Patent Publication Number: US-9890635-B2

Title: Tapered cutter bit and mounting block for the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation of application Ser. No. 14/262,918 filed Apr. 28, 2014, which is a continuation-in-part of application Ser. No. 14/136,063 filed Dec. 20, 2013. 
    
    
     BACKGROUND 
     This invention generally relates to the field of rotary driven cylindrical scarifiers for use in roadway surface milling. More particularly, the present invention is directed to wear resistant inserts on abrasive cutting elements for such rotary driven cylindrical scarifiers that can be used on equipment for modifying the surface of an existing road, and in particular, to equipment for smoothing areas of existing pavement by removing bumps, upward projections, and other surface irregularities, removing paint stripes, and milling shallow recessed to receive roadway edging and marking tape. 
     In general, roadway surface milling, planing, mining or reclaiming equipment disclosed in the prior art includes a rotary driven cylindrical comminuting drum which acts to scarify or mine the top portion of the asphaltic road surface in situ. Road planning machines are used to remove bumps and other irregularities on the surface of a road, runway, taxiway, or other stretch of pavement. This planning effect is typically achieved by grinding the paved surface so that the grinding depth may vary slightly, but the surface produced by the grinding unit is more level than the original surface. The road planning machine typically includes a grinding unit that is powered by an engine or motor. A tractor is attached to, or integral with, the grinding unit for propelling the grinding unit against the paved surface in a desired direction. 
     In some prior art devices of this type, a plurality of cutter bit support members are connected by bolts or by a weld to the curved surface of a drum or to flighting fixed to a drum surface. The plurality of the support members can be arranged end-to-end so as to form a more or less continuous helical pattern. The top surface of the helically arranged support members may be elevated above the curved surface of the drum. The top surfaces of the cutter bit support members can include angled openings into which conventional cutter bits are received. The cutter bits can be a conical cutter with preferably a tungsten carbide tip or the like. The tip can have a variety of shapes. 
     Examples of a cutter bit holder and drum are disclosed in U.S. Pat. Nos. 4,480,873; 5,052,757; 7,108,212; 7,290,726; and 7,338,134 to Latham where a rotatable drum has a generally cylindrical outer surface, and a plurality of blocks are mounted onto the outer surface of the drum. The blocks can be positioned onto the drum relative to one another such that the blocks define a helical flight extending around the outer surface of the drum, or can be spaced from each other in any desired pattern. Each of the blocks includes a first side wall, a second side wall, and a top surface. The first and second side walls are generally parallel to one another and generally perpendicular to the drum. The top surfaces of the blocks can define an outer periphery of the flight, if so arranged. Each of the blocks includes a slot and at least one pocket formed therein. The slot is generally rectangular and adapted to receive a tool holder. The slot includes first and second slot side walls, a bottom surface and a rear slot wall. The first and second slot side walls are generally parallel to one another and generally perpendicular to the rear slot wall. The rear slot wall can be oriented at an angle relative to the first and second side walls of the block. A generally rectangular shaped tool or tool holder is received within the slot of each block. 
     Each block also includes at least one pocket on one of the side walls of the slot. The pocket is generally circular and includes a generally cylindrically shaped retainer positioned therein. Each retainer includes a planar tapered surface that is parallel to and engages one side of the rectangular body of the tool or tool holder within the slot of the block to secure the tool holder in the slot. Each block includes a first hole extending from the second side wall to the rear slot wall. The first hole is oriented generally perpendicular to the rear slot wall. A threaded fastener extends through the hole and engages a threaded bore formed within the tool holder to further secure the tool holder within the slot of the block. Each pocket of each block includes a second hole extending from the pocket to the second side wall that can be oriented generally perpendicular to the second side wall. A threaded fastener can extend through the hole and engage a threaded bore formed within the retainer to pull the retainer within the pocket along a longitudinal axis of the second hole such that the planar tapered surface of the retainer pushes the tool holder against the rear slot wall and the side slot wall to keep the tool holder secured within the slot. This arrangement allows for easy quick replacement of the tool holder when the cutting element or tool held by the tool holder becomes worn or damaged. 
