Patent Publication Number: US-2015063931-A1

Title: Indexable drill assembly and drill body having coolant supply

Description:
BACKGROUND 
     The present invention pertains to an indexable drill assembly, as well as the drill body of the indexable drill assembly, useful for the drilling of holes in a workpiece. More specifically, the invention pertains to an indexable drill assembly, as well as the drill body of the indexable drill assembly, useful for the drilling of holes in a workpiece adapted to facilitate enhanced delivery of coolant adjacent the interface between the workpiece and each one of the outboard cutting insert and the inboard cutting insert (insert-chip interface) so as to provide cooling thereby diminishing tremendous heat and also providing lubrication at the insert-chip interface in a hole drilling operation. 
     Indexable drill assemblies useful for the drilling of holes in a workpiece generally include an outboard cutting insert and an inboard cutting insert wherein each cutting insert has a surface terminating at a cutting edge. The indexable drill further includes a tool holder formed with a seat adapted to receive the insert. Each cutting insert engages a workpiece to remove material, and in the process forms chips of the material. Excessive heat at the insert-chip interface can negatively impact upon (i.e., reduce or shorten) the useful tool life of each cutting insert. 
     For example, a chip generated from the workpiece can sometimes stick (e.g., through welding) to the surface of the cutting insert. The build up of chip material on the cutting insert in this fashion is an undesirable occurrence that can negatively impact upon the performance of the cutting insert, and hence, the overall drilling operation. A flow of coolant to the insert-chip interface will reduce the potential for such welding. It would therefore be desirable to reduce excessive heat at the insert-chip interface to eliminate or reduce build up of chip material. 
     As another example, in a chipforming drilling operation, there can occur instances in which the chips do not exit the region of the insert-chip interface when the chip sticks to the cutting insert. When a chip does not exit the region of the insert-chip interface, there is the potential that a chip can be re-cut. It is undesirable for the cutting insert to re-cut a chip already removed from the workpiece. A flow of coolant to the insert-chip interface will facilitate the evacuation of chips from the insert-chip interface thereby minimizing the potential that a chip will be re-cut during the drilling operation. 
     There is an appreciation that a shorter useful tool life increases operating costs and decreases overall production efficiency. Excessive heat at the insert-chip interface contribute to the welding of chip material and re-cutting of chips, both of which are detrimental to production efficiency. There are readily apparent advantages connected with decreasing the heat at the insert-chip interface wherein one way to decrease the temperature is to supply coolant to the insert-chip interface. 
     Heretofore, cutting inserts useful in material removal applications have provided for the delivery of coolant to the region of the insert-chip interface. The following patent documents are exemplary of some earlier efforts. 
     U.S. Pat. No. 6,123,488 to Kasperik et al. pertains to a cutting insert that contains a central aperture defined by an aperture wall. In the Kasperik et al. patent, the aperture wall contains protrusions that function to assist the operator to identify the specific cutting insert. U.S. Pat. No. 7,198,437 to Jonsson (also U.S. Reissue Pat. No. Re 42,644 E) discloses a round cutting insert-round shim assembly. The bottom surface of the cutting insert contains radial indexing portions and the top surface contains swirled chip breakers. U.S. Pat. No. 7,677,842 to Park shows a cutting insert that contains a central aperture defined by a wall. The wall has clearance portions that render the aperture non-circular. 
     United States Patent Application Publication No. US 2001/0027021 to Nelson et al. shows a round cutting insert that includes a base member having central aperture wherein a core member is in the central aperture. An interior coolant passage is defined between the core and the surface that defines the central aperture. United States Patent Application Publication No. US2009/0123244 to Beuttiker et al. pertains to a machine reamer that includes coolant flow passages around a screw (34) with the flow of coolant (apparently indicated by the arrows 78) in a coolant bore (66). See FIG. 1d. 
     U.S. Pat. No. 7,997,832 B2 to Prichard et al. discloses a cutting insert that contains interior coolant channels for delivery of coolant to the vicinity of the intersection of the cutting insert and the workpiece. In one embodiment, the cutting insert comprises a diverter plate that attaches to a milling insert body (e.g., see FIG. 7). In another embodiment, a milling insert body receives opposite rake plates (e.g., see FIG. 16). In still another embodiment, a milling insert body receives a milling rake plate (e.g., see FIGS. 19-22). 
     U.S. Pat. No. 7,125,207 to Craig et al. discloses a tool holder that carries cutting inserts. The tool holder contains an integral coolant channel. The integral coolant channel provides for the delivery of coolant to the cutting inserts. United States Patent Application Publication No. US 2011/0229277 A1 to Hoffer et al., and assigned to Kennametal Inc. (the assignee of the present invention) discloses a round cutting insert that includes distinct interior coolant passages that provide for the flow of coolant to the cutting edge of the insert. In one embodiment, the round cutting insert includes a base member that receives a core member. The distinct interior coolant passages are defined between the base member and the core member. 
     United States Patent Application Publication No. US2011/0020072 to Chen et al. shows a cutting insert and a cutting insert-shim assembly. The cutting insert contains a plurality of distinct coolant passages. The shim contains an opening that facilitates coolant flow to the cutting insert. United States Patent Application Publication No. US2010/00272529 to Rozzi et al. shows a rotary cutting tool in which there is coolant delivery to the pocket regions thereof. An integral cooling channel branches into a direct cooling channel in communication with a jet opening ad an indirect cooling channel that has an opening in the tool pocket. U.S. Pat. No. 6,595,727 B2 to Arvidsson shows a tool for chip-removing machining that provides coolant to a plurality of the cutting inserts via fluid-conducting grooves. 
     U.S. Pat. No. 5,346,335 to Harpaz et al. shows a cutting insert with a recessed portion. A through-going bore extends through the cutting insert including in the vicinity of the recessed portion. Coolant flows through the through-going bore to provide coolant to the cutting insert. Japanese Patent Application Publication JP 5-301104 (assigned to Sumitomo Electric Ind. Ltd.) shows a cutting insert that contains a plurality of interior cooling channels. United States Patent Application Publication No. US 2011/0020077 to Fouqyer shows a hollow clamping screw having an axial channel that carries lubricating fluid. The fluid apparently sprays on the cutting insert (e.g., see FIG. 9). 
