Abstract:
A method of assembling an idler roll having an outer shell and end bearing assemblies. The bearing assemblies each have an outer race and an inner race. The inner race is press fitted onto a roller shaft to an initial position which is spaced inwardly from a final desired position. The outer shell of the roll is restrained and the shaft is reciprocated along its longitudinal axis to determine the degree of axial movement. The inner race of the bearing assembly is moved from its initial position to its final position as determined by the degree of axial movement.

Description:
This application claims priority based on U.S. Provisional Application Ser. No. 60/148,197, filed Aug. 10, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to idler rollers for conveyors and, more particularly, to bearing assemblies for such idler rollers. 
     A belt conveyor is conventionally supported between its ends by a plurality of carriers. Each carrier typically includes a frame extending transversely to the conveyor belt and journals generally three idler rolls in an end-to-end relationship. Generally, the intermediate idler roll is disposed in a horizontal position while the outer two idler rolls are disposed at an upwardly inclined angled relationship to a horizontal plane to give the conveyor belt a trough-like shape for the purpose of keeping a load centered on the conveyor belt. 
     The idler rolls typically have bearing assemblies, which are interposed between a rotating roller shell and a stationary shaft. While the bearing assemblies are commonly ball bearings, it is desirable for the bearing assemblies to be tapered roller bearings because they can provide twice the minimum life of ordinary ball bearings. The tapered roller bearings, however, require precise axial clearance settings. The tapered roller bearings have been secured with threaded assemblies and/or snap rings with compensating washers to account for manufacturing variations. Thus the idler rolls with tapered roller bearings are relatively complex to produce and are relatively expensive. 
     It is generally known to press various bearings onto various shafts. This is a rather simple and low-cost approach. The long shaft lengths of idler rolls, however, have made press fitting tapered roller bearings directly onto the metal shaft impractical because of the precise axial clearance seating required versus shaft flexibility and compressibility. 
     Accordingly, there is a need in the art for an idler bearing having tapered roller bearings that have precise and consistent end-play settings, is relatively easy to produce, and is affordably priced. There is also a need in the art for a method of producing such idler bearings and a device for automatically producing a high volume of such idler rolls. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     These and further features of the present invention will be apparent with reference to the following description and drawings, wherein: 
     FIG. 1 is a sectional view of an idler roll assembly for a troughing belt conveyor loaded with bulk material according to the present invention; 
     FIG. 2 is an enlarged front elevational view, partly in cross section, showing a single idler roll of the idler roll assembly of FIG. 1; 
     FIG. 3 is a side view of the idler roll of FIG. 2; 
     FIG. 4 is an enlarged front elevational view, in cross section, showing one end of the idler roll of FIG. 2; 
     FIG. 5 is an enlarged perspective view of one end of the idler roll of FIG. 2 with portions cut away and the shell removed for clarity; 
     FIG. 6 is an enlarged front elevational view, partly in cross-section, showing a shell of the idler roll of FIG. 2; 
     FIG. 7 is an enlarged front elevational view, in cross-section, showing a head assembly of the idler roll of FIG. 2; 
     FIG. 8 is an enlarged front elevational view showing a shaft of the idler roll of FIG. 2; 
     FIG. 9 is a cross-sectional view showing a multi-station machine for assembling the idler roll of FIG. 2, the plane of the section being indicated by the line  9 — 9  in FIG. 9 a;    
     FIG. 9 a  is a top plan view of the multi-station machine; 
     FIGS. 10 and 11 are side elevational views similar to FIG. 9 but showing the machine in progressively indexed positions during assembly of the idler roll; 
     FIG. 12 is a cross-sectional view, the plane of the section being indicated by the line  12 — 12  in FIG. 9; 
     FIG. 13 is an end view of the machine; 
     FIG. 14 is a cross-sectional view, the plane of the section being indicated by the line  14 — 14  in FIG. 9 a;    
     FIG. 14 a  is an enlarged fragmentary view of a portion of the assembly shown in FIG. 14; 
     FIG. 14 b  is a cross-sectional view, the plane of the section being indicated by the line  14   b — 14   b  in FIG. 14 a;    
     FIG. 15 is an elevational view of a single lift unit; 
