Patent Publication Number: US-10323515-B1

Title: Tool with steel sleeve member

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims priority to and is a continuation-in-part of U.S. Non-provisional application Ser. No. 15/261,277, filed Sep. 9, 2016, and U.S. Non-provisional application Ser. No. 15/261,277 claims priority to U.S. Provisional Application No. 62/237,070, filed Oct. 5, 2015; this application claims priority to and is a continuation-in-part of U.S. Non-provisional application Ser. No. 14/719,638, filed May 22, 2015, U.S. Non-provisional application Ser. No. 14/719,638 claims priority to and is a continuation-in-part of U.S. Non-provisional application Ser. No. 13/801,012, filed Mar. 13, 2013, now U.S. Pat. No. 9,039,099, issued May 26, 2015, and U.S. Non-provisional application Ser. No. 13/801,012 claims priority to U.S. Provisional Application No. 61/716,243, filed Oct. 19, 2012; this application claims priority to and is a continuation-in-part of U.S. Non-provisional application Ser. No. 14/714,547, filed May 18, 2015, U.S. Non-provisional application Ser. No. 14/714,547 claims priority to and is a division of U.S. Non-Provisional application Ser. No. 13/801,012, filed Mar. 13, 2013, now U.S. Pat. No. 9,039,099, issued May 26, 2015, and U.S. Non-provisional application Ser. No. 13/801,012 claims priority to U.S. Provisional Application No. 61/716,243, filed Oct. 19, 2012; this application claims priority to and is a continuation-in-part of U.S. Non-provisional application Ser. No. 14/487,493, filed Sep. 16, 2014, and U.S. Non-provisional application Ser. No. 14/487,493 claims priority to U.S. Provisional Application 61/879,353, filed Sep. 18, 2013; this application claims priority to and is a continuation-in-part to U.S. Non-provisional application Ser. No. 15/220,569, filed Jul. 27, 2016; this application claims priority to and is a continuation-in-part to U.S. Non-provisional application Ser. No. 15/220,595, filed Jul. 27, 2016; and this application claims priority to and is a continuation-in-part to U.S. Non-provisional application Ser. No. 15/220,607, filed Jul. 27, 2016, to the extent allowed by law and the contents of which are incorporated herein by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to a steel sleeve member for bit assemblies used in road milling, mining, and trenching equipment. 
     BACKGROUND 
     Originally, road milling equipment was used to smooth out bumps on the surface of a roadway or to grind down the joinder of two adjacent concrete slabs that may have buckled. Now, these road milling machines are also used for completely degrading concrete and macadam roads down to their gravel base. Additionally, the road milling equipment can be used for trenching and mining operations. The combinations of bit assemblies have been utilized for a wide variety of operations, such as to remove material from the terra firma, such as degrading the surface of the earth, minerals, cement, concrete, macadam or asphalt pavement. 
     Road milling, mining, and trenching equipment are operated using a rotatable, cylindrical drum that includes a plurality of bit holder blocks mounted onto the drum in a herringbone, V-shape, or spiral configuration. Bits are traditionally set in a bit assembly having a bit holder that is retained within a bore of the bit holder block. Bits can include an insert having a conical cutting tip that is mounted in a recess in a frustoconical forward body portion of the bit. The insert can be made of a hardened material and/or can be surrounded by a hardened annular collar that provides added wear resistance to the cutting tool. The insert is further protected by a metal or steel sleeve. The cutting tool can include a solid generally cylindrical shank that extends axially rearwardly from the forward body portion. The bit fits in a central bore of the bit holder. As described, these bit holders are frictionally seated in the bores of their respective bit holder blocks mounted on the drums. These bit holders are not held in the bores of their respective bit holder blocks by retaining clips or threaded nuts, thereby providing easier removal and replacement once the bit holders are worn through use or broken due to the harsh road degrading environment. 