     More recently, it has been suggested that the cutting surfaces of the cutting tools used in the previously described blocks be formed of a diamond composition such as that disclosed in U.S. Pat. No. 8,501,144 to Bertagnolli. The diamond cutting surfaces can comprise diamond, polycrystalline diamond, natural diamond, synthetic diamond, vapor deposited diamond, silicon bonded diamond, cobalt bonded diamond, thermally stable diamond, infiltrated diamond, layered diamond, cubic boron nitride, diamond impregnated matrix, diamond impregnated carbide, metal catalyzed diamond, or combinations thereof. The diamond cutting surfaces thus formed exhibit extremely long life under the very abrasive environments encountered in roadway surface milling, planing, or reclaiming. The abrasive wear is such that the tool held by the tool holder can degrade from contact with the passing drift to such a point as to require replacement of the tool even though the cutting surface is still performing satisfactorily. 
     Thus, there exists a need in the art for an apparatus having a cutter bit insert for a milling drum, with or without flighting, that is capable of removable attachment to a drum and is resistant to wear, particularly when the cutting element is an extremely long-lasting diamond cutting surface. There is also a need for a cutter bit that can be quickly removed from the drum and replaced so that the down time experience during cutter bit replacement is minimized. 
     SUMMARY 
     A cutter bit of the present design can be used with a mounting block that can be adapted to be fixed onto a cutting drum for a scarifying milling machine. The cutter bit can take the form of an elongated body having an upper end including a cutting surface. An upper portion of the elongated body can be generally rectangular, or cylindrical, or other suitable shape. The cutter bit can have a lower end that can be shaped as shown in my earlier patents, for example, U.S. Pat. Nos. 4,480,873; 5.052.757; 7,108,212; and 7,338,134. A lower end of the cutter bit can also have a front surface having an optional lower planar tapered portion, and a back surface obverse to the front surface. The back surface can be planar over at least that portion obverse to the lower planar tapered portion. The cutter bit can include a wear resistant element replaceably mounted to the front surface of the elongated body immediately below the cutting surface. In one embodiment, the elongated body can comprise a hardened steel, while the cutting surface can comprise a diamond composition that can be fixed in a step adjacent the upper end of the elongated body. The cutting surface can comprise diamond, polycrystalline diamond, natural diamond, synthetic diamond, vapor deposited diamond, silicon bonded diamond, cobalt bonded diamond, thermally stable diamond, infiltrated diamond, layered diamond, cubic boron nitride, diamond impregnated matrix, diamond impregnated carbide, metal catalyzed diamond, or combinations thereof. The wear resistant element can comprise a carbide composition or a sintered diamond composition. The wear resistant element can have a variety of shapes and angular attitudes to deflect the passing drift away from the cutter bit body. The wear resistant element can be, for example, round, square, rectangular, trapezoidal or other shape, including an irregular shape that is best suited to the cutter bit elongated body or any inclination to which the cutter bit elongated body might be mounted in a mounting block. 
     In one embodiment, the cutter bit can include an opening through the elongated body immediately below the cutting surface from the front surface to the back surface of the elongated body. A stem can be received in the opening, the stem having a front end and a back end. The wear resistant element can be fixed to the front end of the stem. The wear resistant element can be replaced, when needed, by at least partially removing the stem from the opening and inserting a new stem having a new wear resistant element on the front end of the new stem. A fastener can be removably coupled to the back end of the stem to secure the stem in the opening. The opening receiving the stem can be perpendicular to the back surface of the elongated body. The elongated body can include an angled notch including a surface inclined with respect to the back surface of the stem. The opening receiving the stem can be perpendicular to the inclined surface of the angled notch. 
     In one embodiment, the cutter bit can include an opening through the elongated body immediately below the cutting surface from the front surface to the back surface of the elongated body. A stem can be received in the opening, the stem having a front end and a back end. A wear resistant element can be fixed to a nut that can be secured to the front end of the stem. The wear resistant element can be replaced, when needed, by loosening the stem from the combined nut and wear resistant element, substituting a new combined nut and wear resistant element, and re-tightening the stem into the new combined nut and wear resistant element. 