     FIG. 15 a  is a plan view of the unit illustrated in FIG.  15 ; 
     FIG. 16 is an elevational view of a double lift unit; 
     FIG. 16 a  is a plan view of the unit illustrated in FIG. 16; 
     FIG. 17 is an end view of a double lift unit, the plane of the view being illustrated by the line  17 — 17  in FIG. 16; 
     FIG. 18 is an enlarged cross-sectional view of a bearing being press fit on a roll shaft; 
     FIG. 18 a  is a view similar to FIG. 18 but showing a later stage of the press fit operation; 
     FIG. 19 is a cross-sectional view, the plane of the section being indicated by the line  19 — 19  in FIG. 9 a;    
     FIG. 20 is a plan view of the assembly shown in FIG. 19; 
     FIG. 21 is an enlarged plan view of the bearing press tool; and 
     FIG. 22 is an end view, the plane of the view being indicated by the line  22 — 22  in FIG.  19 . 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an idler roll assembly  10  of a troughing belt conveyor loaded with bulk material  12 . The idler roll assembly  10  includes three idler rolls  14  for supporting a conveyor belt  16  and a rigid carrier frame  18  for supporting the idler rolls  14 . The carrier frame  18  has a plurality of vertically disposed frame members  20  supporting ends of the idler rolls  14 . While the invention is illustrated as being applied to three roll troughing idlers, it should be appreciated that the invention is also applicable to flat return rolls and idler rolls in general. 
     Each of the idler rolls  14  are preferably constructed in an identical manner, therefore, only will be described in detail hereinafter. As best shown in FIGS. 2-5, each idler roll  14  includes a roll cylinder or shell  22 , a pair of end or head assemblies  24 , a shaft  26 , and a pair of exterior shields  28 . 
     As best shown in FIG. 6, the roll shell  22  preferably has a wall  30  forming a hollow cylinder with open ends. The wall  30  is provided with a counterbore  32  at each end to form opposed annular shaped and outward facing abutments  34 . The counterbore  32  is sized to form a seat for and press fit with the head assembly  24  as described in more detail hereinafter. The roll shell  22  typically has an outer diameter of about 4 inches to about 6 inches, a length of about 5 inches to about 81 inches, a wall thickness of about 0.148 inches to about 0.250 inches (about 9 to about ¼ tube gauge). 
     As best shown in FIG. 7, each head assembly  24  includes a roll end or head  36 , a bearing assembly  38 , a back or inside seal  40 , an outside seal  42 , and a lip seal  44 . The roll head  36  has a cap portion  46  and an integral hub portion  48  inwardly extending from the cap portion  46  to form a recess for receiving the bearing assembly  38 . The cap portion  46  is sized and shaped to be press fit into the counterbore  32  of the. roll shell  22 . The cap portion  46  has an outer diameter sized for an interference fit with the roll shell  22 , such as an interference of preferably about 0.002 to about 0.010 inches and more preferably about 0.005 to about 0.008 inches. For example, a roll shell  22  having an outer diameter of 5 inches can have a counterbore diameter of 4.817/4.820 inches to mate with a roll head  36  having an outer diameter of 4.822/4.827. The hub portion  48  is generally cylindrical-shaped and is sized to form a seat for and press fit with the bearing assembly  38  as described in more detail hereinafter. The inner or free end of the hub portion  48  is provided with a lip or flange  50 . The flange  50  extends radially inward to form an outwardly facing abutment  52  at the rear of the recess formed by the hub portion  48 . 
     The bearing assembly  38  is preferably a single row, straight bore tapered roller bearing including an outer race or cup  54 , an inner race or cone  56 , a plurality of tapered rollers  58  between the cup  54  and the cone  56 , and a cage  60  for the rollers  58 . The bearing assembly may contain ball bearings. The cup  54  has an outer diameter sized to be press fit into the recess of the roll head hub portion  48 . Preferably, the cup  54  has an outer diameter sized for an interference fit with the roll head hub portion  48  such as an interference of about 0.005 to about 0.008 inches. The cone  56  has an inner diameter sized to form a press fit with the shaft  26  as described in more detail hereinafter. The bearing assembly can be a standard type TS bearing with class 4 tolerances but preferably has a front face radius or chamber  62  which allows the cone  56  to be pressed over the shaft  26  with an interference, preferably of up to about 0.003 inches, without shaving a burr off of the shaft  26 . For example, a ¾ inch bearing assembly  38  can have a front face radius  62  of about 0.03 inches to about 0.05 inches or a front face chamber can have an angle of about 15° and a depth up to about 0.05 inches. 
