the bit) terminates at a semicircular edge  232  proximal to the cone  220 . The region of the leg  212  associated with the outer gage or shirttail surface  230  is known in the art as the “shirttail region,” and the edge  232  is known in the art as the “shirttail edge.” The outer surface  230  of the leg  212  laterally terminates at a leading shirttail edge  250  and a trailing shirttail edge  252 . The leading edge  250  and a trailing edge  252  of the shirttail comprise extensions of the shirttail edge  232  extending along the length of the leg  212 . The leg  212  further includes a shoulder surface  225  (above the outer surface  230 ). The shoulder surface  225  of the leg  212  laterally terminates at a leading shoulder edge  251  and a trailing shoulder edge  253 . The lateral leading edge  251  and lateral trailing edge  253  of the shoulder comprise extensions of the shirttail edges  250  and  252 , respectively, extending along the length of the leg  212  (and may be referred to as the lateral leading edge of the leg  212 ). The leg further includes a leading side surface  254  which is adjacent the outer surface  230  and shoulder surface  225  of the leg  212  at the leading shirttail edge  250  and leading shoulder edge  251 . 
     The illustrated drill bit utilizes a sealed bearing system. The lubrication system includes a pressure compensation assembly  127  installed within an opening  129  formed in the upper shoulder surface  225  of the leg  212 .  FIG. 9  illustrates an implementation wherein the opening  129  is formed exclusively in the shoulder surface  225 . It will be understood, however, that the opening  129  may be formed partially in the shoulder surface  225  and partially in the outer surface  230  of the leg  212  (below shoulder surface  225 ). Alternatively, the opening  129  may be formed exclusively in the outer surface  230 . 
     To protect the leading edge  250  and outer surface  230  of the leg  212 , a hard plate  240  is adhered to a floor surface  231  provided in or by the curved outer surface  230  of the leg  212  extending inwardly from the leading edge  250 . See, also,  FIG. 11 . To protect the leading edge  250  and the leading side surface  254 , a hard plate  244  is adhered to a floor surface  231  provided in or by the leading side surface  254  of the leg  212  extending outwardly from the leading edge  250 . See, also,  FIG. 12 . To protect the shoulder leading edge  251  and the leading side surface  254 , a hard plate  244  is adhered to a floor surface  231  provided in or by the leading side surface  254  of the leg  212  extending outwardly from the leading edge  251 . See, also,  FIG. 13 . ***To protect the leading edge  251  and shoulder surface  225  of the leg  212 , a hard plate  240  is adhered to a floor surface  231  provided in or by the curved shoulder surface  225  of the leg  212  extending inwardly from the leading edge  251 . See, also,  FIG. 14 . Such an installation on the shoulder surface  225 , in many instances, may be impractical because of the size and positioning of the opening  129 . 
     Although multiple protection mechanisms are illustrated in  FIG. 10 , it will be understood that any one or more of the illustrated protection mechanisms may be selected for use on the rotary cone drill bit  210 . The floor surfaces  231  are preferably machined or cast into the outer surfaces of the shirttail region along the edge  250  and edge  251 , and may have flat or curved surface geometries as desired and which conform with the bottom surfaces of the plates  240  and  244 . 
     Although  FIG. 10  primarily illustrates the use of polygonal plates, it will be understood that the plates can have any desired shape (including circular shapes, oval shapes, semi-circular shapes, and the like). Furthermore, the plates can be of different sizes, perhaps with size selection depending on placement position. 
     Although  FIG. 10  illustrates the use of several hard plates  240  along the leading edge  250 , it will be understood that one plate  240  could instead be provided extending along all or a portion of the leading edge  250 . Although  FIG. 10  illustrates the use of several hard plates  244  along the leading edge  250 , it will be understood that one plate  244  could instead be provided extending along all or a portion of the leading edge  250 . Although  FIG. 10  illustrates the use of a single hard plate  244  along the leading edge  251 , it will be understood that multiple plates  244  could instead be provided or that a single plate extending along all or a portion of the leading edge  251  could be used. Although  FIG. 10  illustrates the use of a single hard plate  240  along the leading edge  251 , it will be understood that multiple plates  240  could instead be provided or that a single plate extending along all or a portion of the leading edge  251  could be used. In each of the foregoing implementations, the portion of the edge (edge  250  and/or edge  251 ) selected to receive protection would be that portion of the edge which is most susceptible to wear during operation of the rotary cone drill bit  210 . 