     In one embodiment, the mounting block can have a first side wall, a second side wall, and a top surface. The first and second side walls can be generally parallel to one another and generally perpendicular to the top surface. A slot can be positioned within a first side wall and extend through the top surface. The slot can be generally rectangular and include first and second slot side walls, a bottom surface and a rear slot wall. The first and second slot side walls can be generally parallel to one another and generally perpendicular to the rear slot wall so as to define a generally rectangular slot. The rear slot wall can be oriented at an angle relative to the first and second side walls of the mounting block so that the generally rectangular slot is at an angle. At least one pocket can situated within one of the first and second side walls to intercept the slot, and a retainer can be positioned within each pocket. Each retainer can include a planar laterally tapered surface designed to interact with a surface of the cutter bit elongated body, which can be dimensioned to be removably mounted within the slot. Optionally, the at least one pocket can be inclined with respect to the first and second side walls. 
     In one embodiment, the optional lower tapered portion of the cutter bit can include a pair of vertically spaced tapered portions, each tapered portion contacting the planar laterally tapered surface of one of the retainers. The rectangular elongated body portion of the cutter bit can also include an opening laterally aligned with respect to the cutting surface and adapted to receive a fastener coupling the elongated body portion to the slot back wall. 
     In one embodiment, the cutter bit lower portion can take a form similar to that shown in U.S. Pat. No. 7,300,115 to Holl et al. An upper portion can take the form of a generally rectangular elongated body having an upper end including a cutting surface. The cutter bit can also have a front surface and a back surface obverse to the front surface. The cutter bit can include a wear resistant element replaceably mounted to the front surface immediately below the cutting surface. The cutter bit body can comprise a hardened steel, the diamond cutting surface can be fixed in a step in the upper end of the cutter bit body, and the wear resistant element can comprise a carbide composition or a sintered diamond composition. The wear resistant element can have a variety of shapes and angular attitudes to deflect the passing drift away from the cutter bit body. 
     In one embodiment the cutting surface can have side edges that taper laterally outwardly toward the lower edge of the cutting surface that is adjacent to the wear resistant element. The laterally outwardly tapering edges of the cutting surface can assist in protecting the cutter bit body from wear caused by the passing drift. In one embodiment, the upper edge of the wear resistant element can be formed to closely conform to the shape of the adjacent lower edge of the cutting surface to inhibit wear of the cutter bit body between the cutting surface and the wear resistant element. 
     One feature of the apparatus is that the wear resistant element can be replaceably mounted to the front surface of the cutter bit immediately below the cutting surface. The feature has the advantage of permitting serial replacement of the wear resistant element without requiring that the cutter bit be removed for the mounting block holding the cutter bit, thereby lowering hardware replacement time and providing extended life for the cutter bit. Alternatively, in some circumstances, the wear resistant element can merely be rotated to a new orientation relative to the cutter bit thereby lowering hardware replacement costs. 
     Another feature of the apparatus is that the wear resistant elements can be provided with a variety of shapes and angular attitudes. This feature has the advantage of not merely resisting but also deflecting the passing drift away from the cutter bit body, thereby extending the life of the cutter bit body. 
     Another feature of the apparatus is that the mounting blocks can be secured to the cutter drum surface in a variety of patterns to define virtually any lacing pattern. The mounting blocks can be secured to the cutter drum in spaced relation to each other, or immediately adjacent to each other so as to define a flighting. 
     These and other features and their corresponding advantages of the disclosed combination will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a mounting block holding a cutter bit having a replaceable wear resistant insert. 
         FIG. 2  is a perspective view taken with a top section removed along line  2 - 2  of  FIG. 1 . 
         FIG. 3  is a perspective view of another cutter bit having a replaceable wear resistant insert. 
         FIG. 4  is vertical sectional view of the cutter bit shown in  FIG. 1 . 
         FIG. 5  is a perspective view of a replaceable wear resistant insert having an inclined front face. 
         FIG. 6  is a perspective view of a replaceable wear resistant insert having a dual inclined front face. 
         FIG. 7  is a perspective view of a replaceable wear resistant insert formed as a nut to be secured to cutter bit mounting block by a separate fastener. 
         FIG. 8  is a perspective view of another cutter bit having a replaceable wear resistant insert. 