     Historically, these bits and bit holders have been made of steel with hardened metal or tungsten carbide tips or collars to lengthen the useful service life of the bit holder. Heavy duty road milling, mining, and trenching operations, however, impose much more wear and tear than the currently used industry standard bit holders can handle. The forces and vibrations exerted on the bit assemblies from the harsh road degrading environment may cause the bit holder to move within the bore of the bit holder block. Individual bits may wear or be broken off of their shanks because of the harsh environment and may also lead to the need to replace the bit holder. 
     Recently, materials harder than tungsten carbide, such as polycrystalline diamond or the like, have been used in certain road milling operations, notably the degradation of asphalt layers on long roadway stretches. While the hardness of the polycrystalline diamond tip lengthens the useful life of the combined bit and bit holder, the polycrystalline diamond tip of the combination is so brittle that it is generally not suitable for use in degrading concrete highways or curved highway stretches, such as cloverleafs and the like. 
     To prolong the life of the polycrystalline diamond tip bit assembly and prevent damage to the bit assemblies in heavy duty operations, a heavy duty combination bit and bit holder is provided that is sturdy enough to withstand the forces found when degrading or breaking up the surfaces of not only macadam (asphalt) roadways but also concrete roadways. Additionally, the metal sleeve supports both transverse and angular loads on the vertically exposed portion of the insert, which shields the forward end of the insert. The addition of this metal sleeve offers support and allows greater extension of the insert from the forward end. Most importantly, the metal sleeve significantly speeds the heat transfer in the induction brazing process and limits the polycrystalline diamond from excessive heat buildup which reduces degradation. The heat generated when the polycrystalline diamond is removing macadam, for example, dissipates faster through the metal sleeve, which will significantly increase the useful service life, by at least double, of a polycrystalline diamond insert brazed atop of a tungsten carbide bolster. 
     SUMMARY 
     This disclosure relates generally to bit assemblies for road milling, mining, and in particular trenching equipment. One implementation of the teachings herein is a bit holder for road milling machinery that includes a substantially solid body having an upper end and a lower end, the upper end being diametrically smaller than the lower end; a generally cylindrical hollow shank depending axially from the lower end, the shank having a bore axially extending from a distal end of the shank toward the forward body portion; and a steel annular sleeve disposed circumferentially around the upper end of the body, the sleeve configured to receive a bit. 
     These and other aspects of the present disclosure are disclosed in the following detailed description of the embodiments, the appended claims and the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features, advantages, and other uses of the apparatus will become more apparent by referring to the following detailed description and drawings, wherein like reference numerals refer to like parts throughout the several views. It is emphasized that, according to common practice, the various features of the drawings are not to-scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. 
         FIG. 1  is a detail side elevation view of a first embodiment of a bit assembly showing a bit or insert, a bit holder, and a bit holder block; 
         FIG. 2  is a detail exploded side elevation view of the first embodiment of the bit assembly, showing the assembled bit or insert and bit holder apart from the bit holder block; 
         FIG. 3  is a detail exploded side elevation view of the first embodiment of the bit holder, without the bit, showing a bit holder body, a carbide collar, a carbide insert, and a metal sleeve; 
         FIG. 4  is a detail side elevation view of the first embodiment of the bit holder, without the bit, assembled with the carbide collar, carbide insert, and metal sleeve; 
         FIG. 5  is a detail exploded side elevation view of the first embodiment of the bit holder, showing a first braze disc, a metal cup, a second braze disk, and the bit or insert; 
         FIG. 6  is a detail side elevation view of a second embodiment of a bit assembly showing a bit or insert, with a frustoconical forward end, attached to a bit holder and a bit or insert with a flat generally cylindrical puck forward end; and 
         FIG. 7  is a detail exploded side elevation view of the second embodiment of the bit holder, showing an annular carbide collar and a metal sleeve and the bit or insert, with either a frustoconical forward end or a flat generally cylindrical puck forward end. 
