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BACKGROUND 
     This invention generally relates to the field of rotary driven cylindrical cutter devices and scarifiers for use in roadway surface milling. More particularly, the present invention is directed to tooth and retainer inserts for such rotary driven cylindrical cutter devices and 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, or reclaiming equipment disclosed in the prior art includes a rotary driven cylindrical comminuting drum which acts to scarify and to 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. 
     One example of a cutter bit holder and drum is disclosed in U.S. Pat. No. 5,884,979 to Latham. Here, the drum surface omits any flighting, but includes a plurality of spaced recesses arranged in a preselected pattern, each recess being defined by a generally circular upper edge and including a bottom surface depressed below the driven member rotatable surface. Each cutting bit holding element has a body portion having at least one aperture receiving the cutting bit and a lower portion having a generally cylindrical outer surface sized to be received in only one of said recesses. The lower portion has a reference lower end abutting the recess bottom surface with a locating element engaging the cutting bit holder element lower end with a niche within said recess for orienting the cutting bit holder with respect to said cutting direction. When the cutting bit holding elements are situated within the recesses, they are secured in position by means of a weld line joining the cutting bit holding element to the surface of the drum in a line outside of the upper edge of each recess. In the event of wear or catastrophic failure of one or more of the cutting bit holding elements, the worn or failed element must be removed from the assembly. Replacement of the holding element requires the use of a cutting torch, and the welding of a new support member in place. This is a time-consuming repair job which results in considerable expense to a mining machine operation, and results in a decreased rate in mining. 
     Despite the availability of such devices, there exists a need in the art for an apparatus having a cutter bit insert for a milling drum, preferably without flighting, that is capable of removable attachment to the drum, yet is resistant to loosening upon rotation of the milling drum. There is also a need for a cutter bit a cutter bit having low profile above the drum so that the total diameter of the drum including cutter bits is less than about 18 inches. 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 combination can be used on any selected portion of a milling or planning drum that preferably omits any flighting and is adapted to be rotated in a cutting direction about an axis defined by the cylindrical surface of the drum. The combination includes a plurality of pairs of overlapping recesses in the cylindrical surface of the drum. The combination can also include a tooth or cutting bit having a base configuration matching a first of the pair of the overlapping recesses, and a lower portion of a side surface including a retainer engagement feature. The combination can also include a retainer having a base configuration matching a second of the pair of overlapping recesses, and a side surface including a tooth engagement feature. A fastener can secure the retainer in the second of the pair of overlapping recesses so that the tooth engagement feature of the retainer engages the retainer engagement feature of the tooth or cutting bit. 
     The combination can include a drum wherein each of the pairs of overlapping recesses includes side surfaces that are parallel to each other. In a preferred embodiment, each of the pairs of overlapping recesses can be aligned along a circumference line extending around the cylindrical surface of the drum. The combination can also include a retainer engagement feature on the lower portion of a side surface of the tooth which comprises an inclined planar surface facing outwardly relative to the drum cylindrical surface. The combination can also include a tooth engagement feature on the retainer which comprises an inclined planar surface facing inwardly relative to the drum cylindrical surface. In a preferred embodiment, the inclined planar surface on the side surface of the tooth is angled to be abutted by the inclined planar surface of the retainer to lock the tooth into the first of the overlapping recesses in the drum. 
     The combination can also include a retainer wherein the fastener comprises a screw passing through the retainer so that the fastener is engaged into a threaded opening in the base of the second of the pair of overlapping recesses. In a preferred embodiment, the retainer includes a hole passing through the retainer in alignment with the threaded opening in the base of the second of the pair of overlapping recesses, the hole having a diameter greater than the threaded opening in the base, the hole having an internal engagement feature. The internal engagement feature of the hole in the retainer can be design to engage an extraction tool. The extraction tool can take the form of a slide hammer including a shaft and a slide weight, the shaft having an end adapted to engage the engagement feature of the hole in the retainer to pull the retainer and tooth from the overlapping recesses. Alternatively, the extraction tool can take the form of a threaded extraction screw having a diameter greater than the fastener diameter that engages the engagement feature of the hole in the retainer, so that an end of the extraction screw abuts a surface within the second of the pair of overlapping recesses to push the retainer and tooth from the overlapping recesses. 
     One feature of the apparatus is that the retainer can be sized to have an upper surface that is situated below the cylindrical surface of the drum when the retainer and tooth are fully engaged in the overlapping recesses. The feature has the advantage of substantially eliminating any wear on the sides of the retainer so that the retainer can be used repeatedly with new teeth or cutting bits, thereby lowering hardware replacement costs. 
     Another feature of the apparatus is that the upper end of the cutting bit or tooth can have any desired configuration, including a broad flat chisel point particularly suitable for roadway surface milling and planing equipment intended 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. A particular advantage of this combination is the ability to form rotary driven cylindrical cutter devices of small diameter. 