         FIG. 9  is a perspective view of another cutter bit having a replaceable wear resistant insert and a cutting surface having laterally outwardly tapering side edges. 
         FIG. 10  is a sectional view, somewhat similar to  FIG. 4 , of an upper portion of another cutter bit including an angled notch having a surface inclined with respect to the back surface of the stem. 
         FIG. 11  is a perspective view of an upper portion of another cutter bit where the upper edge of the wear resistant element is formed to closely conform to the shape of the adjacent lower edge of the cutting surface. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to all the drawings, the same reference numerals are generally used to identify like components.  FIG. 1  is a perspective view of a mounting block  10  holding a cutter bit  12  having a replaceable wear resistant element  14 . The mounting block  10  can have a first side wall  16 , a second side wall  18 , and a top surface  20 . The first and second side walls  16 ,  18  can be generally parallel to one another, as shown in  FIG. 2 . The first and second side walls  16 ,  18  can be generally perpendicular to the top surface  20 . A slot  22  can be positioned within the first side wall  16  and extend through the top surface  20 . The slot  22  can be generally rectangular and include a first slot sidewall  24  and a second slot side wall  26 , and a rear slot wall  28 . The first and second slot side walls  24 ,  26  can be generally parallel to one another and generally perpendicular to the rear slot wall  28  so as to define a generally rectangular slot. The rear slot wall  28  can be parallel to or oriented at any angle relative to the first and second side walls  16 ,  18  of the mounting block  10  so that the generally rectangular slot  22  can be situated at any angle. At least one pocket  30  can situated within the first side wall  16  to intercept the slot  22 . The least one pocket  30  can alternatively be situated within the second side wall  18  to intercept the slot  22 . A retainer  32  can be positioned within each pocket  30 . Each retainer  32  can include a planar laterally tapered surface  34  designed to interact with a surface  36  of the elongated body of the cutter bit  12 . Each retainer  32  can include an opening  31  adapted to receive a suitable fastener  33  extending inward from the second side wall  18 . The mounting block  10  can have a lower surface  38  having curvature suitable for mating with the surface of a rotatable drum or other working surface of a roadway surface milling, planing, or reclaiming machine or other equipment in a variety of patterns and alignments. The lower surface  38  can include a perimeter  40  adapted for welding attachment to the rotatable drum or other working surface. 
     In the embodiment of the cutter bit  12  shown in  FIGS. 1-4 , the cutter bit has a generally rectangular body  42  dimensioned to be removably mounted within the slot  22 . The cutter bit can also have an upper end  44  including a cutting surface  46  situated contiguous to the upper end  44 . The cutting surface  46  can be formed of a diamond composition and can have a variety of shapes. The diamond composition can be diamond, polycrystalline diamond, natural diamond, synthetic diamond, vapor deposited diamond, silicon bonded diamond, cobalt bonded diamond, thermally stable diamond, infiltrated diamond, layered diamond, cubic boron nitride, diamond impregnated matrix, diamond impregnated carbide, metal catalyzed diamond, or combinations thereof. The cutter bit  12  can also have a lower end  48 , and a front surface  50 . The front surface  50  can optionally have a lower planar tapered portion  56  that can be engaged by the laterally tapered surface  34  of each retainer  32  to secure the cutter bit  12  within the slot  22 . A wear resistant element  14  can be replaceably mounted to the front surface  50  immediately below the cutting surface  46  and above the top surface  20  of the mounting block  10 . The cutter bit  12  can have lateral tapered surfaces  52  extending from the upper end  44  down to the rectangular body  42 . The wear resistant element  14  can be received in a slot  54  in the front surface  50 , and can extend substantially entirely between the lateral tapered surfaces  52 . The wear resistant element  14  can have a variety of shapes and angular attitudes to deflect the passing drift away from the cutter bit body. The vertical extent and shape of the wear resistant element  14  can be adapted as needed to protect the front surface  50  of the cutter bit  12  from excessive wear by contact with the abrasive drift removed from the surface being milled, preferably to a preferred side of the cutter bit  12 . 
