as shown in fig1 . and 3 , the shear shredder of the present invention , generally designated 10 , includes a support frame 12 , which is mounted above grade on four support legs 14 . the support legs 14 are part of a base frame 16 which supports the frame 12 . the support frame 12 receives removable side walls 18 , 20 and removable end housings 22 , 24 . the side walls 18 , 20 preferably are bolted to the frame 12 , as are the end housings 22 , 24 . the support frame 12 , side walls 18 , 20 and end wall housings 22 , 24 form an enclosure , generally designated 26 , having an open top 28 which allows material to enter the interior grinding chamber 30 of the shear shredder . a hopper 32 having downwardly - converging side walls 34 , 36 , 38 , 40 is mounted on the shredder housing 26 and communicates with the open top 28 . the grinding chamber 30 is defined by the side walls 18 , 20 and grinding chamber end walls 42 , 44 . the frame end walls 46 , 48 are removably attachable to the ends of the support frame 12 by bolts or machine screws ( not shown ), and support drive motors 50 , 52 , 54 , 56 , respectively . the end walls 46 , 48 are attached to u - shaped brackets 57 which are machined for precision and welded to the frame 12 in precise alignment with respect to each other . in the preferred embodiment , the walls 46 , 48 are dowelled for location . the side walls 18 , 20 are also removably attachable to the support frame 12 by bolts or machine screws , ( not shown ). each of the side walls 18 , 20 supports a plurality of spaced comb elements 59 . comb elements 59 are separate by spacers 60 and are retained on side walls 18 , 20 by rails 61 , bolted to the walls , which capture tabs protruding from the base of the elements . a pair of shear cartridges 62 , 64 are mounted within the support frame 12 . as shown in fig2 and 4 , each shear cartridge includes a hexagonal shaft 66 on which is mounted a plurality of cutter elements 68 , each of the cutter elements being separated from its neighbor by a spacer ring 70 . the cutter elements 68 and spacer rings 70 each include hexagonal central openings to prevent rotation relative to the shaft 66 . outside of the array of cutter element 68 and spacers 70 are small 72 and large 74 stack tighteners . the small and large stack tighteners 72 , 74 each have a central , hexagonal opening to receive the shaft 66 , and large stack tighteners 74 include a peripheral flange 76 . the array of cutter elements 68 , spacer 70 and stack tighteners 72 , 74 are held on the shaft 66 by end caps 78 , 80 . end caps 78 , 80 are retained on the ends of the shaft 66 by screws 82 , 84 , respectively . jam nut and wedge bolt combinations 86 extend between the end cap 80 and stack tightener 72 , 74 . the jam nut and wedge bolt combinations are adjusted to urge the stack tighteners 72 , 74 inwardly toward the shaft 66 to tighten the cutter elements 68 and spacers against each other . as shown in fig1 and 2 , the shear cartridges 62 , 64 are positioned within the support frame 12 so that the stack tighteners 72 , 74 are adjacent to the grinding chamber end walls 42 , 44 . the flange on stack tightener 74 is adjacent to a spacer 70 and serves as a shield to prevent contaminants from passing through the wall 42 . the walls 42 , 44 each include inserts 88 , 90 , 92 , 94 which complete the continuity of the end walls 42 , 44 to define the grinding chamber 30 . each of the hydraulic drive motors 50 - 56 includes a flat attachment plate 96 mounted on its output shaft . the flat plates 96 bolt to the faces 98 of the end caps 78 , 80 of the shear cartridges 62 , 64 . as shown in fig5 for end wall 46 , the end walls 46 , 48 include openings 100 , 102 which receive the housings 104 of the motors 54 , 56 . the housing flanges 106 of the motors 54 , 56 are ground to permit close spacing of the motors and are attached to the walls by bolts or machine screws ( not shown ). as shown in fig1 , the hopper 32 includes a feed ram , generally designated 108 , which is mounted on hopper side wall 34 . side wall 34 includes longitudinal reinforcing bars 110 , 112 and lateral struts 114 , 116 , which extends between the reinforcing bars , and frame and opening 118 formed in the side wall 34 . a primary double - acting cylinder 120 is mounted so that a first cylinder rod 122 is attached to lateral strut 116 and second and third rods 124 are attached to a slider plate 126 ( see also fig7 and 10 ). the cylinder 120 is covered by access plate 127 . such a cylinder 120 is shown in greater detail in co - pending u . s . patent application ser . no . 07 / 993 , 123 , filed dec . 21 , 1992 , the disclosure of which is incorporated herein by reference . the slider plate 126 is shaped to cover the opening 11 - 8 completely when cylinder rod 122 is extended and retracted . secondary cylinders 128 ( see fig1 ) are pivotally mounted on slider plate 126 and include rods 130 which are pivotally attached to a ram assembly , generally designated 132 . ram assembly includes a ram face 134 which is pivotally attached to a support frame 136 having legs 138 which telescope into sections 140 of the slider plate 126 . a ram shield 142 is pivotally connected to the ram face 134 at a lower end and is pivotally connected to the slider plate 126 at an upper end . the slider plate and ram assembly 132 are covered by a plate 144 . the plate 144 and shield 142 act together to prevent waste material from falling behind the ram face 134 . as shown in fig8 when the secondary cylinder 128 is retracted , the ram assembly is drawn upwardly relative to the slider plate 126 . this causes the ram face 134 to pivot toward the side wall 34 of the hopper 32 . at the same time , the shield 142 