     SUMMARY OF THE INVENTION 
     In one form thereof, the invention is an indexable drill assembly. The assembly includes a drill body, which has a head portion at the axial forward end thereof, and the head portion has an outboard pocket and an inboard pocket. The drill body further contains an outboard pocket coolant channel adjacent the outboard pocket, and an inboard pocket coolant channel adjacent the inboard pocket. The outboard pocket has a seating surface wherein the outboard pocket coolant channel opening at the seating surface. The drill body further contains an outboard retention screw aperture opening in the seating surface. The seating surface contains an outboard coolant ring surrounding the retention screw aperture wherein the outboard coolant ring is in fluid communication with the outboard pocket coolant channel. The inboard pocket has a seating surface wherein the inboard pocket coolant channel opening at the seating surface. The drill body further contains an inboard retention screw aperture opening in the seating surface. The seating surface contains an inboard coolant ring surrounding the inboard retention screw aperture wherein the inboard coolant ring is in fluid communication with the inboard pocket coolant channel. The assembly includes an indexable outboard cutting insert retained in the outboard pocket, and an indexable inboard cutting insert retained in the inboard pocket. 
     In yet another form thereof, the invention is an indexable drill assembly that includes a drill body, which has a head portion at the axial forward end thereof, and the head portion has an outboard pocket and an inboard pocket. The drill body further contains an outboard pocket coolant channel adjacent the outboard pocket, and an inboard pocket coolant channel adjacent the inboard pocket. The outboard pocket has a seating surface wherein the outboard pocket coolant channel opening at the seating surface. The drill body further contains an outboard retention screw aperture opening in the seating surface. The seating surface contains an outboard coolant ring surrounding the retention screw aperture wherein the outboard coolant ring is in fluid communication with the outboard pocket coolant channel. The inboard pocket has a seating surface wherein the inboard pocket coolant channel opening at the seating surface. The drill body further contains an inboard retention screw aperture opening in the seating surface. The seating surface contains an inboard coolant ring surrounding the inboard retention screw aperture wherein the inboard coolant ring is in fluid communication with the inboard pocket coolant channel. The assembly further includes an indexable outboard cutting insert that has an outboard primary coolant trough corresponding to each of at least a pair of adjacent discrete corners. The indexable outboard cutting insert is retained in the outboard pocket such that the outboard cutting insert is pulled-back toward the notch whereby less coolant flows through the outboard primary coolant trough corresponding to the discrete corners adjacent the notch of the outboard pocket. The assembly also includes an indexable inboard cutting insert that has an inboard primary coolant trough corresponding to each of at least a pair of adjacent discrete corners. The indexable inboard cutting insert is retained in the inboard pocket such that the inboard cutting insert is pulled-back toward the notch whereby less coolant flows through the inboard primary coolant trough corresponding to the discrete corners adjacent the notch of the inboard pocket. 
     In still another form thereof, the invention is a drill body which has a head portion at the axial forward end thereof, and the head portion has an outboard pocket and an inboard pocket. The drill body further contains an outboard pocket coolant channel adjacent the outboard pocket, and an inboard pocket coolant channel adjacent the inboard pocket. The outboard pocket has a seating surface wherein the outboard pocket coolant channel opening at the seating surface. The drill body further contains an outboard retention screw aperture opening in the seating surface. The seating surface contains an outboard coolant ring surrounding the retention screw aperture wherein the outboard coolant ring is in fluid communication with the outboard pocket coolant channel. The inboard pocket has a seating surface wherein the inboard pocket coolant channel opening at the seating surface. The drill body further contains an inboard retention screw aperture opening in the seating surface. The seating surface contains an inboard coolant ring surrounding the inboard retention screw aperture wherein the inboard coolant ring is in fluid communication with the inboard pocket coolant channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following is a brief description of the drawings that form a part of this patent application: 
         FIG. 1  is an isometric view of a specific embodiment of the indexable drill assembly along with a workpiece; 
         FIG. 2  is an isometric view of the outboard pocket of the indexable drill body without an outboard cutting insert within the outboard pocket; 
         FIG. 3  is an isometric view of the inboard pocket of the indexable drill body without an inboard cutting insert within the inboard pocket; 
         FIG. 4 . is an isometric view of the indexable outboard cutting insert showing the rake surface of the indexable outboard cutting insert; 
         FIG. 4A  is an isometric view of one outboard primary coolant trough of the outboard cutting insert; 
         FIG. 5 . is an isometric view of the outboard cutting insert showing the bottom surface of the outboard cutting insert; 
         FIG. 6 . is an isometric view of the indexable inboard cutting insert showing the rake surface of the indexable inboard cutting insert; 
         FIG. 6A  is an isometric view of one inboard primary coolant trough of the inboard cutting insert; 
         FIG. 7 . is an isometric view of the inboard cutting insert showing the bottom surface of the inboard cutting insert; 
         FIG. 8  is an isometric view of the outboard retention screw; 
         FIG. 9  is a side view of the outboard retention screw; 
         FIG. 10  is an isometric view of the inboard retention screw; 
         FIG. 11  is a side view of the inboard retention screw; 
         FIG. 12  is an isometric view of the outboard cutting insert received within the outboard pocket of the indexable drill body, but without the outboard retention screw in position; 
         FIG. 13  is an isometric view of the outboard cutting insert received within the outboard pocket of the indexable drill body wherein the outboard retention screw secures the outboard cutting insert in position in the outboard pocket; 
         FIG. 13A  is a cross-sectional view of the outboard cutting insert received within the outboard pocket of the indexable drill body of  FIG. 13  taken along section line  13 A- 13 A of  FIG. 13 ; 
         FIG. 14  is an isometric view of the inboard cutting insert received within the inboard pocket of the indexable drill body, but without the inboard retention screw in position; 
         FIG. 15  is an isometric view of the inboard cutting insert received within the inboard pocket of the indexable drill body wherein the inboard retention screw secures the inboard cutting insert in position in the inboard pocket; 
         FIG. 15A  is a cross-sectional view of the inboard cutting insert received within the outboard pocket of the indexable drill body of  FIG. 15  taken along section line  15 A- 15 A of  FIG. 15 ; 
         FIG. 16  is an isometric schematic view showing the flow of coolant through the axial forward portion of the indexable drill body and into the outboard pocket and then into the indexable outboard cutting insert; 
         FIG. 17  is a schematic top view showing the coolant flow out of the outboard cutting insert when secure din the outboard pocket; 
         FIG. 18  is an isometric schematic view showing the flow of coolant through the axial forward portion of the indexable drill body and into the inboard pocket and then into the inboard cutting insert; 
         FIG. 19  is a schematic top view showing the coolant flow out of the inboard cutting insert; 
         FIG. 20  is an isometric view of another specific embodiment of a rectangular cutting insert; 
         FIG. 20A  is an isometric view of one outboard primary coolant trough of the cutting insert of  FIG. 20 ; 
         FIG. 21  is an isometric view of the cutting insert of  FIG. 20  showing the bottom surface of the cutting insert; and 
         FIG. 22  is a top view of the cutting insert of  FIG. 20  showing the rake surface of the inboard cutting insert. 