     As seen in  FIGS. 2 and 3 , the front surface  50  of the cutter bit  12  can include a pair of vertically spaced tapered portions  56 , each tapered portion being dimensioned to be contacted by the planar laterally tapered surface  34  of one of the retainers  32 . While  FIG. 2  shows the retainer  32  being pulled by fastener  33  into the contacting relationship with the tapered portion  56 , the tapered portions  56  of the cutter bit  12  can be omitted. Where the front surface  50  has no tapered portions  56 , the pocket  30  and the opening for the fastener  33  can be inclined with respect to the front surface  50  of the cutter bit, so that the laterally tapered surface  34  of the retainer  32  contacts the front surface  50 . The rectangular elongated body portion  42  of the cutter bit can also include an opening  58  laterally aligned with respect to the cutting surface  46  and adapted to receive a fastener  60  extending inward from the second sidewall  18  to couple the elongated body portion  42  to the slot rear wall  28 . In the event that the cutter bit  12  as a whole needs replaced, the fasteners  33  can be removed from the openings  31  in each retainer  32 . The fastener  60  can be removed from opening  58  and the cutting bit  12  laterally removed from the holding block  10 . The cutter bit  12  and the holding block  10  can have a variety of shapes and sizes, and can be mounted to a working surface of a variety of roadway surface milling, planing, mining or reclaiming machines and equipment in a variety of patterns and alignments. 
     As seen in  FIGS. 1, 3, and 4 , the cutting surface  46  can have a variety of shapes and sizes. In a preferred embodiment the cutting surface  46  comprises a diamond composition fixed in a step  62  in the upper end  44  of the cutter bit  12 . The elongated body  42  of the cutter bit is typically formed of a hardened steel, while the wear resistant element  14  preferably comprises a carbide composition that significantly resists wear from the passing abrasive drift removed from the surface being milled. As seen if  FIG. 3 , both the cutting surface  46  and the surface of the wear resistant element  14  can be recessed from the front surface  50  of the cutter bit  12  by a further step  64   
       FIG. 4  is a vertical sectional view of the cutter bit  12  shown in  FIG. 1 , but is representative of a preferred mounting for the wear resistant element  14 . The cutter bit  12  can include an opening  66  through the elongated body  42  immediately below the cutting surface  46  from the front surface  50  to the back surface  68  of the elongated body. A stem  70  having a front end  72  and a back end  74  can be received in the opening  66 . The wear resistant element  14  can be fixed to the front end  72  of the stem  70 . A fastener  76  can be removably coupled to the back end  74  of the stem  70  to secure the stem in the opening  66 . The stem  70  can include a tapered portion  73  which can act to ensure the proper positioning of the wear resistant element  14 . Depending on the configuration of the front surface  13  of the wear resistant element, the wear resistant element may be rotated from time to time to lengthen the life of the wear resistant element  14 . The wear resistant element  14  can be replaced, when needed, by removing the fastener  76  from the stem  70 , and forcing the stem  70  from the opening  66 , typically by a moderate tap from a hammer or the like. A new stem  70  having a new wear resistant element  14  on the front end  72  can then be inserted in the opening  66  and secured in place by fastener  76 . This arrangement permits serial replacement of the wear resistant element  14  without requiring that the cutter bit  12  be removed for the mounting block  10  holding the cutter bit, thereby lowering hardware replacement time and providing extended life for the cutter bit  12 . 
       FIGS. 5-7  show some examples of variations in wear resistant elements  14  that can be formed to be coupled to any of the cutter bits  12  illustrated herein, as well as other non-illustrated cutter bits, so as to protect the front surface  50  of the cutter bit  12  from excessive wear by contact with the abrasive drift removed from the surface being milled. As shown in  FIG. 5 , the front end  72  of the stem  70  can be inclined with respect to a surface perpendicular to the stem  70 . The wear resistant element  14  can be fixed to the front end  72  of the stem  70  so that the front surface  13  of the wear resistant element is also inclined with respect to the stem  70 . The wear resistant element  14  shown in  FIG. 5  can be inserted into an opening  66  of any cutter bit  12  so that the front surface  13  is inclined to either side of the cutter bit, or upward or downward so as to deflect the passing drift away from the cutter bit body, thereby extending the life of the cutter bit body. 