pivots relative to the slider plate 126 as well , and forms a substantially planar surface with plate 144 . in this collapsed configuration , the feed ram 108 presents a low profile and a minimal obstruction within the hopper 32 . as shown in fig7 when it is desired to activate the feed ram 108 , the secondary cylinders 128 are actuated to extend their rods 130 , thereby displacing the ram assembly downwardly relative to the slider plate 126 . this relative movement causes the ram face 134 to pivot outwardly to an operative position . the ram face may then be reciprocated relative to the hopper 32 and side wall 34 by primary cylinder 120 to urge material downwardly through the open top 28 and into the grinding chamber 30 ( see fig1 ) of the shear shredder 10 . the system for powering the various components of the shear shredder 10 is shown schematically in fig6 . a pair of drive motors 146 , 148 each power a pair of pumps 150 , 152 , 154 , 156 , respectively . in addition , electric drive motor 148 powers pump 158 which supplies hydraulic pressure through valves 160 , 162 to the cylinders 120 , 128 in the feed ram 108 ( see also fig1 ). pumps 1 - 50 , 152 are connected to and supply pressurized hydraulic fluid to hydraulic cartridge drive motors 50 , 52 , respectively . similarly , hydraulic pumps 154 , 156 are connected to and supply pressurized hydraulic fluid to hydraulic cartridge drive motors 54 , 56 respectively . consequently , each of the shear cartridges 62 , 64 receives power from both electric drive motors 146 , 148 . specifically , shear cartridge 62 is rotated by drive motors 54 , 50 and shear cartridge 64 receives rotational power from drive motors 56 , 52 . as a result of this arrangement , should either of the shear cartridges 62 , 64 become jammed , the power from both of the motors 146 , 148 is directed to the hydraulic drive motors powering that shear cartridge . thus , smaller electric drive motors 146 , 148 may be used since their power is combined in operational conditions which require greater power . as a result of the structure of the shear shredder , the insertion and replacement of the shredder cartridges 62 , 64 is facilitated . for example , should it be necessary to replace shear cartridge 62 in the field , the following sequence of steps is performed . first , side wall 18 is removed from the support frame 12 , which disengages the associated comb elements 59 from the cutter elements 68 of cartridge 62 . inserts 88 , 92 are unbolted from engagement with end walls 42 , 44 . if necessary , the stack tighteners 72 , 74 are loosened by appropriate adjustment of the screws 86 , which allows the cutter elements 68 to separate from the spacer elements 70 slightly . this step may be performed prior to the removal of side wall 18 in order to facilitate disengagement with the comb elements 60 . the cartridge 62 is then supported by a jack ( not shown ) to cradle it and the end caps 78 , 80 are unbolted from their connection to the face plates 96 of the hydraulic drive motors 50 , 54 . the cartridge 62 can then be removed from the support frame 12 by a fork lift or the like . the end walls 46 , 48 are also easily removable . in order to assure proper alignment , in the preferred embodiment , the end walls 46 , 48 are located in position with high precision by dowel pins ( not shown ). in order to remove the end walls 46 , 48 , they are unbolted , the dowel pins removed and the end walls , along with the drive motors 50 - 56 can be lifted upwardly by a crane . of course , the upward removal of the end walls 46 , 48 requires removal of the end wall housings 22 , 24 from the support frame 12 . it is apparent , therefore , that the cartridges 62 , 64 are modular in design and can be reversed end - for - end and inserted in the support frame 12 , if required . further , the shear cartridges 62 , 64 can be of identical construction and selected from among an inventory of identical shear cartridges . similarly , the end walls 46 and 48 and motors 50 - 56 are modular in construction and can be selected from among an inventory of substantially identical components . for proper alignment of the end walls 46 , 48 which is desired to effect a proper alignment of the shear cartridges 62 , 64 , the portions of the support frame 12 which receive the end walls 46 , 48 only need to be machined to a high precision , and not other components of the frame . also in the preferred embodiment , the hydraulic drive motors 50 , 52 , 54 , 56 are controlled by the use of swash plates , rather than valves , which promotes efficiency of operation . although described above as a shear shredding apparatus , it will be apparent to those of ordinary skill in the art that the novel aspects of the present invention apply to other material processing apparatuses having a pair of co - acting , substantially parallel , counter - rotating rotor assemblies , such as briquetting apparatuses , grinding apparatuses and the like . in particular , it will be a conventional exercise for those of ordinary skill in the art to replace the shear cartridges 62 , 64 with counter - rotating , co - acting briquette rolls , grinding rolls and the like . fig1 - 13 illustrate an alternate embodiment of the present invention 164 , which provides a first roller assembly that is laterally adjustable with respect to a second fixed roller assembly . the roller assemblies illustrated in this alternate embodiment are briquetting rolls , however , as described above is within the scope of the invention to use shear shredding cartridges , grinding rolls , and any other similar material processing roll as will be known to those of ordinary skill in the art . as shown in fig1 - 13 , the material