     
    
    
     DETAILED DESCRIPTION 
     As described hereinabove, the present invention pertains to an indexable drill assembly, as well as the drill body of the indexable drill assembly, useful for the drilling of holes in a workpiece. More specifically, the invention pertains to an indexable drill assembly, as well as the drill body of the indexable drill assembly, useful for the drilling of holes in a workpiece adapted to facilitate enhanced delivery of coolant adjacent (or proximate) the interface between the workpiece and each one of the outboard cutting insert and the inboard cutting insert (insert-chip interface) so as to provide cooling thereby diminishing tremendous heat and also providing lubrication at the insert-chip interface in a hole drilling operation. Delivery of coolant to the insert-chip interface is especially beneficial in drilling long-chipping materials, such as, for example, low carbon steel, stainless steel, and high temperature alloys. 
     Excessive heat at the insert-chip interface contribute to the welding of chip material and re-cutting of chips, both of which are detrimental to production efficiency. There is an appreciation that a shorter useful tool life increases operating costs and decreases overall production efficiency. It therefore becomes readily apparent that there are advantages connected with decreasing the heat due to high cutting temperatures at the insert-chip interface wherein one way to decrease the temperature is to supply coolant to the insert-chip interface. 
     Referring to the drawings,  FIG. 1  illustrates a specific embodiment of the indexable drill assembly generally designated as  40  that is useful to cut material (e.g., drill holes) from a workpiece (e.g., low carbon steel, stainless steel, and high temperature alloys) represented in schematic fashion by  68 . As will become apparent, the indexable drill assembly  40  has a cutting insert orientation wherein a rectangular-shaped cutting insert is the outboard cutting insert  130  and a trigon (or trigonal) cutting insert is the inboard cutting insert  220 . There should be an appreciation that the present invention has application to an indexable drill assembly wherein the outboard cutting insert is a trigon cutting insert and the inboard cutting insert is a rectangular-shaped cutting insert. Further, there should be an appreciation that the present invention has application to an indexable drill assembly that uses two rectangular-shaped cutting inserts wherein each one of the outboard and inboard cutting inserts is rectangular-shaped. Further still, there should be a further appreciation that the present invention has application to an indexable drill assembly that uses two trigon cutting inserts wherein each one of the outboard and inboard cutting inserts is trigonal in shape. The rectangular cutting insert(s) may be of the first specific embodiment cutting insert  130  and/or the second specific embodiment cutting insert  344 . Each one of the first specific embodiment rectangular cutting insert  130  and the second specific embodiment rectangular cutting insert  344  are described in more detail hereinafter. The trigon cutting insert is the specific embodiment of the indexable inboard cutting insert  220 . 
     The indexable drill assembly  40  includes an indexable drill body  42  that has a central longitudinal axis B-B. The indexable drill body  42  has an axial forward end  44  and an axial rearward end  46 . The indexable drill body  42  has a head portion  48 , which is at the axial forward end  44  of the indexable drill body  42 , and a shank portion  52 , which is at the axial rearward end  46  of the indexable drill body  42 . The indexable drill body  42  has a helix portion  50  that is mediate between and contiguous with the head portion  48  and the shank portion  52 . Helical flutes  51  extend in an axial orientation along most of the axial length of the helix portion  50 . The helical flutes  51  facilitate the evacuation of chips generated during the drilling operation via the cutting inserts ( 130 ,  220 ) cutting the workpiece. 
     The indexable drill body  42  contains a body coolant channel  54 , which is an interior channel, that runs along a portion of the axial length of the helix portion  50  and all of the axial length of the shank portion  52  of the indexable drill body  42 . The body coolant channel  54  has an inlet  56  through which coolant (typically under pressure) enters from a coolant source  57 . Coolant source  57  is shown in schematic fashion to be in communication with the body coolant channel  54  via inlet  56 . The indexable drill body  42  further contains an outboard pocket coolant channel  70  that is in fluid communication with the body coolant channel  54 . The outboard pocket coolant channel  70  has a receiving end  74  through which coolant enters from the body coolant channel  54  and a delivery end  72  (see  FIG. 2 ). Coolant passes through the outboard pocket coolant channel  70  exiting the delivery end  72  at the seating surface  66  of the outboard pocket  58 . The indexable drill body  42  also contains an inboard pocket coolant channel  114  that is in fluid communication with the body coolant channel  54 . The inboard pocket coolant channel  114  has a delivery end  116  and a receiving end  118 . The inboard pocket coolant channel  114  receives coolant via the receiving end  118  from the body coolant channel  54 . Coolant passes through the inboard pocket coolant channel  114  exiting the delivery end  116  at the seating surface  108  of the inboard pocket  96  (see  FIG. 3 ). 
     The indexable drill body  42  has an outboard pocket  58  defined by a pair of angularly disposed upstanding walls ( 60 ,  62 ) separated by a notch  64  and a seating surface  66 . There is a retention screw aperture  76  in the seating surface  66  wherein there is a generally circular coolant ring  78  in the seating surface  66  adjacent to the retention screw aperture  76 . As illustrated in  FIG. 2 , there is an intersection between the outboard pocket coolant channel  70  at the delivery end  72  and the coolant ring  78  wherein this intersection is generally designated as  80  in  FIG. 2 . Coolant travels into the coolant ring  78  from the outboard pocket coolant channel  70 . As described hereinafter, the coolant ring  78  cooperates with the indexable outboard cutting insert  130  to form an outboard circular coolant conduit  334  that supplies coolant to the outboard cutting insert  130 . 
     The indexable drill body  42  further has an inboard pocket  96  defined by an upstanding wall  98  and another upstanding wall  102  wherein a side notch  100  separates upstanding walls  98  and  102 , and still another upstanding wall  106  wherein a central notch  104  separates the upstanding wall  102  from upstanding wall  106 . A seating surface  108  further defines the inboard pocket  96 . There is a retention screw aperture  120  in the seating surface  108  wherein there is a coolant ring  122  in the seating surface  108  adjacent to the retention screw aperture  120 . As illustrated in  FIG. 3 , there is an intersection between the inboard pocket coolant channel  114  at the delivery end  116  and the coolant ring  122  wherein this intersection is generally designated as  124  in  FIG. 3 . Coolant travels into the coolant ring  122  from the inboard pocket coolant channel  114 . As described hereinafter, the coolant ring  122  cooperates with the indexable inboard cutting insert  220  to form an inboard circular coolant conduit  340  that supplies coolant to the inboard cutting insert  220 . 