     
    
    
     DETAILED DESCRIPTION 
     Road milling, mining, and trenching equipment are operated using a rotatable, cylindrical drum that includes a plurality of bit holder blocks mounted onto the drum in a herringbone, V-shape, or spiral configuration. Bits are traditionally set in a bit assembly having a bit holder that is retained within the bit holder block. The bit is retained by the bit holder and a shank of the bit holder is retained within a bore in the bit holder block. Bits can include an insert having a conical cutting tip that is mounted in a recess in a frustoconical forward body portion of the bit. The insert can be made of a hardened material and/or can be surrounded by a hardened annular collar that provides added wear resistance to the cutting tool. The insert is further protected by a metal or steel sleeve. The cutting tool can include a solid generally cylindrical shank that extends axially rearwardly from the forward body portion. The bit fits in a central bore of the bit holder. As described, these bit holders are frictionally seated in the bores of their respective bit holder blocks mounted on the drums, thereby providing easier removal and replacement once the bit holders are worn through use or broken due to the harsh road degrading environment. 
     The combinations of bit assemblies have been utilized to remove material from the terra firma, such as degrading the surface of the earth, minerals, cement, concrete, macadam or asphalt pavement. Individual bits, bit holders, and bit holder blocks may wear down or break over time due to the harsh road trenching environment. Bit holder blocks, herein after referred to as base blocks, are generally made of steel. Tungsten carbide and diamond or polycrystalline diamond coatings, which are much harder than steel, have been used to prolong the useful life of bits and bit holders. However, while polycrystalline diamond layers and coatings have a hardness that lengthens the useful life of the combined bit and bit holder, the polycrystalline diamond tip of the combination is so brittle that it is not economically suitable for use in degrading concrete highways or curved highway stretches. 
     To prolong the life of the polycrystalline diamond tip bit assembly and prevent damage to the bit assemblies in heavy duty operations, a heavy duty combination bit and bit holder is provided that is sturdy enough to withstand the forces found when degrading or breaking up the surfaces of not only macadam (asphalt) roadways but also concrete roadways. One important aspect of the present disclosure is that the metal sleeve supports both transverse and angular loads on the vertically exposed portion of the insert, which shields the forward end of the insert. The addition of this metal sleeve offers support and allows greater extension of the insert from the forward end. Another important aspect of the present disclosure is that the metal sleeve significantly speeds the heat transfer in the induction brazing process and limits the polycrystalline diamond from excessive heat buildup, which reduces degradation. The heat generated when the polycrystalline diamond is removing macadam, for example, dissipates faster through the metal sleeve, which significantly increases the useful service life, by at least double, of a polycrystalline diamond insert brazed atop of a tungsten carbide bolster. 
     Referring to  FIGS. 1-5 , a first embodiment of a bit assembly  10  ( FIG. 1 ), or diamond tool, comprises a bit or insert  12  ( FIGS. 1, 2, and 5 ), a bit holder  14 , and a base block  16  ( FIGS. 1 and 2 ). The combination bit and bit holder of the present disclosure is a unitary bit and bit holder construction that includes a bit holder body  18  and a generally cylindrical hollow shank  20  axially depending from the bottom of the bit holder body  18 . In this embodiment, the bit holder body  18  is generally annular in shape and comprises an enlarged upper body  22  having a cylindrical base  24 , termed in the trade as a tire portion, and a cylindrical side wall extending upwardly from the tire portion  24  to the upper body  22 . The upper body  22  of the bit holder body  18 , in this embodiment, is a generally convex surfaced solid structure. In other embodiments, the enlarged upper body  22  can have various shapes, such as having a generally frustoconical, concave, or arcuate surfaced solid structure. In this embodiment, the enlarged upper body  22  includes an aperture  26  that accepts a sleeve to facilitate the insertion of the bit holder  14  to the base block  16 . 
     The bit holder body  18  of the bit/bit holder combination provides added bulk and strength to the entire unitary assembly which allows the bit/bit holder combination of the present disclosure to withstand substantial forces and stress superior to heretofore known bit holders or bit/bit holder combinations. The present disclosure may be utilized not only in the degrading and removal of macadam or asphalt from long straight stretches of roadway, but may also provide for the removal of concrete and other materials both in straight long stretches and in curved sections such as at corners, cloverleaf intersections, or the like. 