     The back seal  40  is adapted to provide protection for the bearing&#39;s grease reservoir at the rear or inner side of the bearing assembly  38 . The back seal  40  is sized and shaped to generally close the annular shaped gap between the hub portion  48  of the roll head  36  and the shaft  26 . The back seal  40  preferably has a generally tubular-shaped main wall  64 , a radially outwardly extending flange  66  extending from a forward end of the main wall  64 , and a radially inward extending lip  68 . The flange  66  is sized to be held between the flange  50  of the roll head hub portion  48  and the rear end of the bearing assembly cup  54 . Preferably, the back seal flange  66  is compressed between the flange  50  of the roll head hub portion  48  and the rear end of the bearing assembly cup so that it is rigidly held thereto for rotation therewith. The lip  68  is sized and shaped to engage the stationary shaft  26 . The back seal  40  can be formed from any suitable resilient material such as, for example, an elastomer. 
     The outside seal  42  is adapted to cooperate with the exterior shield  28  to form a labyrinth passage  70  which retards lateral movement of contaminants and to utilize the natural centrifugal forces of the rotating idler roll  14  to redirect potential contaminants away from the labyrinth passage  70 , that is to act as a flinger. The outside seal  42  preferably has a generally tubular shaped main wall  72 , a radially inwardly extending flange  74  extending from the main wall  72 , and a plurality of forwardly extending fingers  76  extending from the forward side of the flange  74 . The main wall  72  is sized to engage the inner diameter of the hub portion  48  of the roll head  36  when inserted therein. Preferably, the main wall  72  has an outer diameter sized for at least a tight press fit with the inner diameter of the roll head hub portion  48  so that it is rigidly held thereto for rotation therewith. The main wall  72  preferably has a length sized to extend from the forward end of the bearing cup  54  to a plane forward of the roll head  36  so that the forward end of the main wall  72  is cantilevered from the roll head hub portion  48 . The free forward end of the main wall  72  is sized and shaped to redirect potential contaminants radially outward away from the main wall  72  and the labyrinth passage  70  by utilizing centrifugal forces. In this regard, the outer surface of the main wall  72  curves radially outward in a forward direction at the forward end of the main wall  72 . The cylindrically shaped fingers  76  are concentric and spaced apart and are sized and shaped to cooperate with the exterior shield  28  to form the labyrinth passage  70 . The outside seal  42  can be formed from any suitable material such as, for example, a molded thermoplastic material. 
     The lip seal  44  is located between the flange  74  of the outside seal  42  and the forward end of the bearing assembly  38  and is adapted to provide further protection against intrusion by contaminants. The lip seal  44  is sized and shaped to generally close the annular shaped gap formed between the main wall  72  of the outer seal  42  and the shaft  26  rearward of the labyrinth passage  70 . The lip seal  44  preferably has a tubular shaped main wall  78  and a radially inward extending lip  80  extending from the forward end of the main wall  78 . The main wall  78  is sized to engage the inner diameter of the outer seal main wall  72  when inserted therein. An anchoring ring or insert  82  is provided at the inner diameter of the main wall  78  which is sized to compress the main wall  78  of the lip seal  44  against the main wall  72  of the outside seal  42  so that it is rigidly held thereto for rotation therewith. The lip  80  is sized and shaped to engage the exterior shield  28 . The lip seal  44  can be formed from any suitable resilient material such as, for example, an elastomer. 
     As best shown in FIGS. 2 and 8, the shaft  26  is a solid bar preferably having a length greater than the roll shell  22  and a constant outer diameter sized for a press fit with the bearing assembly cone  56 . The shaft  26  may be a hollow and/or an end point shaft without departing from the invention. The illustrated shaft  26  is provided with a pair of opposed flats  84  on each end for cooperating with the frame members  20  of the carrier frame  18 . Typically, the shaft  26  has a length of about 8⅜ inches to about 58⅜ inches for a roll shell  22  having lengths of 7 inches to 57 inches. The shaft  26  preferably has an outer diameter sized for an interference fit with the bearing cup  54  such as an interference of up to about 0.003 inches and more preferably an interference of up to about 0.0005 inches to about 0.0030 inches. For example, a bearing cone  56  having an inner diameter of 0.750+0.0005/−0.0000 inches can mate with a shaft  26  having an outer diameter of 0.7510/0.7530 inches. The shaft can be formed from any suitable material such as, for example, C1018 or C1040 steel or the like. 