     The front end  72  of the stem  70  can also be doubly inclined with respect to a surface perpendicular to the stem  70  as shown in  FIG. 6 . Wear resistant elements  14  can be fixed to the front end  72  of the stem  70  so that the front surfaces 13  of the wear resistant elements are also inclined with respect to the stem  70 . The wear resistant elements  14  shown in  FIG. 6  can be inserted into an opening  66  of any cutter bit  12  so that the front surfaces  13  are inclined to deflect the passing drift to both sides of the cutter bit body, thereby extending the life of the cutter bit body. While  FIGS. 6 and 7  have shown two particularly useful shapes and angular attitudes for the wear resistant elements  14 , other useful shapes will be apparent to those skilled in the art. 
       FIG. 7  shows an alternate arrangement for a wear resistant element  14  wherein the wear resistant element  14  can be fixed to a nut  80  having a treaded interior surface  82  that can be secured to a bolt or other threaded fastener that can be inserted into the opening  66  from the back surface  68  of the elongated body shown in  FIG. 4 . The back surface  81  of the nut  80  can include a tapered portion  83  to help center and lock the nut  80  within the step  62  below the diamond cutting surface  46 . The combined nut  80  and wear resistant element  14  can be rotated an necessary to preserve the life of the wear resistant element  14 . The wear resistant element  14  can be replaced, when needed, by loosening the bolt from the combined nut  80  and wear resistant element  14 , substituting a new combined nut  80  and wear resistant element  14 , and re-tightening the bolt into the new combined nut and wear resistant element. The front surface  13  of the combined nut  80  and wear resistant element  14  can have a variety of useful shapes and angular attitudes, including those useful shapes and angular attitudes shown in  FIGS. 5 and 6 . 
       FIG. 8  shows another cutter bit  12  having a replaceable wear resistant insert  14 . A lower portion  84  of the cutter bit  12  can take a form similar to that shown in U.S. Pat. No. 7,300,115 to Holl et al., including a stem  86  designed to be received into a suitable mounting block, not shown. The stem  86  can include spaced tapered portions  85 ,  87  on a forward surface of the stem, and a clamping face  88  on a rearward surface of the stem, which act to ensure alignment of the cutter  12  in a desired direction with respect to the mounting block in which the stem  86  is received. A plate  90  can be provided at an upper end of the stem  86 . An upper portion  91  can be fixed to an upper surface of the plate  90 , and can take the form of a generally elongated body  42  having an upper end  44  including a cutting surface  46 . The stem  86  including the spaced tapered portions  85 ,  87  can be directed to ensure a desired rake angle of the diamond cutting surface  46  and to ensure the top surface  44  is parallel to the center line of the drum forming the working surface. The cutter bit upper portion  91  can also have a front surface  50  and a back surface  68  obverse to the front surface  50 . The cutter bit upper portion  91  can include a wear resistant element  14  replaceably mounted to the front surface  50  immediately below the cutting surface  46 . The cutter bit body  42 , stem  86 , and plate  90  can comprise a hardened steel. The cutting surface  46  can comprise a diamond composition which can be fixed in a step  62  adjacent the upper end  44  of the cutter bit body  42 . The wear resistant element  14  can comprise a carbide composition or a sintered diamond composition. The wear resistant element  14  can have a variety of shapes and angular attitudes, including those illustrated in  FIGS. 1, 3, and 4-8 , to deflect the passing drift away from the cutter bit body  42 . The wear resistant element  14  can additionally have a variety of other shapes including, for example, round, square, rectangular, trapezoidal or other shape, including an irregular shape that is best suited to the shape of the cutter bit elongated body  42  or any inclination to which the cutter bit elongated body might be mounted in a mounting block. 