     Another feature of the apparatus is that the threaded opening in the base receiving the retainer can be defined by a removable insert having internal threads designed to engage the fastener securing the retainer in place. The removable character of the insert ensures that the drum can quickly be refurbished in the field, if necessary, in the event of any damage to the fastener engaging threads. 
     These and other 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 drum having a plurality of cutting bit and retainer pairs received in overlapping recesses, one of the cutting bit and retainer pairs shown in exploded view. 
         FIG. 2  is an enlarged, perspective view of one of the cutting bits showing a retainer engagement feature on a lower portion of the cutter bit. 
         FIG. 3  is an enlarged, perspective view of one of the retainers showing a tooth engagement feature on a side thereof. 
         FIG. 4  is a sectional view of a drum with one of the cutting bit and retainer pairs received in overlapping recesses. 
         FIG. 5  is a perspective view of a drum with a slide hammer engaged into a retainer to extract the retainer and associated cutting bit from the drum. 
         FIG. 6  is a sectional view of a drum similar to  FIG. 4  showing a removable insert having internal threads designed to engage the fastener securing the retainer in place. 
     
    
    
     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 drum  10  without flighting having a plurality of cutting bit  12  and retainer  14  pairs received in overlapping recesses  16 ,  18  in the drum  10 . The recesses  16  and  18  are shown in  FIG. 1  to consist of overlapping right cylindrical depressions into the drum  10 . One of the cutting bit and retainer pairs is shown in exploded view to illustrate one embodiment of an apparatus  20 . The cutting bit and retainer pairs can be used on any portion of a cylindrical surface  22  of a milling or mining drum  10 , which is adapted to be rotated in a cutting direction R about a cylindrical axis X concentric to the drum surface  22 . 
     One embodiment of the cutting bit  12  is shown in  FIG. 2  to include a pedestal  24  that is shown to be generally cylindrical and includes a retainer engagement feature  26  on a lower portion thereof. The retainer engagement feature  26  is shown as a planar surface  28  that is inclined slightly upwardly so that a lower chord line  30  on the surface is shorter than a parallel upper chord line  32 . The cutting bit  12  is also shown in  FIG. 2  to include a upper portion  34  that is shown to be conically tapered, but the upper portion  34  can be a continuation of the shape of the pedestal  24 . A cutting element  36  can be secured to protrude above an upper end  38  of the conically tapered upper portion. The cutting bit  12  is further shown in  FIG. 2  to have an additional laterally extending surface  40  located immediately above the retainer engagement feature  26  that facilitates the removal of the cutting bit  12  from the drum  10  as described below. 
     One embodiment of the retainer  14  is shown in  FIG. 3  to include a planar upper surface  42  that is perpendicular to a right cylindrical side surface  44 . A tooth engagement feature  46  occupies a portion of the side of the retainer  14  and is shown to consist of a planar surface  48  inclined slightly downwardly at an angle matching, but in the opposite direction of, planar surface  28  on cutting bit  12 . The retainer  14  also includes a hole  50  passing through the retainer  14  perpendicular to the upper planar surface  42  and symmetrically positioned with respect to the right cylindrical side surface  44 . The hole  50  can include an internal engagement feature  52 , which can be a set of threads  54 , adapted to engage a tool suitable for removing the retainer  14  from the drum  10  as discussed in more detail below. The retainer  14  also can include a tapered lower surface  56 , which may be better see in  FIG. 4 . 
       FIG. 4  is a sectional view of a drum  10  with one of a cutting bit  12  received in recess  16  and retainer  14  received in recess  18 . The cylindrical pedestal portion  24  of the cutting bit  12  is shown to be dimensioned to match the size of the recess  16 , while the upper portion  34  extends above the surface  22  of the drum  10 . The cylindrical side surface  44  of the retainer  14  is dimensioned to match the size of the recess  18 , while the vertical dimension of the retainer is such that the planar upper surface  42  is recessed below the surface  22  of the drum  10 . The tooth engagement feature  46  of the retainer  14  engages in an abutting arrangement the retainer engagement feature  26  of the tooth or cutting bit  12 . A fastener  58 , which can be a screw, can secure the retainer  14  in the recess  18  so that the tooth engagement feature  46  engages the retainer engagement feature  26  to lock the cutting bit  12  in a desired position with respect to the drum surface  22 . The fastener  58  is preferably of a smaller diameter than hole  50  so that the fastener passes freely through the hole to engage an opening  60  in the bottom  15  of recess  14 . The fastener  58  can include a washer  62  to provide a broad bearing surface on the top of the planar upper surface  42  of the retainer  14 . 
       FIG. 5  is a perspective view of a drum  10  with a slide hammer  64  engaged into hole  50  of retainer  14  to extract the retainer  14  and associated cutting bit  12  from the drum  10 . The slide hammer  64  includes a shaft  66  having a lower end engaging hole  50  of the retainer  14  and an upper end  68  including an enlarged head  70 . A slide weight  72  is situated on the shaft  66  so as to be reciprocally movable along the shaft, and, in particular, to repeatedly impact the enlarged head  70 . The repeated impact will act to extract the retainer  14  from the recess  18 . As the retainer  14  moves outward, an edge of the planar upper surface  42  of the retainer  14  will come in contact with the laterally extending surface  40  located immediately above the retainer engagement feature  26 . Consequently, the outward movement of the retainer  14  forces the associated cutting bit  12  from the drum  10 . 