     As best shown in FIGS. 2-5, the exterior shield  28  is adapted to cooperate with the outside seal  42  to form the labyrinth passage  70  which retards lateral movement of contaminants and is adapted to close the outer end of the idler roll  14 . The exterior shield  28  is sized and shaped to generally close the annular shaped gap between the roll head  36  and the shaft  26  at the end of the idler roll  14 . The exterior shield  28  preferably has a generally tubular shaped main wall  86 , a radially outwardly extending flange  88  extending from the forward end of the main wall  86 , a plurality of rearwardly extending fingers  90  extending from the rearward side of the flange  88 , and an inwardly extending lip  92  extending from the free outer end of the flange. The main wall  86  is sized to engage the outer diameter of the shaft  26  when inserted thereon. Preferably, the main wall  86  has an inner diameter sized for at least a tight press fit with the shaft  26  so that it is rigidly held thereto and stationary therewith. The main wall  86  preferably has a length sized to extend from the forward end of the bearing cone  56  to a plane forward of the outside seal fingers  76 . The cylindrically-shaped fingers  90  are concentric and spaced apart and are sized and shaped to cooperate with the fingers  76  of the outside seal  42  to form the labyrinth passage  70 . The lip  92  is sized and shaped to engage the forward or outer surface of the rotating cap portion  46  of the roll head  36 . The exterior shield  28  can be formed from any suitable material such as, for example, at least in part a molded thermoplastic material. 
     FIGS. 9-22 illustrate a multi-station assembly machine  100  for automatically producing a high volume of the idler rolls  14 . The machine  100  includes ten stations, but a greater or lesser number of stations can be utilized within the scope of the invention. 
     The machine  100  includes a base frame  102  having a stationary frame  104  and a moveable frame  106  mounted thereon. The moveable frame  106  is mounted on tracks  108  for movement between solid and phantom outline positions illustrated in FIG.  14 . Movement of the frame  106  is effected by a motor  110  mounted on the base frame  102  which drives a threaded shaft  112 . The shaft  102  is threaded through a guide block  111  fixed to the frame  106  to move the frame  106  along the tracks  108  and relative to upper and lower guide shafts  114  and  116 , respectively. 
     As may best be seen in FIGS. 9-11, an indexing shuttle  118  is provided. The indexing shuttle  118  comprises a main shuttle  120  and a feed shuttle  122 . The main shuttle  120  includes a plate frame  124  mounted on the stationary frame  104  and a plate frame  126  mounted on the moveable frame  106 . A carriage frame  128  is mounted for reciprocal movement on the plate frame  124 , and a carriage frame  130  is mounted for reciprocal movement on the plate frame  126 . To this end, the carriage frames  128  and  130  are provided with laterally extending rollers  132  and  134 , respectively, which roll in tracks  136  on the plate frames  124  and  126 . The carriage frames  128  and  130  are provided with a series of aligned roll cradles  138  which are adapted to receive and support an idler roll  14   a  being assembled. 
     An indexing mechanism is provided to index the carriage frames  128  and  130 , in unison, from the position illustrated in FIG. 9, to the position illustrated in FIG. 10, to the position illustrated in FIG. 11, and back to the position illustrated in FIG.  9 . The indexing mechanism includes a pair of pistons  140  each having a rod  142 . One of the pistons  140  is fixed to the plate frame  126  (FIG. 9) and the other piston  140  is fixed to the plate frame  124 . The rods  42  are connected to the carriage frames  128  and  130  by drive plates  144  and  146 , respectively. 
     In order to shift the main shuttle  120  from the fully extended position shown in FIG. 9 to the partially retracted position shown in FIG. 10, a piston stop member  148  having a limit switch  150  is raised by a piston  152  to position the switch  150  in the path of the plate  146 . When the plate  146  strikes the switch  150 , the piston  140  is deactivated to remain in the position shown in FIG.  10 . In this position, it will be noted that the main shuttle  120  has travelled a distance corresponding to the center-to-center spacing of the cradles  138 . In a typical installation, this spacing is 12 inches and the maximum extension or retraction of the rod  142  is 24 inches. 