     Referring especially to  FIGS. 4 ,  4 A and  5 , the indexable drill assembly  40  further includes an indexable outboard cutting insert  130 , which exhibits a generally rectangular geometry. The outboard cutting insert  130  has an outboard bottom surface  132  and an outboard rake face  134  as well as outboard flank surfaces  136  that join together the bottom surface  132  and the rake face  134 . The outboard cutting insert  130  contains an outboard central aperture  138  that has a bottom end  140  and a top end  142  and a side wall  144  with a mouth  146  adjacent to and about the circumference of the top end  142 . The mouth  146  has a mouth surface  147 . The outboard cutting insert  130  further contains an annular groove  148  about the bottom end  140  of the outboard central aperture  138 . The rake face  134  intersects with the flank surfaces  136  to form four discrete outboard corners ( 150 ,  152 ,  154 ,  156 ), as well as four discrete outboard cutting edges ( 151 ,  153 ,  155 ,  157 ) of the outboard cutting insert  130 . As one skilled in the art can appreciate, the outboard cutting insert  130  can be indexed to different positions to present a different selected one of the cutting edges ( 151 ,  153 ,  155 ,  157 ) for engagement with the workpiece. Each one of the cutting edges ( 151 ,  153 ,  155 ,  157 ) is defined between adjacent discrete corners ( 150 ,  152 ,  154 ,  156 ). For example, cutting edge  151  is defined as between discrete corners  150  and  152 . 
     The outboard cutting insert  130  contains four outboard primary coolant troughs  160 ,  162 ,  164  and  166  wherein each primary coolant trough corresponds to one of the discrete corners ( 150 ,  152 ,  154 ,  156 ), respectively. For the sake of brevity, a description of one primary coolant trough  160  will suffice for the description of the other three primary coolant troughs ( 162 ,  164 ,  166 ) since the four primary coolant troughs ( 160 ,  162 ,  164 ,  166 ) are substantially identical. 
     Referring to  FIG. 4A , primary coolant trough  160  has an aperture section  170  of the primary coolant trough  160 . The aperture section  170  is contained in the side wall  144  of the central aperture  138  and extends from the bottom surface  132  of the outboard cutting insert  130  to the point where the mouth  146  joins the side wall  144 . The aperture section  170  has a generally vertical overall orientation in the context of  FIG. 4A . The aperture section  170  has an aperture section bottom surface  171  that is generally arcuate in cross-section. The depth of the aperture section  170  remains generally constant along the length thereof. Although the coolant flow will be described hereinafter, there should be an appreciation that coolant flows in an upward direction (generally parallel to the central longitudinal axis C-C of the central aperture  138 ) (see  FIGS. 5 and 12 ) through a passage defined in part by the aperture section  170  of the primary coolant trough  160 . 
     Still referring to  FIG. 4A , primary coolant trough  160  further has a mouth section  172  of the primary coolant trough  160 . The mouth section  172  is contained in the mouth  146  and extends between the point where the mouth  146  joins the side wall  144  and the point where the mouth  146  joins the rake face  134 . The mouth section  172  is contiguous with the aperture section  170  of the primary coolant trough  160 . The general orientation of the mouth section  172  is at an upward angle relative to the orientation of the aperture section  170 . The mouth section  172  has a mouth section bottom surface  173 . The depth of the mouth section  172  remains generally constant along the length thereof. Although the coolant flow will be described hereinafter, there should be an appreciation that coolant flows from the aperture section  170  into the mouth section  172  wherein the directional orientation of the coolant flow changes to be along the angle of disposition of the mouth section  172  in a radial outward orientation. 
     Referring to  FIGS. 8 and 9 , outboard retention screw  280  has a top end  282  and a bottom end  284  and a threaded portion  286  adjacent to the bottom end  284 . A reduced diameter shank portion  288  is axially forward of the threaded portion  286 . A frusto-conical portion  290  is axially forward of the reduced diameter shank portion  288 , and a head portion  292  is axially forward of the frusto-conical portion  290 . Head portion  292  has a rearward facing surface  294 , a forward facing surface  296  and a peripheral edge  298 . The head portion  292  further contains a screw driver torx reception aperture  300 . 
     Referring to  FIGS. 12 and 13 , keeping in mind the relative orientation between the primary coolant trough  160  and the outboard retention screw  280 , it becomes apparent that the aperture section  170  and the mouth section  172  of the primary coolant trough  160  and at least a portion of the outboard retention screw  280  define there between an outboard primary coolant conduit  302 . More specifically, a portion of the outboard primary coolant conduit  302  is defined between the aperture section  170  and threaded portion  286  of the outboard retention screw  280  and another portion of the outboard primary coolant conduit  302  is defined between the mouth section  172  and the frusto-conical portion  290  of the outboard retention screw  280 . Referring to  FIG. 13A , the coolant is shown by arrows wherein the coolant flows through the outboard primary coolant conduit  302  and through the sections of the primary coolant trough  160  including impinging the outboard retention screw  280 . The flow of the coolant is described in more detail hereinafter. 
     Still referring to  FIG. 4A , primary coolant trough  160  also has a rake face section  174  of the primary coolant trough  160 . The rake section  174  is contained in the rake face  134 . The rake face section  174  extends from the point where the mouth  146  joins the rake face  134  to a point radially inward of the discrete outboard corner  150 . The rake face section  174  is contiguous with the mouth section  172 . The orientation of the rake face section  174  is generally horizontal wherein the rake face section  174  of the primary coolant trough  160  has a depth that decreases in the radial outward direction. The rake face section  174  has a rake face section bottom surface  175 . The depth of the rake face section  174  decreases in the radial outward direction until the rake face section  174  terminates at the exit end  176 . This means that as the rake face section  174  moves in the radial outward direction, the rake section bottom surface  175  moves closer to the rake face  134  until it meets the rake face  134  at the exit end  176 . Although the coolant flow will be described hereinafter, there should be an appreciation that coolant flows from the mouth section  172  into the rake face section  174  wherein the directional orientation of the coolant flow changes to be in a more generally horizontal direction (i.e., generally parallel to the surface of the rake face  134 ) toward the corresponding discrete corner  150 . However, as the coolant flows toward the exit end  176  it moves in an upward direction away from the rake face  134 . 