     The shank  20  includes a central bore  28  that longitudinally and axially extends throughout the shank  20  of the bit holder body  18  of the bit/bit holder combination. The central bore  28  terminates, in this embodiment, at bore termination  30  that is approximately at an upper end  32 , shown in  FIGS. 2-5 , of the shank  20 . A sidewall  34  (not shown) of the shank  20 , created by the central bore  28 , further includes an elongated slot  36  extending from a generally annular distal end  38  of the shank  20  axially upward or forward to an upper termination  40  (not shown) that is adjacent to the forward or upper end  32  of the shank  20 . This allows the generally C-shaped annular sidewall  34  (not shown) of the shank  20  to radially contract when the shank  20  is mounted in one of a positively tapered, cylindrical, or negatively tapered base block bore  42 , shown in  FIGS. 1 and 2 , in the base block  16 . 
     The shank  20  includes a lower or first tapered portion  44  running axially from a stepped shoulder  46  adjacent the distal end  38  of the shank  20 . The first tapered portion  44  runs upwardly or axially from the stepped shoulder  46  of the shank  20  and terminates generally mid slot  36  longitudinally. The shank  20  also includes a second tapered portion  48  separating the first tapered portion  44  from an upper or third tapered portion  50  which extends from the second tapered portion  48  a generally cylindrical upper or fourth portion  52  of the shank  20 , as shown in  FIGS. 2-5 . The generally cylindrical fourth portion  52  extends from the third tapered portion  50  towards a generally annular back flange  54 , shown in  FIGS. 2-5 , that denotes the base of the bit holder body  18  of the bit holder  14 . In other embodiments, the fourth portion  52  can also be positively or negatively tapered. 
     The generally annular flange  54  includes a pair of tapered cutouts  56  ( FIGS. 1-5 ),  58  (not shown), or wedge-shaped undercuts, to provide access and leverage for a tool to extract the bit holder  14  from the base block  16 . The tapered cutouts  56 ,  58  are formed into the tire portion  24  and extend from the flange  54  subjacent to the tire portion  24 . The tapered cutouts  56 ,  58  include a pair of parallel flat vertical inner surfaces  60  ( FIGS. 1 and 4 ),  62  (not shown), respectively, and a pair of flat tapered top surfaces  64  ( FIGS. 1 and 4 ),  66  (not shown), respectively. The outer edge of the flat tapered top surfaces  64 ,  66  is each arcuate in shape to follow the periphery of the tire portion  24 . 
     The upper body  22  of the bit holder body  18  includes a generally annular top surface  68  positioned perpendicular to the axis of the bit holder  14  from the interior of which axially extends a smaller radially oriented annular tapered upper or forward extension  70 . A forwardly extending annular collar  72  is created on the bit holder body  18  to provide an annular trough  74  around the tapered upper extension  70  of the bit holder body  18 , as shown in  FIG. 3 . An annular carbide collar  76  is fitted around the tapered upper extension  70 , which may be brazed into unitary construction with the remainder of the bit holder  14 . A top or forwardmost portion of the carbide collar  76  and the annular tapered upper extension  70  of the upper body  22  terminate generally at the top of the bit holder body  18  of the combination bit/bit holder. 
     With the bit holder body  18  of the present disclosure preferably made of  4340  or equivalent steel, the top of the upper extension  70  of the upper body  22  includes a generally cylindrical or radially declining tapered bore  78  extending from the co-terminal upper wall of the body axially inwardly thereof which defines, in this illustrated embodiment, a declining radial taper. The tapered bore  78  extends a short distance longitudinally axially inwardly of the annular upper extension  70  that defines the base for the carbide collar  76 . Bore  78  can also have a hollow cylindrical shape or a slight draw or draft angle. 