     In the embodiment of the cutter bit  12  shown in  FIG. 9 , the cutter bit has a generally rectangular body  42 . The cutter bit  12  can also have an upper end  44  including a cutting surface  46  situated contiguous to the upper end  44 . The cutting surface  46  can be formed of a diamond composition and can have side edges  45  and  47  that taper laterally outwardly toward a lower edge  49  adjacent to the wear resistant element  14 . The laterally outwardly tapering edges  45  and  47  of the cutting surface  46  can assist in protecting the cutter bit  12  from wear caused by passing drift. The diamond composition forming the cutting surface  46  can be diamond, polycrystalline diamond, natural diamond, synthetic diamond, vapor deposited diamond, silicon bonded diamond, cobalt bonded diamond, thermally stable diamond, infiltrated diamond, layered diamond, cubic boron nitride, diamond impregnated matrix, diamond impregnated carbide, metal catalyzed diamond, or combinations thereof. The cutter bit  12  can also have a lower end  48  that can be configured variously such as shown in  FIG. 3  or  FIG. 8 . The cutter bit  12  can have a front surface  50 . A wear resistant element  14  can be replaceably mounted to the front surface  50  immediately below the lower edge  49  of the cutting surface  46 . The cutter bit  12  can have lateral tapered surfaces  52  extending from the upper end  44  down to the rectangular body  42 . The wear resistant element  14  can be received in a slot  54  in the front surface  50 , and can extend substantially entirely between the lateral tapered surfaces  52 . The wear resistant element  14  can have a variety of shapes and angular attitudes to deflect the passing drift away from the cutter bit body as shown, for example, in  FIGS. 5 and 6 . The vertical extent and shape of the wear resistant element  14  can be adapted as needed to protect the front surface  50  of the cutter bit  12  from excessive wear by contact with the abrasive drift removed from the surface being milled, preferably to a preferred side of the cutter bit  12 . 
       FIG. 10  is a vertical sectional view of another cutter bit  12  showing another preferred mounting for the wear resistant element  14 . The cutter bit  12  can include an opening  66  through the elongated body  42  immediately below the cutting surface  46  from the front surface  50  to the back surface  68  of the elongated body  42 . The back surface  68 , which can be generally parallel to the front surface  50  can include an angled notch  67  including a surface  69  inclined with respect to the back surface  68  of the body  42 . The opening  66  can be perpendicular to the back surface  68  of the body  42  as shown in  FIG. 4 . Alternatively, the opening  66  can be perpendicular to the inclined surface  69  of the angled notch  67 . A stem  70  having a front end  72  and a back end  74  can be received in the opening  66 . The wear resistant element  14  can be fixed to the front end  72  of the stem  70 . A fastener  76  can be removably coupled to the back end  74  of the stem  70  to secure the stem in the opening  66 . The stem  70  can include a tapered portion  73  which can act to ensure the proper positioning of the wear resistant element  14 . Depending on the configuration of the front surface  13  of the wear resistant element, the wear resistant element may be rotated from time to time to lengthen the life of the wear resistant element  14 . The wear resistant element  14  can be replaced, when needed, by removing the fastener  76  from the stem  70 , and forcing the stem  70  from the opening  66 , typically by a moderate tap from a hammer or the like. A new stem  70  having a new wear resistant element  14  on the front end  72  can then be inserted in the opening  66  and secured in place by fastener  76 . This arrangement permits serial replacement of the wear resistant element  14  without requiring that the cutter bit  12  be removed for the mounting block  10  holding the cutter bit, thereby lowering hardware replacement time and providing extended life for the cutter bit  12   
     In the embodiment of the cutter bit  12  shown in  FIG. 11 , the cutter bit can have an upper end  44  including a cutting surface  46  situated contiguous to the upper end  44 . The cutting surface  46  can be formed of a diamond composition and can have a variety of shapes. A wear resistant element  14  can be replaceably mounted to the front surface  50  immediately below the cutting surface  46 . The vertical and horizontal extent and shape of the wear resistant element  14  can be adapted as needed to protect the front surface  50  of the cutter bit  12  from excessive wear by contact with the abrasive drift removed from the surface being milled. The wear resistant element  14  can have an upper edge  13  that is formed to closely conform to the shape of the adjacent lower edge  49  of the cutting surface  46 , can be received in a slot  54  in the front surface  50 , and can extend substantially entirely between the lateral tapered surfaces  52 . The wear resistant element  14  can have a variety of angular attitudes to deflect the passing drift away from the cutter bit body. 
     The foregoing detailed description should be regarded as illustrative rather than limiting, and the following claims, including all equivalents, are intended to define the spirit and scope of this invention