     The rake face  134  of the outboard cutting insert  130  contains two angular coolant troughs ( 180 ,  200 ) as described hereinafter. As described hereinafter, each angular coolant trough ( 180 ,  200 ) facilitates the delivery of coolant to the vicinity of the interface between the adjacent cutting edges ( 153 ,  157 ) of the outboard cutting insert  130  and the workpiece. 
     More specifically, the rake face  134  of the outboard cutting insert  130  contains a pair of radial innermost angular coolant troughs  180 , each of which has a central longitudinal axis U-U, wherein a radial innermost angular coolant trough  180  is positioned on each side of the rake face section  174  of the primary coolant trough  160 . The radial innermost coolant trough  180  is orientated so the axis U-U is generally perpendicular to the cutting edges. The radial innermost angular coolant troughs  180  are symmetric about a central longitudinal axis A-A (see  FIGS. 4 and 4A ) through the primary outboard coolant trough  160 . Each one of the radial innermost angular coolant troughs  180  has an entrance end  182  and an exit end  184  and an arcuate bottom surface  186 . The entrance end  182  opens directly into the mouth  146  so as to directly receive coolant from the mouth  146 . Coolant then travels along the length of the radial innermost coolant trough  180  exiting via the exit end  184 . Each radial innermost angular coolant trough  180  has a depth that decreases in the radial outward direction, which means that as the arcuate bottom surface  186  moves closer to the rake face  134  until it meets the rake face  134  at the exit end  184 . The decrease in depth in the radial outward direction cause the coolant to exit the radial innermost angular coolant trough  180  in a generally upward orientation moving away from the rake face  134  and toward the vicinity of the outboard cutting insert  130 -chip interface. As shown in  FIG. 4 , this would be in the vicinity of the adjacent cutting edges  151  and  157  adjacent corner  150 . 
     The rake face  134  of the outboard cutting insert  130  further contains a pair of radial outermost angular coolant troughs  200 , each of which has a central longitudinal axis V-V, wherein a radial outermost angular coolant trough  200  is positioned on each side of the rake face section  174  of the primary coolant trough  160 . The radial outermost coolant trough  200  is orientated so the axis V-V is generally perpendicular to the cutting edges. The radial outermost angular coolant troughs  200  are symmetrical about the longitudinal axis A-A of the primary coolant trough  160 . The radial outermost angular coolant trough  200  has an entrance end  202  and an exit end  204  and an arcuate bottom surface  206 . The entrance end  202  opens into the primary coolant trough  160  so as to directly receive coolant from the primary coolant trough  160 . Coolant then travels the length of the radial outermost angular coolant trough  200  exiting via the exit end  204 . The radial outermost angular coolant trough  200  has a depth that decreases in the radial outward direction which means that as the arcuate bottom surface  206  moves closer to the rake face  134  until it meets the rake face  134  at the exit end  204 . The decrease in depth in the radial outward direction cause the coolant to exit the radial outermost angular coolant trough  200  in a generally upward orientation moving away from the rake face  134  and toward the vicinity of the outboard cutting insert  130 -chip interface, which as illustrated in  FIG. 4  is in the vicinity of adjacent cutting edges  151  and  157  adjacent corner  150 . 
     The indexable drill assembly  40  further includes an indexable inboard cutting insert  220 , which exhibits a trigon or trigonal geometry. The inboard cutting insert  220 , as shown in  FIGS. 6 ,  6 A and  7 , has an inboard bottom surface  222  and an inboard rake face  224  as well as inboard flank surfaces  226  that join together the inboard bottom surface  222  and the inboard rake face  224 . The indexable inboard cutting insert  220  contains an inboard central aperture  228  that has a bottom end  230  and a top end  232  and a side wall  234  with a mouth  236 , which has a mouth surface  237 , adjacent to and about the circumference of the top end  232 . The inboard central aperture  228  has a central longitudinal axis E-E. The inboard cutting insert  220  further contains an annular groove  238  about the bottom end  230  of the inboard central aperture  228 . 
     The rake face  224  intersects with the flank surfaces  226  to form three discrete inboard corners ( 240 ,  242 ,  244 ). Inboard cutting insert  220  has three cutting blades (generally designated as  241 ,  243 ,  245 ) wherein each of cutting blades ( 241 ,  243 ,  245 ) is formed by cutting edges ( 246   a - 248   c ). More specifically, cutting blade  241  is formed by cutting edges  246   a  and  248   a , cutting blade  243  is formed by cutting edges  246   b  and  248   b , and cutting blade  245  is formed by cutting edges  246   c  and  248   c . As one skilled in the art can appreciate, the inboard cutting insert  220  can be indexed to different positions to present a different cutting location for engagement with the workpiece. 
     The inboard cutting insert  220  contains three primary coolant troughs  250 ,  252 ,  254  wherein each primary coolant trough corresponds to one of the discrete inboard corners ( 240 ,  242 ,  244 ), respectively. For the sake of brevity, a description of one primary coolant trough  250  will suffice for the description of the other two primary coolant troughs ( 252 ,  254 ) since the three primary coolant troughs ( 250 ,  252 ,  254 ) are substantially identical. 
     Referring to  FIG. 6A , primary coolant trough  250  has an aperture section  256  of the primary coolant trough  250 . The aperture section  256  is contained in the side wall  234  of the central aperture  228  and extends from the bottom surface  222  of the inboard cutting insert  220  to the point where the mouth  236  joins the side wall  234 . The aperture section  256  has a generally vertical orientation in the context of  FIG. 6A . The aperture section  256  has an aperture section bottom surface  251 . The depth of the aperture section  256  remains generally constant along the length thereof. Although the coolant flow will be described hereinafter, there should be an appreciation that coolant flows in an upward direction (generally parallel to a central longitudinal axis D-D (see  FIG. 14 ) of central aperture  228 ) through a passage defined in part by the aperture section  256  of the primary coolant trough  250 . 
     Referring to  FIGS. 10 and 11 , inboard retention screw  306  has a top end  308  and a bottom end  310  and a threaded portion  312  adjacent to the bottom end  310 . A reduced diameter shank portion  314  is axially forward of the threaded portion  312 . A frusto-conical portion  316  is axially forward of the reduced diameter shank portion  314 , and a head portion  318  is axially forward of the frusto-conical portion  316 . Head portion  318  has a rearward facing surface  320 , a forward facing surface  322  and a peripheral edge  324 . The head portion  318  further contains a screw driver torx reception aperture  316 . 