processing apparatus 164 includes a support frame 166 which receives removable side walls 168 , 170 and removable end bearing housings 172 , 174 . the side walls 168 , 170 preferably are bolted to the frame 166 , as are the end bearing housings 172 , 174 . the support frame 166 , side walls 168 , 170 and end bearing houses 172 , 174 form an enclosure , generally designated 176 , having an open top 178 which allows material to enter the material processing chamber 180 of the area processing apparatus 164 . material processing chamber 180 is defined by side walls 168 , 170 and processing chamber end walls 182 , 184 . the end bearing housing 174 supports a pair of drive motors assemblies 186 , 188 , where each drive motor assembly 186 , 188 respectively includes bearing and shaft assembly 190 , 191 a reversible hydraulic drive motor 192 , 193 and a motor housing 194 , 195 . the other end bearing housing 172 supports a pair of bearing assemblies 196 , 198 . it will be apparent to one of ordinary skill in the art that the bearing assemblies 196 , 198 may be replaced by a second pair of drive motor assemblies as described above . the bearing assemblies 190 , 191 , 196 , 198 include unique stave bearings 199 , which are described in detail in u . s . pat . no . 6 , 000 , 852 . a pair of substantially cylindrical , material processing roller assemblies 200 , 202 are mounted within the support frame 166 . end caps 208 , 209 are retained on the ends of each roller assembly 200 , 202 . the hexagonal shaft 210 of each bearing / shaft assembly 190 , 191 , 196 , 198 extends through a cylindrical hole 211 in the respective end bearing housing 172 , 174 , and is coupled to a corresponding attachment plate 212 . the attachment plates 212 are , in turn , bolted to the faces of the end caps 208 , 209 of the material processing roller assemblies 200 , 202 . the walls 182 , 184 each include inserts 214 , 216 , ( 218 not shown ), 220 to complete the continuity of the end walls 182 , 184 and to define the material processing chamber 180 . as is discussed in greater detail below , each end bearing housing 172 , 174 includes a fixed bearing support member 222 and an adjustable bearing support member 224 , which is laterally adjustable with respect to the fixed bearing support member 222 . finally , the apparatus 164 includes removable top and bottom panels 226 , 228 , respectively for isolating the material processing chamber 180 from the remainder of the material processing apparatus 164 . as shown in fig1 and 15 , each end bearing housing 172 , 174 includes a fixed bearing support 222 and an adjustable bearing support 224 . fixed bearing support 222 is integral with or fixedly attached to a frame 230 . the frame 230 includes a lateral surface 232 extending laterally from the fixed support member 222 slidably receiving the adjustable support member 224 , and the frame further includes a fixed member 234 distal from the bearing support 222 and perpendicular to the lateral surface 232 . the frame further includes a top opening 236 for receiving the adjustable bearing support . when the adjustable bearing support 224 is seated on the lateral surface 232 , a shim 238 is positioned on a lateral side 240 of the adjustable bearing support , between the adjustable bearing support 224 and the fixed bearing support 222 . on the opposite lateral side 242 of the adjustable bearing support a hardened plate 244 and a torque plate 246 are positioned between the adjustable bearing support 242 and the fixed member 234 of the frame 230 . the torque plate 246 includes a plurality of threaded bores 248 extending laterally therethrough for receiving a corresponding plurality of threaded bolts 250 . the bolts 250 are received through a lateral opening 252 extending through the side of the frame 230 . as shown in fig1 , as the bolts 250 are threaded through the torque plate 246 and abut against the hardened plate 244 the continuous turning of the bolts causes the torque plate 246 to abut against the fixed member 234 of the frame 230 . accordingly , further tightening of the bolts 250 causes the hardened plate 244 and torque plate 246 to be forcefully separated from one another , and in turn causes the hardened plate 244 to apply lateral pressure against the adjustable bearing support 224 in the direction of the shim 238 and fixed bearing support 222 . and upon sufficient tightening of the bolts 250 , the adjustable bearing support 224 will be fixed with respect to the fixed bearing support 222 , having the shim 238 being fixed therebetween . accordingly , by adjusting the thickness of the shim 238 , the operator will be able to adjust the lateral separation between the fixed bearing support 222 and the adjustable bearing support 224 . for example , when the present apparatus 164 is used as a briquetting machine , the new briquetting rolls 200 , 202 , are installed into the apparatus 164 a new shim having a predefined thickness will be likewise mounted between the fixed bearing support 222 and the adjustable bearing support 224 . thereafter , as the briquetting rolls wear down , the operator will be able to move the briquetting rolls closer together by loosening the bolts 250 , removing the shim 238 from between the fixed bearing support 222 and the adjustable bearing support 224 , machining the shim 238 to the desired thickness , re - inserting the shim 238 between the fixed bearing support 222 and the adjustable bearing support 224 , and then re - tightening the bolts 250 . while the form of apparatus herein described constitutes a preferred embodiment of the invention , it is to be understood that other forms of apparatus may be employed without departing from the scope of the invention .