     In order to shift the main shuttle  120  from the partially retracted position shown in FIG. 10 to the fully retracted position shown in FIG. 11, the piston  152  of the piston stop member  148  is retracted to release the limit switch  150  from contact with the plate  146  and the rod  142  is permitted to fully retract in its piston  140 . 
     The feed shuttle  122  includes a carriage frame  154  mounted for reciprocal movement on the plate frame  124  and a carriage frame  156  mounted for reciprocal movement on the plate frame  126 . The carriage frames  154  and  156  are provided with laterally extending rollers  158  and  160 , respectively, which roll in the tracks  136  on the plate frames  124  and  126 . The carriage frames  154  and  156  are provided with aligned roll cradles  160  which are adapted to receive and support roll shells  14   b  being loaded into the assembly machine. 
     The feed shuttle  122  is adapted to reciprocate between the position shown in FIG. 9 to the position shown in FIGS. 10 and 11. The movement between these positions corresponds to the center-to-center spacing between the roll cradles  138 . The feed shuttle  122  is retracted to the position shown in FIG. 9 by a piston (not shown) and is advanced to the position shown in FIGS. 10 and 11 by a spring and pulley mechanism  162  and a locating stop  164 . 
     The assembly machine has a load station  166 , a press cap station  168 , an idle station  170 , a first weld station  172 , a second weld station  174 , a first cool station  176 , a second cool station  178 , a check station  180 , a first unload station  182 , and a second unload station  184 . Loading working, idling, cooling, and unloading operations are conducted at an elevated level, while the roll workpiece transport operations are performed by the described indexing mechanism. Lift units are provided at each station to raise the roll assembly out of its roll cradle  160  to a working position and to lower the roll back to its cradle and retract from the roll to permit the indexing mechanism to shift the roll to a downstream work station. Single lift units are provided at the load station  166  the cooling stations  176  and  178 , and the check station  180  while double lift units  188  are provided at the press cap and idle stations  168  and  170 , and at the weld stations  172  and  174 . Each single lift unit  186  and each double lift unit  188  comprise identical end lift units  190  and  192 , and  194  and  196 , respectively. The end lift units  190  and  192  are mounted on the stationary frame  104  while the end lift units  194  and  196  are mounted on the moveable frame  106 . 
     Referring to FIGS. 15 and 15 a , the end lift  190  of a single lift unit  186  is illustrated. The end lift  190  comprises a base  198  fixed to the stationary frame  104 . A pair of pistons  200  mounted on the base  198  are adapted to raise and lower a roll cradle  202  between a lowered position, shown in solid outline, and a raised position, shown in phantom outline. The cradle  202  is fixed to a mounting plate  204  which is removeably fixed to a platform  206  by screw knobs  208 . Loosening of the knobs  208  permits the mounting plate  204  to be shifted so that the knobs  208  may clear apertures  210  in the plate  204 . The cradle may then be replaced by a differently sized cradle to accommodate a differently sized idler roll  14 . 
     Referring to FIGS. 16,  16   a  and  17 , the end lift  192  comprises a base  210  fixed to the stationary frame  104 . A pair of pistons  212  mounted on the base are adapted to raise and lower a pair of roll cradles  214  and  216  between a lowered position, shown in solid outline, and a raised position, shown in phantom outline. The cradles  214  and  216  are fixed to a mounting plate  218  which is removeably fixed to a platform  220  by screw knobs  222 . Loosening of the knobs  222  permits the mounting plate  218  to be shifted so that the knobs  222  may clear apertures  224  in the plate  218 . 
     As described thus far, the double lift unit  188  at the weld stations  172  and  174  is identical to the lift unit  188  at the press cap station and idle station  168  and  170 . At the press cap station  168 , there is further provided a shaft lift and support mechanism  226 . The mechanism  226  includes a shaft cradle  228  mounted on a platten  230 . The platten  230  is mounted on guide rods  232  and on a rod  234  associated with a power piston  236 . The power piston  236  is adapted to raise the shaft cradle from the position illustrated in solid outline in FIGS. 16 and 17 to the position illustrated in phantom outline. 