     The generally cylindrical or declining tapered bore  78  provides a space for receiving a complementary shaped positive generally cylindrical or declining tapered outer surface of a solid carbide insert  80  for the bit/bit holder combination. The carbide insert  80  for the bit also extends upwardly and is tapered outwardly axially longitudinally from the co-terminal upper extension  70  of the bit holder body  18  and includes an upper annular ring portion  82 , shown in  FIGS. 3 and 4 , and a generally cylindrical bore  84 , shown in  FIGS. 3-5 , positioned centrally and extending inwardly from the upper annular ring portion  82 . In other embodiments, the carbide insert  80  can extend upwardly and be generally cylindrical or have a slight draft angle. An annular steel sleeve  86  is fitted around the outwardly extending portion of the carbide insert  80 , which may be brazed into unitary construction with the remainder of the bit holder  14 , as shown in  FIG. 4 . 
     The annular steel sleeve  86  supports transverse and/or angular loads on the vertically exposed portion of the carbide insert  80  that is positioned beyond a forward end  77 , shown in  FIGS. 3 and 4 , of the carbide collar  76 . The annular steel sleeve  86  also shields and protects the forward end, that extends past the carbide collar  76 , of the carbide insert  80  where the generally cylindrical bore  84  is located because a thin carbide wall  85  of the carbide insert  80 , created by the bore  84  of the carbide insert  80 , will fracture and break apart when subject to even minor impacts. The addition of the annular steel sleeve  86  allows for greater extension of the carbide insert  80  from the forward end of the carbide collar  76  than permitted by previous designs. 
     A receiving cup  88 , shown in  FIG. 5 , is mounted in the generally cylindrical bore  84  of the carbide insert  80 . In this embodiment, the receiving cup  88  is made of steel and may have a thin bottom portion  90  and a hollow cup forward portion  92  into which a tip base  94 , shown in  FIGS. 1, 2, and 5 , of a bit tip  12  may be positioned and brazed therein to provide a unitary structure. In other embodiments, the receiving cup  88  can be about ⅜-1 inch in height and include a thick bottom portion and a hollow cup forward portion. The reasoning behind the addition of the receiving cup  88  relates to the bond between the carbide to steel to carbide sequence, which yields substantially stronger bonds than brazing tungsten carbide to tungsten carbide alone. 
     The tip base  94  may be made of steel or tungsten carbide and includes a tip at the outer or upper end of the bit tip. In this embodiment, the outer surface or upper end  96 , shown in  FIGS. 1, 2, and 5 , of tip  12  is made of a polycrystalline diamond structure. The tip  12  can have a frustoconical shape, a flat generally cylindrical puck shape ( FIGS. 1, 2, and 5 ), or an arcuate shape. The upper end  96  of the bit tip  12  may also be made of an industrial diamond material and may be a coating or outer layer of such industrial diamond material, natural diamond, or polycrystalline diamond (PCD) material. The coating or layer may be formed of a high pressure, high temperature process. 
     The flat generally cylindrical puck shaped upper end  96  of the bit  12  of the bit holder  14 , shown in  FIGS. 1, 2, and 5 , provides a substantially stronger tip that is able to withstand the added forces and peak jolts found in degrading concrete and the like, and together with the added bulk of the bit holder body  18  of the illustrated bit/bit holder combination in  FIGS. 1-5 , is capable of removing or degrading concrete surfaces with the added life expectancy shown in prior bit/bit holder constructions with PCD tips that have heretofore been utilized only in removing long straight stretches of macadam. The receiving cup  88  holding the puck-shaped tip  12  is also an impact absorbing member that can stretch and compress without fracturing. A road milling machine can travel faster with forward speed using the instant bit/bit holders than it can with bit holders having a strictly tungsten carbide forward end. 