     Referring to  FIGS. 14 and 15 , keeping in mind the relative orientation between the primary coolant trough  250  and the inboard retention screw  306 , it becomes apparent that the aperture section  256  and the mouth section  257  of the primary coolant trough  250  and at least a portion of the inboard retention screw  306  define there between an inboard primary coolant conduit  328 . More specifically, a portion of the inboard primary coolant conduit  328  is defined between the aperture section  256  and threaded portion  312  of the inboard retention screw  306  and another portion of the inboard primary coolant conduit  328  is defined between the mouth section  257  and the frusto-conical portion  316  of the inboard retention screw  306 . Referring to  FIG. 15A , the coolant is shown by arrows wherein the coolant flows through the inboard primary coolant conduit  250  and through the sections of the primary coolant trough  250  including impinging the outboard retention screw  306 . The flow of the coolant is described in more detail hereinafter. 
     Still referring to  FIG. 6A , primary coolant trough  250  further has a mouth section  257  of the primary coolant trough  250 . The mouth section  257  is contained in the mouth  236  and extends between the point where the mouth  236  joins the side wall  234  and the point where the mouth  236  joins the rake face  224 . The mouth section  257  is contiguous with the aperture section  256  of the primary coolant trough  250 . The overall orientation of the mouth section  257  is at an upward angle relative to the orientation of the aperture section  256 . The mouth section  257  has a mouth section bottom surface  253 . The depth of the mouth section  257  remains generally constant along the length thereof. Although the coolant flow will be described hereinafter, there should be an appreciation that coolant flows from the aperture section  256  into the mouth section  257  wherein the directional orientation of the coolant flow changes to be along the angle of disposition of the mouth section  257  and in a radial outward direction. 
     Still referring to  FIG. 6A , primary coolant trough  250  also has a rake face section  258  of the primary coolant trough  250 . The rake face section  258  is contained in the rake face  224 . The rake face section  258  extends from the point where the mouth  236  joins the rake face  224  to a point radially inward of the discrete inboard corner  240 . The rake face section  258  is contiguous with the mouth section  257 . The rake face section  258  has a rake face section bottom surface  255 . The orientation of the rake face section  258  is generally horizontal wherein the rake face section  258  of the primary coolant trough  250  has a depth that decreases in the radial outward direction. The depth of the rake face section  258  decreases in the radial outward direction until the rake face section  258  terminates at the exit end  259 . This means that as the rake face section  258  moves in the radial outward direction, the rake face section bottom surface  255  moves closer to the rake face  224  until it meets the rake face  224  at the exit end  259 . Although the coolant flow will be described hereinafter, there should be an appreciation that coolant flows from the mouth section  257  into the rake face section  258  wherein the directional orientation of the coolant flow changes to be in a generally horizontal direction (i.e., generally parallel to the surface of the rake face  224 ) toward the corresponding discrete inboard corner  240 . However, as the coolant flows toward the exit end  259  it moves in an upward direction away from the rake face  224 . 
     The rake face  224  of the inboard cutting insert  220  contains two angular coolant troughs ( 260 ,  270 ) as described hereinafter. More specifically, the rake face  224  of the inboard cutting insert  220  contains a pair of radial innermost angular coolant troughs  260 , each of which has a central longitudinal axis W-W, wherein a radial innermost angular coolant trough  260  is positioned on each side of the rake face section  258  of the primary coolant trough  250 . The radial innermost coolant trough  260  is orientated so the axis W-W is generally perpendicular to the cutting edges. The radial innermost angular coolant trough  260  has an entrance end  262  and an exit end  264  and an arcuate surface  266 . The entrance end  262  opens directly into the mouth  236  so as to directly receive coolant from the mouth  236 . Coolant then travels along the length of the radial innermost angular coolant trough  260  exiting via the exit end  264 . Each radial innermost angular coolant trough  260  has a depth that decreases in the radial outward direction. The decrease in depth in the radial outward direction causes the coolant to exit the radial innermost angular coolant trough  260  in a generally upward orientation moving away from the rake face  224  and toward the vicinity of the inboard cutting insert  220 -chip interface. As shown in  FIG. 6 , this would be in the vicinity of the adjacent cutting edges  246   a  and  248   c.    
     The rake face  224  of the inboard cutting insert  220  further contains a radial outermost angular coolant trough  270 , which has a central longitudinal axis X-X, positioned on each side of the rake face section  258  of the primary coolant trough  250 . The radial outermost coolant trough  270  is orientated so the axis X-X is generally perpendicular to the cutting edges. The radial outermost angular coolant trough  270  has an entrance end  272  and an exit end  274  and an arcuate surface  276 . The radial outermost angular coolant trough  270  has an entrance end  272  and an exit end  274  and an arcuate bottom surface  276 . The entrance end  272  opens into the primary coolant trough  250  so as to directly receive coolant from the primary coolant trough  250 . Coolant then travels the length of the radial outermost angular coolant trough  270  exiting via the exit end  274 . The radial outermost angular coolant trough  270  has a depth that decreases in the radial outward direction. The decrease in depth in the radial outward direction causes the coolant to exit the radial outermost angular coolant trough  270  in a generally upward orientation moving away from the rake face  224  and toward the vicinity of the inboard cutting insert  220 -chip interface, which is illustrated in  FIG. 6  as adjacent cutting edges  246   a  and  248   c.    
     Coolant is supplied, typically under pressure, to the body coolant channel  54  whereby the coolant flows into each one of the outboard pocket coolant channel  70  and the inboard pocket coolant channel  114 . Coolant enters the outboard pocket body coolant channel  70  via the receiving end  74  and exits through the delivery end  72  into the vicinity of the outboard pocket  58  so as to flow into the outboard cutting insert  130  as described hereinafter. Coolant in the inboard pocket coolant channel  114  enters via the receiving end  118  and exits through the delivery end  116  into the vicinity of the inboard pocket  96  so as to flow into the inboard cutting insert  220  as described hereinafter. 