     In order to describe the tooling and the assembly steps performed at the various workstations, the transport of a workpiece through the machine  100  from the loading station  166  to the unloading stations  182  and  184  will now be described. At the loading station  166 , and with all of the single and double lift units  186  and  188  in their raised positions, a roll shell  22  is positioned in the roll cradles  202 . Prior to such positioning, the moveable frame  106  is moved along the tracks  108  so that the roll cradles  138  are spaced apart a distance sufficient to accommodate the length of the shell  22  (generally, between about 5 and 81 inches). A shaft  26  is placed in the shell  22 . The single lift unit  186  is lowered to place the shell  22  and the shaft  26  workpieces in the aligned roll cradles on the carriage frames  154  and  156  (see FIGS.  9  and  14 ). The main shuttle  120  and the feed shuttle are indexed from the position illustrated in FIG. 9 to the position illustrated in FIG. 10 in the previously described manner. The single and double lift units are activated to raise the shell  22  and the shaft  26  to the press cap station  168  as is shown in FIG. 14,  14   a  and  14   b . It should be noted that while the roll cradles  202  lift the shell  22  from the aligned roll cradles  160 , the shaft cradles  228  engage the ends of the shaft  26  to raise the shaft  26  to a centered position with respect to the shell  22 . 
     At the press cap station  168 , preassembled head assemblies  24  are delivered by a conveyor  240  and are pressed into the ends of the roll shell  22  and onto the ends of the shaft  26 . There are provided axially aligned press cap assemblies  242  at the station  168 . For purposes of simplicity, only the assembly  242  mounted on the moveable frame  106  is illustrated in FIG. 14 a . The assembly  242  includes a cylinder  244  and ram  246  which are mounted on a platform  248  and which are adapted to advance a power head  250  toward and away from the roll shell  22 . 
     The power head  250  has a spring loaded projecting shaft  252  which is adapted to be slideably received in the inner race  56  of the bearing. A robotic arm  254  having a gripping hand  256  is mounted on a piston  258  which in turn is mounted on a piston  260  for vertical and horizontal movement of the arm and hand  254  and  256 . The hand  256  grasps a preassembled head assembly  24  from the conveyor  240 , lowers the assembly and then translates horizontally to place the inner race  56  of the bearing over the projecting shaft  252 . With the assembly  24  in place on the shaft  252 , the power head  250  is advanced until the shaft  252  and the back seal  40  engage the roll shaft  26  (see FIG.  18 ). Since the shaft  26  is now supported, the shaft cradles  228  are lowered and the power head  250  is further advanced to press fit the cone  56  of the bearing assembly  38  onto the shaft  26  and to press the cap portion  46  of the roll head  36  into the counterbore  32  of the roll shell  22  (see FIG. 18 a ). The cone or inner race  56  is pushed by a nose  260  of the power head  250  while the cap portion  46  is pushed by a face portion  262  of the power head  250 . The cap portion is pushed until it bottoms out against the counterbore abutments  34 . The bearing cones  56 , however, do not “bottom out” and in fact are pressed short of their theoretically desired locations. The end of the nose  260  which contacts the bearing assembly cone  56  is shortened a predetermined distance to leave a predetermined clearance within the bearing assembly  38  to compensate for manufacturing tolerances and any distortion that is created by later manufacturing operations such as welding. 
     Referring again to FIGS. 9-11, after completion of the operation at the press cap station  168 , the double lift unit  188  is lowered to transfer the roll assembly to the end-most roll cradle  138  on the main shuttle  120  (FIG.  9 ). The main shuttle  120  is indexed a single station and the double lift unit is again raised to locate the roll assembly at the idle station  170  while various assembly and cooling operation are being conducted at the other stations. 
     After completion of those operations, the double lift unit  188  is lowered to again transfer the roll assembly to the end-most roll cradle  138  on the main shuttle  120  (FIG.  10 ). The main shuttle  120  is again indexed to the position shown in FIG.  11  and the double lift unit  188  at the weld stations  172  and  174  is raised to position the roll assembly at the first weld station  172 . 