     The bit assembly  10  is assembled using a two-step brazing process. Parts of the bit assembly  10 , such as, for example, the annular trough  74 , bore  78 , carbide collar  76 , carbide insert  80 , steel sleeve  86 , receiving cup  88 , and tip  12 , that are to be brazed together are first treated through a fluxing process. The parts are fluxed to clean, promote melting, and protect the parts from oxidation. In preparation for the brazing process, as shown in  FIG. 3 , a brazing ring  97  is positioned and mounted in the annular trough  74  of the bit holder body  18 , the carbide collar  76  is positioned and mounted into the annular trough  74  such that the bottom portion  79  of the carbide collar  76  rests on the brazing ring  97 , two brazing rings  93 ,  95  are positioned and located in the bottom of bore  78  of the forward extension  70  and around the carbide insert  80  that is inserted through the carbide collar  76  and is positioned and mounted into the bore  78  of the upper body  22 , a brazing ring  99  is positioned around the forward end  77  of the carbide ring  76 , and the steel sleeve  86  is positioned and mounted around the carbide insert  80  such that the bottom portion  87  of the steel sleeve  86  rests on the brazing ring  99 . In this brazing process, the bit holder  14  assembly is brazed as an assembly in a one step process, shown in  FIG. 4 . The liquidus of the brazing rings  93 ,  95 ,  97 ,  99  material is at a brazing temperature of approximately 1900 degrees Fahrenheit (F). Once the bit holder  14  has cooled, the bit holder  14  is heat treated for hardening and tempering. 
     In preparation for this brazing process, a brazing disc  98  ( FIG. 5 ) is positioned and mounted in the bore  84  of the carbide insert  80 , the receiving cup  88  is positioned and mounted in the bore  84  of the carbide insert  80  such that the bottom portion  90  rests on the brazing disc  98 , another brazing disc  100  ( FIG. 5 ) is then positioned and mounted in the hollow cup forward portion  92  of the receiving cup  88 , and the hardened tip  12  is then positioned and mounted in the hollow cup forward portion  92  of the receiving cup  88  such that the base  94  of the tip  12  rests on the brazing disc  100 , as shown in  FIG. 5 . The fully assembled tool is then ready for the second brazing process. In this brazing process, the receiving cup  88  and hardened tip  12  are brazed in a one step process using the brazing discs  98 ,  100  positioned as shown in  FIG. 5 . The receiving cup  88  provides a carbide-steel-carbide sandwich that, when brazed together, is stronger than the combination of brazing the tungsten carbide insert directly to the tungsten carbide substrate of the hardened tip. 
     The annular steel sleeve  86  significantly speeds the heat transfer in the induction brazing process and limits the PCD insert or bit  12  from excessive heat buildup that causes degradation of cobalt to diamond and diamond to diamond bonds. The maximum temperature of the PCD insert or bit  12 , which is brazed at the forward end of the carbide insert  80 , is 1300 degrees F. in an open atmosphere brazing process. The liquidus of the brazing discs  98 ,  100  material is 1260 degrees F., which attach the PCD insert or bit  12  to the forward end of the carbide insert  80 . The liquidus of the brazing discs  98 ,  100  material is much lower, 1260 degrees F., than the liquidus of the brazing rings  97 ,  99  material ( FIG. 3 ), which are brazed at 1700 degrees F. Each brazing disc and brazing ring suitably sized to fit the dimensions of the bit holder. 
     The annular steel sleeve  86  not only extends the useful life of the diamond tool throughout the manufacturing process by eliminating scrap due to mishandling, but also extends the useful life of the diamond tool in removing macadam from road surfaces. The heat generated, when the PCD insert or bit  12  of bit assembly  10  is removing macadam, dissipates faster through the annular steel sleeve  86 . Steel materials transfer heat approximately five times faster than tungsten carbide. In using the annular steel sleeve  86  to shield the carbide insert  80 , the service life of the bit assembly  10  is increases the useful life of a PCD insert brazed atop a tungsten carbide bolster alone. 