     In reference to the flow of coolant into the outboard cutting insert  130  and referring to  FIGS. 16 and 17 , the coolant exits the outboard pocket coolant channel  70  through the delivery end  72  into the coolant ring  78  that surrounds the retention screw aperture  76 . The volume defined by the coolant ring  78  and the annular groove  148  in the bottom surface  132  provides an outboard circular coolant conduit  334  for coolant to flow in a generally circular fashion. This generally circular flow pattern is shown in a schematic fashion in  FIG. 16 . Coolant then flows through the outboard circular coolant conduit  334  and into the primary coolant troughs  160 ,  162 ,  164 ,  166  in the outboard cutting insert  130 . Further, the orientation of the primary coolant troughs ( 160 ,  162 ,  164 ,  166 ) can be such so that coolant directly enters the primary coolant troughs ( 160 ,  162 ,  164 ,  166 ). Although the description uses the terminology associated with the primary coolant troughs ( 160 ,  162 ,  164 ,  166 ), there should be an appreciation that the outboard retention screw  280  and each of the primary coolant troughs  160 ,  162 ,  164 ,  166  defines a volume that is a conduit in which coolant flows. 
     Referring to primary coolant trough  160  (which applied to the other primary coolant troughs  162 ,  164 ,  166 ), coolants flows into the primary coolant trough  160  so as to pass through the aperture section  170 . Some of the coolant then impinges on the rearward facing surface  294  of the head portion  292  and is directed to pass through the mouth section  172  and then flow into the rake face section  174  of the primary coolant trough  160 . Further, some of the coolant flows into the entrance end  182  of each one of the radial innermost angular coolant troughs  180  and out of the exit end  184  thereof. Some of the coolant flows into the entrance end  202  of each of the radial outermost angular coolant troughs  200  and out of the exit end  204  thereof. Some of the coolant flows completely through the primary coolant trough  160  exiting at the exit end  176  thereof. As described hereinabove, the coolant exiting the rake face section  174  and the radial innermost angular coolant trough  180  and the radial outermost angular coolant trough  200  travels in a direction generally away from the rake face  134 . 
     The outboard retention screw  280  exerts a so-called “pull back” on the outboard cutting insert  130  so as to pull the outboard cutting insert  130  into the outward pocket  58 . Thus, the volume of coolant entering those primary coolant troughs is greater for the primary coolant troughs farther away from the notch  64  that separates the upstanding walls  60  and  62  as compared to the primary coolant troughs closer to the notch  64 . More specifically, the outboard retention screw  280  provides for a “pull back” feature upon complete tightening into the retention screw aperture  76 . The outboard retention screw  280  accomplishes this feature by a difference in the orientation of the longitudinal axis of the threaded portion  286  as compared to the longitudinal axis of the remainder of the outboard retention screw  280 . This feature is shown and described in issued U.S. Pat. No. 8,454,274 to Chen et al. (assigned to the assignee of the present patent application), which is hereby incorporated by reference herein. This difference in coolant volume flow is shown in  FIG. 17  wherein the longer arrows represent a greater coolant volume. In this regard, one sees that the greatest coolant flow is through primary coolant trough  160 , which is opposite the notch  64 , and the least, if any, coolant flow is through primary coolant trough  164 . Moderate coolant flow is through primary coolant troughs  162  and  166 . This feature allows for more efficient delivery of coolant in that a greater volume of coolant reaches the cutting insert-chip interface (e.g., more coolant is directed to the drill corner point). 
     In reference to the flow of coolant into the inboard cutting insert  220  and referring to  FIGS. 18 and 19 , the coolant exits the inboard pocket coolant channel  114  through the delivery end  116  into the coolant ring  122  that surrounds the retention screw aperture  120 . The volume defined by the coolant ring  122  and the annular groove  238  in the bottom surface  222  provides an inboard circular coolant conduit  340  for coolant to flow in a generally circular fashion. This generally circular flow pattern is shown in a schematic fashion in  FIG. 18 . Coolant then flows through the inboard circular coolant conduit  340  and into the primary coolant troughs  250 ,  252 ,  254  in the inboard cutting insert  220 . Further, the orientation of the primary coolant troughs ( 250 ,  252 ,  254 ) can be such that coolant directly enters the primary coolant troughs ( 250 ,  252 ,  254 ). Although the description uses the terminology associated with the primary coolant troughs ( 250 ,  252 ,  254 ), there should be an appreciation that the outboard retention screw  306  and each of the primary coolant troughs ( 250 ,  252 ,  254 ) defines a volume (or conduit) through which coolant flows. 
     Referring to primary coolant trough  250  (which applied to the other primary coolant troughs  252 ,  254 ), coolant flows into the primary coolant trough  250  so as to pass through the aperture section  256 . Some of the coolant then impinges on the rearward facing surface  320  of the head portion  318  of the inboard retention screw  306  and is directed to pass through the mouth section  257  and then flow into the rake face surface section  258  of the primary coolant trough  250 . Coolant flows out of the rake face section  258  at the exit end  259 . Further, some of the coolant flows into the entrance end  262  of each one of the radial innermost angular coolant troughs  260  and out of the exit end  264  thereof. Some of the coolant flows into the entrance end  272  of each of the radial outermost angular coolant troughs  270  and out of the exit end  274  thereof. Some of the coolant flows completely through the primary coolant trough  250  exiting at the exit end  259  thereof. As described hereinabove, the coolant exiting the rake face section  258  and the radial innermost angular coolant trough  260  and the radial outermost angular coolant trough  270  travels in an upward direction away from the rake face  224 . 
     The inboard retention screw  306  exerts a so-called “pull back” on the inboard cutting insert  220  so as to pull the inboard cutting insert  220  into the inboard pocket  96 . Thus, the volume of coolant entering the primary coolant troughs is greater for the primary coolant troughs farther away from the central notch  104  that separates the upstanding walls  102  and  106 . More specifically, the inboard retention screw  306  provides for a “pull back” feature upon complete tightening into the retention screw aperture  120 . The outboard retention screw  306  accomplishes this feature by a difference in the orientation of the longitudinal axis of the threaded portion  312  as compared to the longitudinal axis of the remainder of the inboard retention screw  306 . This feature is shown and described in issued U.S. Pat. No. 8,454,274 to Chen et al. (assigned to the assignee of the present patent application) which is hereby incorporated by reference herein. This difference in coolant volume flow is shown in  FIG. 19  wherein the longer arrows represent a greater coolant volume. In this regard, one sees that the greater coolant flow is through primary coolant troughs  250  and  254 , and the least, if any, coolant flow is through primary coolant trough  252 . This feature allows for more efficient delivery of coolant in that a greater volume of coolant reaches the cutting insert-chip interface (e.g., more coolant is directed to the drill corner point). 