     Reference is now made to  FIG. 11  which illustrates a cross-sectional view of a portion of a leg of a rotary cone drill bit which includes an embodiment of a protection mechanism for the leading edge. In this embodiment, the bottom surface  270  of the hard plate  240  is adhered to a substantially conforming floor surface  231  formed in or by the outer surface  230  of the leg  212  and extending inwardly from the leading shirttail edge  250 . The plate  240  is further defined by a rear edge  272  and two side edges  274  (see, also,  FIG. 10 ). The means for adhering the bottom surface to the floor surface may, for example, comprise any suitable adhering material which is interposed between the substantially conforming (for example, parallel) surfaces including adhesive material flowable between the substantially conforming surfaces by capillary action such as a brazing material, solder, adhesives, resins, and the like (see, for example, U.S. Patent Application Publication No. 2009/0038442, the disclosure of which is hereby incorporated by reference). Because of drawing scale, the adhesive material is not explicitly shown in  FIG. 11 , but it will be understood that the adhesive material is present between the bottom surface and the flattened surface. The adhesive material preferably has a substantially uniform thickness between the conforming bottom surface and floor surface. The hard plate  240  is sized such that its front edge  278  defines (or is coincident with, or is nearly coincident with) the leading edge  250  of the shirttail. The thickness of the plate  240  may range from 0.050 to 0.500 inches. The hard plate  240  is made of a material or combination of materials which are more abrasion resistant than the material used to make the leg and shirttail of the bit. In a preferred implementation, the hard plate is made of a material such as tungsten carbide, PDC, polycrystalline cubic boron nitride compact impregnated diamond segment, and the like. These materials are superior to the traditional weld on tungsten carbide hardfacing known in the prior art because they are denser and are not as susceptible to abrasion and erosion. Again, the adhesive material is this implementation is not externally exposed and subject to possible wear. The conforming surfaces where adhesion takes place may curve, for example, with the radius of the bit, or have any selected curved configuration. 
     The hard plates  240  have a thickness t and width w (wherein the width is measured in a direction perpendicular to the leading edge  250 ). The hard plates  240  are thin inserts. In this case, a ratio of the thickness t of the plate to a width w of the plate is less than 0.5 (i.e., t/w&lt;0.5). More particularly, the ratio of the thickness t of the plate to the width w of the plate is substantially less than 0.5 (i.e., t/w&lt;&lt;0.5). Even more particularly, the ratio of the thickness t of the plate to the width w of the plate is less than 0.2 (i.e., t/w&lt;0.2), and may even be less than 0.1 (i.e., t/w&lt;0.1). 
     Reference is now made to  FIG. 12  which illustrates a cross-sectional view of a portion of a leg of a rotary cone drill bit which includes an embodiment of a protection mechanism for the leading edge. In this embodiment, the bottom surface  280  of the hard plate  244  is adhered to a substantially conforming floor surface  231  formed in or by the leading surface  254  of the leg  212  and extending outwardly from the leading shirttail edge  250 . The plate  244  is further defined by a rear edge  282  and two side edges  284  (see, also,  FIG. 10 ). The means for adhering the bottom surface to the floor surface may, for example, comprise any suitable adhering material which is interposed between the substantially conforming (for example, parallel) surfaces including adhesive material flowable between the substantially conforming surfaces by capillary action such as a brazing material, solder, adhesives, resins, and the like (see, for example, U.S. Patent Application Publication No. 2009/0038442, the disclosure of which is hereby incorporated by reference). Because of drawing scale, the adhesive material is not explicitly shown in  FIG. 12 , but it will be understood that the adhesive material is present between the bottom surface and the flattened surface on the leading side surface. The adhesive material preferably has a substantially uniform thickness between the conforming bottom surface and floor surface. The hard plate  244  is sized such that its front edge  288  defines (or is coincident with, or is nearly coincident with) the leading edge  250  of the shirttail. The thickness of the plate  244  may range from 0.050 to 0.500 inches. The hard plate  244  is made of a material or combination of materials which are more abrasion resistant than the material used to make the leg and shirttail of the bit. In a preferred implementation, the hard plate is made of a material such as tungsten carbide, PDC, polycrystalline cubic boron nitride compact impregnated diamond segment, and the like. These materials are superior to the traditional weld on tungsten carbide hardfacing known in the prior art because they are denser and are not as susceptible to abrasion and erosion. Again, the adhesive material is this implementation is not externally exposed and subject to possible wear. The conforming surfaces where adhesion takes place may curve, for example, with the radius of the bit, or have any selected curved configuration. 
     The hard plates  244  have a thickness t and width w (wherein the width is measured in a direction perpendicular to the leading edge  250 ). The hard plates  244  are thin inserts. In this case, a ratio of the thickness t of the plate to a width w of the plate is less than 0.5 (i.e., t/w&lt;0.5). More particularly, the ratio of the thickness t of the plate to the width w of the plate is substantially less than 0.5 (i.e., t/w&lt;&lt;0.5). Even more particularly, the ratio of the thickness t of the plate to the width w of the plate is less than 0.2 (i.e., t/w&lt;0.2), and may even be less than 0.1 (i.e., t/w&lt;0.1). 