     Referring to  FIGS. 6 and 7 , a second embodiment of a bit assembly  110  (not shown), or diamond tool, comprises a bit or insert  112 , a bit holder  114 , and a base block  116  (not shown). The combination bit and bit holder of the present disclosure is a unitary bit and bit holder construction that includes a bit holder body  118  and a generally cylindrical hollow shank  120  ( FIGS. 6, 7 ) axially depending from the bottom of the bit holder body  118 . In this embodiment, the bit holder body  118  is generally annular in shape and comprises an enlarged upper body  122  having a tire portion  124  and a cylindrical side wall extending upwardly from the tire portion  124  to the upper body  122 . The upper body  122  of the bit holder body  118 , in this embodiment, is a generally convex surfaced solid structure. In other embodiments, the enlarged upper body  122  can have various shapes, such as having a generally frustoconical, concave, or arcuate surfaced solid structure. In this embodiment, the enlarged upper body  122  includes an aperture  126  that accepts an insertion sleeve to facilitate inserting the bit holder  114  into the base block  116 . 
     The bit holder body  118  of the bit/bit holder combination provides added bulk and strength to the entire unitary assembly which allows the bit/bit holder combination of the present disclosure to withstand substantial forces and stress superior to heretofore known bit holders or bit/bit holder combinations. The present disclosure may be utilized not only in the degrading and removal of macadam or asphalt from long straight stretches of roadway, but may also provide for the removal of concrete and other materials both in straight long stretches and in curved sections such as at corners, cloverleaf intersections, or the like. 
     The shank  120  includes a central bore  128  (not shown) that longitudinally and axially extends throughout the shank  120  of the bit holder body  118  of the bit/bit holder combination. The central bore  128  terminates, in this embodiment, at bore termination  130  (not shown) that is approximately at a generally cylindrical forward portion  132  of the shank  120 . A sidewall  134  (not shown) of the shank  120 , created by the central bore  128 , further includes an elongated slot  136  (not shown) extending from a generally annular distal end  138  of the shank  120  axially upward or forward to an upper termination  140  (not shown) that is adjacent to the upper or forward portion  132  of the shank  120 . This allows the generally C-shaped annular sidewall  134  of the shank  120  to radially contract when the shank  120  is mounted in one of a positively tapered, cylindrical, or negatively tapered base block bore  142  (not shown) in the base block  116 . 
     The shank  120  includes a lower or first tapered portion  144  running axially from a stepped shoulder  146  adjacent the distal end  138  of the shank  120 . The first tapered portion  144  runs upwardly or axially from the stepped shoulder  146  of the shank  120  and terminates generally mid slot  136  (not shown) longitudinally. The shank  120  also includes a second tapered portion  148  separating the first tapered portion  144  from an upper or third tapered portion  150  which extends from the second tapered portion  148  to the generally cylindrical forward portion  132  of the shank  120 . The generally cylindrical forward portion  132  extends from the third tapered portion  150  towards a generally annular back flange  154  that denotes the base of the bit holder body  118  of the bit holder  114 . In other embodiments, the forward portion  132  can also be positively or negatively tapered. 
     The generally annular flange  154  includes a pair of tapered cutouts  156  ( FIGS. 6 and 7 ),  158  (not shown), or wedge-shaped undercuts, to provide access and leverage for a tool to extract the bit holder  114  from the base block  116  (not shown). The tapered cutouts  156 ,  158  are formed into the tire portion  124  and extend from the flange  154  subjacent to the tire portion  124 . The tapered cutouts  156 ,  158  include a pair of parallel flat vertical inner surfaces  160  ( FIGS. 6 and 7 ),  162  (not shown), respectively, and a pair of flat tapered top surfaces  164  ( FIGS. 6 and 7 ),  166  (not shown), respectively. The outer edge of the flat tapered top surfaces  164 ,  166  is each arcuate in shape to follow the periphery of the tire portion  124 . 