     Referring to  FIGS. 20 through 22 , there is shown another specific embodiment of an indexable cutting insert generally designated as  344 , which exhibits a generally rectangular geometry. The indexable cutting insert  344  has a bottom surface  346  and a rake face  348  as well as flank surfaces  350  that join together the bottom surface  346  and the rake face  348 . The indexable cutting insert  344  contains a central aperture  352  that has a bottom end  354  and a top end  356  and a side wall  358  with a mouth  360 , which has a mouth surface  361 , adjacent to and about the circumference of the top end  356 . The indexable cutting insert  344  further contains an annular groove  362  about the bottom end  354  of the central aperture  352 . The rake face  348  intersects with the flank surfaces  350  to form four discrete corners ( 364 ,  366 ,  368 ,  370 ), as well as four discrete cutting edges ( 372 ,  374 ,  376 ,  378 ) of the indexable cutting insert  344 . Each cutting edge ( 372 ,  374 ,  376 ,  378 ) is defined between adjacent corners ( 364 ,  366 ,  368 ,  370 ). For example, cutting edge  372  is defined between corners  364  and  366 . As one skilled in the art can appreciate, the indexable cutting insert  344  can be indexed to different positions to present a different selected one of the cutting edges ( 372 ,  374 ,  376 ,  378 ) for engagement with the workpiece. 
     The indexable cutting insert  344  contains four primary coolant troughs ( 380 ,  382 ,  384  and  386 ) wherein each primary coolant trough ( 380 ,  382 ,  384  and  386 ) corresponds to one of the discrete corners ( 364 ,  366 ,  368 ,  370 ), respectively. For the sake of brevity, a description of one primary coolant trough  380  will suffice for the description of the other three primary coolant troughs ( 382 ,  384 ,  386 ) since the four primary coolant troughs ( 380 ,  382 ,  384  and  386 ) are substantially identical. Primary coolant trough  380  has a central longitudinal axis Z-Z. 
     Referring to  FIG. 20A , primary coolant trough  380  has an aperture section  388  of the primary coolant trough  380 . The aperture section  388  is contained in the side wall  358  of the central aperture  352  and extends from the bottom surface  346  of the indexable cutting insert  344  to the point where the mouth  360  joins the side wall  358 . The aperture section  388  has a generally vertical orientation in the context of  FIG. 20A . The aperture section  388  has an aperture section bottom surface  389 . The depth of the aperture section  388  remains generally constant along the length thereof. Although the coolant flow will be described hereinafter, there should be an appreciation that coolant flows in an upward direction (generally parallel to the central longitudinal axis P-P of the central aperture  352 ) through a passage defined in part by the aperture section  388  of the primary coolant trough  380 . 
     Still referring to  FIG. 20A , primary coolant trough  380  has a mouth section  390  of the primary coolant trough  380 . The mouth section  390  is contained in the mouth  360  and extends between the point where the mouth  360  joins the side wall  358  and the point where the mouth  360  joins the rake face  348 . The mouth section  390  is contiguous with the aperture section  388  of the primary coolant trough  380 . The orientation of the mouth section  390  is at an upward angle relative to the orientation of the aperture section  388 . The mouth section  388  has a mouth section bottom surface  391 . The depth of the mouth section  390  remains generally constant along the length thereof. Although the coolant flow will be described hereinafter, there should be an appreciation that coolant flows from the aperture section  388  into the mouth section  390  wherein the directional orientation of the coolant flow changes to be generally along the angle of disposition of the mouth section  390  in a radial outward orientation. 
     Still referring to  FIG. 20A , primary coolant trough  380  has a rake face section  392  of the primary coolant trough  380 . The rake face section  392  is contained in the rake face  348 . The rake face section  392  extends from the point where the mouth  360  joins the rake face  348  to a point radially inward of the discrete corner  364 . The rake face section  392  is contiguous with the mouth section  390 . The rake face section  392  has a rake face section bottom surface  393 . The orientation of the rake face section  392  is generally horizontal wherein the rake face section  392  of the primary coolant trough  380  has a depth that decreases in the radial outward direction. Although the coolant flow will be described hereinafter, there should be an appreciation that coolant flows from the mouth section  390  into the rake face section  392  wherein the directional orientation of the coolant flow changes to be in a more generally horizontal direction (i.e., generally parallel to the surface of the rake face  348 ) toward the corresponding discrete corner  364 . However, as the coolant flows toward the exit end  394  it moves in an upward direction away from the rake face  348 . 
     The rake face  348  of the indexable cutting insert  344  contains angular coolant troughs  396  as described hereinafter. Each angular radial coolant trough  396 , which has a central longitudinal axis Y-Y, facilitates the delivery of coolant to the vicinity of the interface between the adjacent cutting edges ( 374 ,  376 ) of the indexable cutting insert  344  and the workpiece. The angular coolant trough  396  is orientated so the axis Y-Y is generally perpendicular to the cutting edges. 
     More specifically, the rake face  348  of the indexable cutting insert  344  contains a pair of angular coolant troughs  396  positioned on each side of the rake face section  174  of the primary coolant trough  382 . The angular coolant trough  396  is symmetric about a central longitudinal axis Z-Z through the primary coolant trough  382 . The angular coolant troughs  396  each have an entrance end  398  and an exit end  400  and an arcuate surface  402 . The entrance end  398  opens into the mouth  360  so as to receive coolant from the mouth  360 . Coolant then travels along the length of the angular coolant trough  396  exiting via the exit end  400 . The angular coolant trough  396  has a depth that decreases in the radial outward direction. The decrease in depth in the radial outward direction cause the coolant to exit the angular coolant trough  396  in a generally upward orientation moving away from the rake face  348  and toward the vicinity of the indexable cutting insert  344 -chip interface, which is in the vicinity of the cutting edges  372 ,  378 . The coolant exiting the rake face section  392  and the radial angular coolant trough  396  travels in an upward direction away from the rake face  348 . 
     The present invention provides an indexable drill useful for the drilling of holes in a workpiece adapted to facilitate enhanced delivery of coolant adjacent the interface between the workpiece and each one of the outboard cutting insert and the inboard cutting insert (insert-chip interface) so as to diminish excessive heat at the insert-chip interface in a hole drilling operation. By diminishing the heat, the present invention is able to reduce excessive heat at the insert-chip interface to eliminate or reduce build up of chip material. By diminishing the heat, the present invention will facilitate the evacuation of chips from the insert-chip interface thereby minimizing the potential that a chip will be re-cut during the drilling operation. 
     The patents and other documents identified herein are hereby incorporated by reference herein. Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or a practice of the invention disclosed herein. It is intended that the specification and examples are illustrative only and are not intended to be limiting on the scope of the invention. The true scope and spirit of the invention is indicated by the following claims.