     Referring to FIG. 9 a , the roll heads  36  of the shaft  26  are clamped between jaws  270 . One set of jaws is mounted on a rotatable shaft  272  and the other jaw  270  is mounted on a rotatable shaft  274  which is driven by a motor  276 . A welding head  277  is positioned at each end of the roll assembly in a position which enables a weld bead  278  to be deposited at the joint between the roll shell  22  and the end cap  36  (FIG.  2 ). 
     Prior to completion of the first welding operation at the weld station  172 , the main shuttle  120  is indexed two positions back to the position illustrated in FIG.  9 . With the main shuttle in this position, the double lift unit  188  at the welding stations  172  and  174  is lowered to deposit the roll assembly on the cradle  138 , which is the third cradle from the right on the main frame  120 , as viewed in FIG.  9 . The main shuttle  120  is then indexed to the position illustrated in FIG. 10 with the workpiece now at the second weld station  174 . 
     The double lift unit is again raised to position the workpiece at the second weld station  174 , which is identical in structure to the station  172 . A second weld bead is applied to the joint between the roll shell  22  and the end cap  46 . The double lift unit  188  is then lowered to redeposit the welded roll assembly on the main shuttle  120  in the position illustrated in FIG.  10 . 
     The main shuttle is indexed to the position illustrated in FIG.  11 . The single left unit  186  at the first cooling station  176  is raised to position the welded workpiece at the cooling station  176 . Cooling water is directed on the ends of the workpiece by spray jets  280 . While the workpiece is at the cooling station  176 , the main shuttle is indexed back to the position illustrated in FIG.  9  and the single lift unit  186  is lowered to deposit the workpiece in the fifth cradle  138  from the right as viewed in FIG.  9 . 
     The main shuttle is indexed to the position shown in FIG.  10  and the single lift unit  186  at the station  178  is raised to position the workpiece at the second cooling station  178 . The second cooling station  178  is identical to the station  176 , and the workpiece is further cooled by the water jets  280  at that station. 
     It should be appreciated that, at this stage of the manufacturing operation, the precise location of the bearing assembly  38  on the shaft  26  for precise axial clearance is necessary because of the pressing, welding and cooling operations. This is particularly true for idler rolls having long shaft lengths, since flexibility and compressibility are directly proportional to shaft length and errors in bearing location are magnified when the bearing is press fit onto such shafts. This invention overcomes these positions by initially press fitting the bearings just short of their theoretically desired locations at the press cap station  168 , as previously described, and then adjusting the bearing to precisely set the axial clearance of the bearing assemblies  38 . The final adjustment of the bearing assemblies is accomplished at the press check station  180 . 
     The workpiece is lowered from its position at the cooling station  178  and the main shuttle  120  is shifted to the position illustrated in FIG.  11 . The single lift unit  186  at the press cap station is raised to position the workpiece at the press check station  180 . 
     Referring now to FIGS. 19-22, the shell  22  is positioned at the press check station by the roll cradles  202  and by a shell clamp  282  which securely retains the shell against a fixed stop plate  284 . The clamp  282  comprises a piston which operates a clamping jaw  286  through a toggle mechanism  288 . An end of the shaft  26  is clamped by a rotatable clamping assembly  290  which is mounted on a table  292  fixed to the moveable frame  106 . The clamping assembly  290  includes a pair of jaws  294  which are adapted to engage the opposed flats  84  at the end of the shaft  26 . Since the flats  84  are positioned with respect to a vertical orientation, it is necessary to turn the shaft  26  to that orientation. A jaw rotating mechanism  294  is adapted to rotate the jaws  294  to a position which aligns the flats  84  in a vertical orientation. 
     With the flats  84  in this orientation, a pair of clamping jaws  296  grip the oriented flats  84  on the other end of the shaft  26 . As may be seen in FIG. 21, the clamping jaws  296  are mounted on a clamping head  298  which in turn is mounted on a side platform  300  (see FIGS.  9  and  19 ). The platform  300  is mounted on slide rails  302  fixed to a table  304  mounted on the stationary frame  104  and is driven by a piston  306  associated with a cylinder  308  having a temposonic transducer on the table  304 . 