     The upper body  122  of the bit holder body  118  includes a generally annular top surface  168  positioned perpendicular to the axis of the bit holder  114  from the interior of which axially extends a smaller radially oriented annular tapered upper or forward extension  170 . A forwardly extending annular collar  172  is created on the bit holder body  118  to provide an annular trough  173  ( FIG. 7 ) around the tapered upper extension  170  of the bit holder body  118 , as shown in  FIG. 7 . An annular carbide collar  175  is fitted around the tapered upper extension  170 , which may be brazed into unitary construction with the remainder of the bit holder  114 . A top or forwardmost portion of the carbide collar  175  and the annular tapered upper extension  170  of the upper body  122  terminate generally at the top of the bit holder body  118  of the combination bit/bit holder. 
     With the bit holder body  118  of the present disclosure preferably made of  4340  or equivalent steel, the top of the upper extension  170  of the upper body  122  includes a cylindrical bore  177  extending from the co-terminal upper wall of the body axially inwardly thereof. The bore  177  extends a short distance longitudinally axially inwardly of the annular upper extension  170  that defines the base for the tip base  174  of the bit tip  112 , which may be positioned and brazed therein to provide a unitary structure. In other embodiments, the upper extension  170  can include a radially declining tapered bore, a generally cylindrical bore, or a bore with a slight draw or draft angle. 
     The tip base  174  may be made of steel or tungsten carbide and includes a tip at the outer or upper end of the bit tip. In this embodiment, the outer surface or upper end  176  of tip  112  is made of a polycrystalline diamond structure. The upper end  176  of the tip  112  can have a frustoconical shape  178 , a flat generally cylindrical puck shape  180 , or an arcuate shape (not shown). The upper end  176  of the bit tip  112  may also be made of an industrial diamond material and may be a coating or outer layer of such industrial diamond material, natural diamond, or polycrystalline diamond (PCD) material. The coating or layer may be formed of a high pressure, high temperature process. 
     The flat generally cylindrical puck shape  180  upper end  176  of the bit  112  of the bit holder  114 , shown in  FIGS. 6 and 7 , provides a substantially stronger tip that is able to withstand the added forces and peak jolts found in degrading concrete and the like, and together with the added bulk of the bit holder body  118  of the illustrated bit/bit holder combination, is capable of removing or degrading concrete surfaces with the added life expectancy shown in prior bit/bit holder constructions with PCD tips that have heretofore been utilized only in removing long straight stretches of macadam. A road milling machine can travel faster with forward speed using the instant bit/bit holders than it can with bit holders having a strictly tungsten carbide forward end. 
     The bit holder  114  is assembled using a two-step brazing process. As previously described with regard to the first embodiment, parts of the bit holder  114  that are to be brazed together are first treated through a fluxing process. The parts are fluxed to clean, promote melting, and protect the parts from oxidation. In preparation for the brazing process, as shown in  FIG. 7 , a brazing ring  181  is positioned and mounted in the annular trough  173  of the bit holder body  118  and the carbide collar  175  is positioned and mounted into the annular trough  173  such that a bottom portion  179  ( FIG. 7 ) of the carbide collar  175  rests on the brazing ring  181 . The carbide collar  175  is brazed to the bit holder body  118  by melting brazing ring  181  and then the combination bit holder body  118  and the carbide collar  175  is heat treated. After the bit holder has been heat treated, a brazing disc  182  is positioned and mounted in the bore  177  of the forward extension  170  and the hardened tip  112  is then positioned and mounted in the bore  177  of the forward extension  170  such that the base  174  of the tip  112  rests on the brazing disc  182 . The braze material of brazing disc  182  has a lower melting point than the braze material used in brazing ring  181 . The lower liquidus temperature of approximately 300 degrees F. of brazing disc  182  ensures that brazing ring  181  will not melt when the base  174  of the tip  112  is brazed to the forward extension  170  of the bit holder  114 , by melting brazing ring  182  to approximately 1300 degrees F. The fully assembled tool is then ready for the brazing process where the tip  112  is brazed directly into the forward extension  170  of the steel upper body  122  of the bit holder  114 . 
     While the present disclosure has been described in connection with certain embodiments, it is to be understood that the invention is not to be limited to the disclosed embodiments but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is permitted under the law.