     An alternative to the use of an slide hammer  64  is the engagement of an elongated extraction screw, not shown, in the hole  50  of retainer  14 . The elongated extraction screw can have a lower end designed to abut the bottom  15  of recess  18 . An impact wrench, or other tool, can then advance the extraction screw, which advance has the effect of backing the retainer  14  out of recess  18 . As the retainer  14  moves outward, an edge of the planar upper surface  42  of the retainer  14  comes into contact with the laterally extending surface  40  located immediately above the retainer engagement feature  26 . Consequently, the outward movement of the retainer  14  forces the associated cutting bit  12  from the drum  10 . 
       FIG. 6  is a sectional view of a drum  10  similar to  FIG. 4  showing a removable insert  65  having internal threads  66  designed to engage the fastener  58  securing the retainer  14  in place in the recess  18 . The removable insert  65  can have an outer engagement surface  69  designed to cooperatively engage a corresponding interior engagement surface  71  in opening  60 . The cooperatively engaging surfaces  69  and  71  can be, for example, threads, preferably of a different pitch than the internal threads  66  engaging the fastener  58 , and possibly of a hand opposite that of the internal threads  66 . The removable character of the insert  65  ensures that the drum  10  can quickly be refurbished in the field, if necessary, in the event of any damage to the fastener engaging threads  66 . This avoids the necessity of having to possibly re-tap the threads of opening  60  shown in  FIG. 4  in the event of damage to the threads. As in  FIG. 4 , the pedestal portion  24  of the cutting bit  12  is shown to be dimensioned to match the size of the recess  16 , while the upper portion  34  extends above the surface  22  of the drum  10 . The side surface  44  of the retainer  14  is dimensioned to match the recess  18 , while the vertical dimension of the retainer is such that the planar upper surface  42  is recessed below the surface  22  of the drum  10 . The tooth engagement feature  46  of the retainer  14  engages in an abutting arrangement the retainer engagement feature  26  of the tooth or cutting bit  12 . The fastener  58  can secure the retainer  14  in the recess  18  so that the tooth engagement feature  46  engages the retainer engagement feature  26  to lock the cutting bit  12  in a desired position with respect to the drum surface  22 . The fastener  58  passes freely through the hole  50  in the retainer  14  to engage the internal threaded portion  66  of removable insert  65 . The fastener  58  can include a washer  62  to provide a broad bearing surface on the top of the planar upper surface  42  of the retainer  14 . 
     It will be noted from  FIGS. 1 ,  5  and  6  that the diameter of the retainer receiving recess  18  is greater than the diameter of the cutting bit receiving recess  16 . The relative sizes of the recesses are a matter of design choice, and the relative sizes can be reversed or maintained equal. It will also be noted from  FIGS. 1 ,  5  and  6  that the recesses are cylindrical in shape, but again this is a matter of design choice, and other shapes might be used for either or both of the recesses  16 ,  18 , so long as the pedestal  24  of the cutting bit  12  and the retainer  14  are suitably shaped to correspond to the shape and size of the recesses  16 ,  18 . It will also be noted from  FIGS. 1 ,  5  and  6  that the recesses  16 ,  18  are aligned along a circumference line extending around the cylindrical surface  22  of the drum  10 , with the retainer  14  in advance of the cutting bit  12 . The relative position of the retainer  14  and cutting bit  12  is a matter of design choice. The retainer could be positioned behind or beside the cutting bit so long as the retainer engagement surface  26  and the laterally extending surface  40  on the cutting bit  12  were suitably repositioned. It will be noted from  FIGS. 1 ,  2 , and  4  that the cutting bit  12  includes a cutting element  36  having an broad upper edge generally parallel to the surface  22  and having a negative rake angle with respect to the cutting direction of drum  10 . The configuration of the cutting element  36  is also a matter of design choice, and the cutting element can have any desired configuration that is thought to be particularly suitable for the intended use. 
     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

Summary:
A milling drum adapted to be rotated in a cutting direction about an axis defined by the cylindrical surface of the drum. A plurality of pairs of overlapping recesses in the cylindrical surface of the drum. A tooth or cutting bit with a base configuration matching a first of the pair of the overlapping recesses, and a lower portion of a side surface including a retainer engagement feature. A retainer has a base configuration matching a second of the pair of overlapping recesses, and a side surface including a tooth engagement feature. A fastener secures the retainer in the second of the overlapping recesses so that the tooth engagement feature of the retainer engages the retainer engagement feature of the tooth or cutting bit to hold the tooth or cutting bit in the first of the overlapping recesses.