     As may be best seen in FIG. 21, the clamping head  298  mounts the jaws  296  by pivot pins  310  and includes a press check shaft  312  which extends through a central opening  314  in the head  298 . The press check shaft  312  is associated with a piston rod  316  of a power cylinder  318  having a temposonic transducer. The jaws  296  are biased apart by tension springs  320  extending between the jaws  296  and the power head  298  and have outer edges which ride on guide rollers  322  mounted on a front crossbeam  324 . The crossbeam  324  is fixed to a pair of guide rods  326  which slidably extend through the head  298 , a pair of guide blocks  328  (see FIG. 20) and are fixed to a rear crossbeam  330 . The crossbeam  330  is engaged by a rod and cylinder unit  332  which moves the rear crossbeam and, therefore, the front crossbeam  324 . Forward movement of the front crossbeam  324  causes the jaws  296  to open and rearward movement of the beam  324  permits the jaws to close against the bias of the springs  320 . 
     After the jaws  294  rotate the flats  84  to a vertical orientation, the jaws release and are retracted to clear the assembly. The clamping jaws  296  then engage the flats  84  on the other end of the shaft and the press check shaft  312  is advanced until a nose  332  of the shaft  312  engages the cone  56  of the bearing assembly  38 . As may be seen in FIG. 21, a bore  334  in the shaft  312  receives the end of the shaft  26  and diametrically opposed slots  336  in the shaft  312  permit the jaws  296  to engage the shaft  26 . A sliding plug  338  biased by a compression spring  340  within the bore  334  engages the end of the shaft  26 . 
     With the shaft  26  gripped in this manner, the piston  308  is activated to cause the platform  300  and, therefore, the shaft  26  to be pushed back and forth. This movement (axial bearing) clearance is recorded by the transducer associated with the piston  308 . Within the power cylinder  318 , with the nose  332  of its associated shaft  312  in contact with the inner bearing race  56 , is an encoder which computes the difference between measured clearance (the degree to which the shaft  26  may be moved back and forth by the piston  308 ) and the desired predetermined clearance. When this distance is computed, the piston  308  and its piston rod  316  causes the nose  332  of the shaft  312  to push the bearing race the computed distance down the shaft  26 . During this operation, the jaws  296  continue to grip the shaft to prevent axial displacement of the shaft  26 . The shaft  26  is again moved back and forth to verify that the bearing clearance is now within the allowable limits. It should be appreciated that during the press check operation that the shaft  26  is subjected to a tensile load for the short distance between the jaws  296  and the bearing race  56  as compared to a compressive load on the entire shaft if the bearings  58  were adjusted to their desired position at the press cap station. 
     During the press check operation, the main shuttle  130  is shifted from the position illustrated in FIG. 11 to the position illustrated in FIG.  9 . After the press check operation, the single lift unit  186  at the press check station is lowered to deposit the finished workpiece in the left end cradle  138  on the main shuttle  120  as viewed in FIG.  9 . The main shuttle  120  is shifted to the position illustrated in FIG. 10 where the completed workpiece is at the unload station  182  having a pair of double left unloaders  350 . One unloader  350  is provided on the stationary frame  104  and another is provided on the moveable frame  106 . 
     The double left unloader  350  has an inclined cradle  352  mounted on a pair of pistons  354  (see FIG.  11 ). With the workpiece positioned at the unload station  182  as shown in FIG. 10, the cradle  352  is raised by the pistons  354  and the completed workpiece may then be removed from the cradle  352 . 
     The workplace is then moved to a lubrication station wherein grease is added to the labyrinth passage  70  and the seals  42  and  44 . Preferably the head assemblies  24  are pregreased prior to the press cap station  104 . From the lubrication station, the assembly is moved to a press station wherein the exterior shields  28  are pressed onto the ends the shaft  26 . Assembly of the idler roll is then complete. 
     While the invention has been described in connection with a particular sequence of assembly operations, those skilled in the art will appreciate that the invention also applies to other sequences. For example, the head assemblies  24  need not be preassembled. The roll end or head  36  may be affixed initially to the shell  22  by welding and the bearing assembly  38  may be press fitted onto the shaft  26  and into the hub portion  48  at the station  168 . The back seal  40  would be installed in the hub portion  48  prior to the press fit operation. Operations at the press check station  180  would be identical to those previously described. 
     It should be further appreciated that joining operations other than welding may be employed to affix the head  36  to the shell  22 . 
     Although particular embodiments of the invention have been described in detail, it will be understood that the invention is not limited correspondingly in scope, but includes all changes and modifications obvious to those skilled in the art.