     Reference is now made to  FIG. 13  which illustrates a cross-sectional view of a portion of a leg of a rotary cone drill bit which includes an embodiment of a protection mechanism for the leading edge of the shoulder  225 . In this embodiment, the bottom surface  280  of the hard plate  244  is adhered to a substantially conforming floor surface  231  formed in or by the leading surface  254  of the leg  212  and extending outwardly from the leading shoulder edge  251 . The plate  244  is further defined by a rear edge  282  and two side edges  284  (see, also,  FIG. 10 ). The means for adhering the bottom surface to the floor surface may, for example, comprise any suitable adhering material which is interposed between the substantially conforming (for example, parallel) surfaces including adhesive material flowable between the substantially conforming surfaces by capillary action such as a brazing material, solder, adhesives, resins, and the like (see, for example, U.S. Patent Application Publication No. 2009/0038442, the disclosure of which is hereby incorporated by reference). Because of drawing scale, the adhesive material is not explicitly shown in  FIG. 13 , but it will be understood that the adhesive material is present between the bottom surface and the flattened surface on the leading side surface. The adhesive material preferably has a substantially uniform thickness between the conforming bottom surface and floor surface. The hard plate  244  is sized such that its front edge  288  defines (or is coincident with, or is nearly coincident with) the leading edge  251 . The thickness of the plate  244  may range from 0.050 to 0.500 inches. The hard plate  244  is made of a material or combination of materials which are more abrasion resistant than the material used to make the leg and shirttail of the bit. In a preferred implementation, the hard plate is made of a material such as tungsten carbide, PDC, polycrystalline cubic boron nitride compact impregnated diamond segment, and the like. These materials are superior to the traditional weld on tungsten carbide hardfacing known in the prior art because they are denser and are not as susceptible to abrasion and erosion. Again, the adhesive material is this implementation is not externally exposed and subject to possible wear. The conforming surfaces where adhesion takes place may curve, for example, with the radius of the bit, or have any selected curved configuration. 
     The hard plates  244  have a thickness t and width w (wherein the width is measured in a direction perpendicular to the leading edge  251 ). The hard plates  244  are thin inserts. In this case, a ratio of the thickness t of the plate to a width w of the plate is less than 0.5 (i.e., t/w&lt;0.5). More particularly, the ratio of the thickness t of the plate to the width w of the plate is substantially less than 0.5 (i.e., t/w&lt;&lt;0.5). Even more particularly, the ratio of the thickness t of the plate to the width w of the plate is less than 0.2 (i.e., t/w&lt;0.2), and may even be less than 0.1 (i.e., t/w&lt;0.1). 
     Reference is now made to  FIG. 14  which illustrates a cross-sectional view of a portion of a leg of a rotary cone drill bit which includes an embodiment of a protection mechanism for the leading edge. In this embodiment, the bottom surface  270  of the hard plate  240  is adhered to a substantially conforming floor surface  231  formed in or by the shoulder surface  225  of the leg  212  and extending inwardly from the leading edge  251 . The plate  240  is further defined by a rear edge  272  and two side edges  274  (see, also,  FIG. 10 ). The means for adhering the bottom surface to the floor surface may, for example, comprise any suitable adhering material which is interposed between the substantially conforming (for example, parallel) surfaces including adhesive material flowable between the substantially conforming surfaces by capillary action such as a brazing material, solder, adhesives, resins, and the like (see, for example, U.S. Patent Application Publication No. 2009/0038442, the disclosure of which is hereby incorporated by reference). Because of drawing scale, the adhesive material is not explicitly shown in  FIG. 14 , but it will be understood that the adhesive material is present between the bottom surface and the flattened surface. The adhesive material preferably has a substantially uniform thickness between the conforming bottom surface and floor surface. The hard plate  240  is sized such that its front edge  278  defines (or is coincident with, or is nearly coincident with) the leading edge  251 . The thickness of the plate  240  may range from 0.050 to 0.500 inches. The hard plate  240  is made of a material or combination of materials which are more abrasion resistant than the material used to make the leg and shirttail of the bit. In a preferred implementation, the hard plate is made of a material such as tungsten carbide, PDC, polycrystalline cubic boron nitride compact impregnated diamond segment, and the like. These materials are superior to the traditional weld on tungsten carbide hardfacing known in the prior art because they are denser and are not as susceptible to abrasion and erosion. Again, the adhesive material is this implementation is not externally exposed and subject to possible wear. The conforming surfaces where adhesion takes place may curve, for example, with the radius of the bit, or have any selected curved configuration. 
     The hard plates  240  have a thickness t and width w (wherein the width is measured in a direction perpendicular to the leading edge  251 ). The hard plates  240  are thin inserts. In this case, a ratio of the thickness t of the plate to a width w of the plate is less than 0.5 (i.e., t/w&lt;0.5). More particularly, the ratio of the thickness t of the plate to the width w of the plate is substantially less than 0.5 (i.e., t/w&lt;&lt;0.5). Even more particularly, the ratio of the thickness t of the plate to the width w of the plate is less than 0.2 (i.e., t/w&lt;0.2), and may even be less than 0.1 (i.e., t/w&lt;0.1). 
     It will be noted that the hard plates may be of any selected geometry thus allowing for the application of protection to complex surfaces of the bit. 
     The illustration of protection being applied using plates at the leading shoulder edge and/or leading shirttail edge is by way of example only, it being understood that the protection mechanisms described can be applied to any edge of the bit that are susceptible to wear (including shirttail edges and trailing edges). 
     Although preferred embodiments of the method and apparatus have been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.