Abstract:
A adjustable shuttle stop apparatus for use in controlling feeding of material to a machining operation on a machine tool, such as a band saw. The apparatus comprises a feed conveyor, a band saw adjacent to the feed conveyor, a shuttle vise movably disposed on the feed conveyor, and an adjustable stop on the feed conveyor for adjusting a distance between the stop and the shuttle vise and for stopping the shuttle vise at the cutting position. The adjustable stop compensates for undesired movement of the shuttle vise caused by clamping the workpiece such that the distance between the stop and the shuttle vise remains substantially constant. This allows for a consistent cut length of the workpiece on subsequent cutting cycles. Different embodiments of the adjustable stop are disclosed along with a method of use of the apparatus.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to stops used in controlling the feeding of material as a workpiece to a machining operation, such as cutting a length of the material on a band saw, and more particularly, to an adjustable stop which compensates for undesired movement of the workpiece. The stop is illustrated in conjunction with a shuttle vise on a band saw, but the stop may be used in other applications, such as the feeding of material to a punch press, etc. 
     2. Description of the Prior Art 
     Machines for cutting material, such as large band saws which are used to cut workpieces formed of elongated materials, are well known in the art. The workpiece material is positioned on a feed conveyor adjacent to the saw blade and moved into a cutting position under the saw blade by a shuttle vise which is moved to a clamping position to initially clamp the material and then move in a direction toward the saw blade and to a cutting position. A stop is sometimes used to limit movement of the shuttle vise and to insure it stops at the desired cutting position. As the material is moved, it extends beyond the saw blade onto a receiving conveyor where it is clamped by a fixed vise adjacent to the saw blade. At this point, the material is cut by the saw blade. While the saw blade is cutting, the shuttle vise is released from the material and moved back to the desired clamping position to clamp the material again and move it to the cutting position for the next cutting operation. This type of saw works well for many applications where the cut length of the material is not particularly critical. 
     However, in cases where the cut length of the material may be critical this prior art saw may not be able to position the material in the cutting position accurately enough to insure that the cut length is within the desired tolerances. Closer tolerance requirements are becoming more common. The problem has to do with the straightness of the material, surface imperfections, and/or flexibility of the material and the deflection thereof when clamped by the shuttle vise. When the vise clamps the material, the clamping action may actually cause the shuttle vise to move slightly due to these variations in the material. This means that the shuttle vise is moved away from or toward the stop with the result that the cut length of the material may be correspondingly longer or shorter than desired. Obviously, if the movement of the shuttle vise can be greater than the cut length tolerances on the workpiece, this is very undesirable. 
     The present invention solves this problem by providing an adjustable stop to compensate for the amount of undesired movement of the shuttle vise and transmitting a signal to a controller which adjusts the position of the stop. Thus, when the shuttle vise moves to the cutting position and engages the adjusted stop, the cut length of the material will be at the proper length. That is, the adjustment of the stop compensates for the undesired movement of the shuttle vise so that the cut length of the material stays within the desired tolerances. Also, the encoder will detect the incorrect position of the shuttle vise and will adjust the front stop to compensate for the positional error in the shuttle vise. In addition to this positional adjustment, when the shuttle vise clamps the material to be cut, the encoder will detect variances which occur while clamping and will make an adjustment for that error also. 
     It will be understood by those skilled in the art, that this adjustable stop apparatus is useful in any application in which material is clamped and moved. Accordingly, the invention is not intended to be limited to a band saw application. 
     SUMMARY OF THE INVENTION 
     The present invention may be described as a material cutting apparatus comprising a feed conveyor, a band saw adjacent to the feed conveyor, a shuttle vise movably disposed on the feed conveyor and an adjustable stop on the feed conveyor for adjusting a distance between the stop and the shuttle vise. The shuttle vise is adapted for clamping a workpiece on the feed conveyor when in a clamping position and moving the workpiece to a cutting position adjacent to the band saw. The stop is also adapted for stopping the shuttle vise at the cutting position. Preferably, the stop is adapted for adjusting the distance between the stop and shuttle vise in an amount equal to movement of the shuttle vise caused by clamping the workpiece or errors in the initial positioning. 
     The apparatus may further comprise an encoder adapted for generating a signal in response to the movement of the shuttle vise and an actuator for moving the adjustable stop in response to the signal. The apparatus may further comprise a controller for receiving the signal and transmitting this signal to the actuator. 
     The apparatus may additionally comprise a positional sensor for sensing a position of the adjustable stop and transmitting a positional signal in response thereto to the controller. The positional sensor may a transducer, switch or other type of sensor. 
     In one embodiment, the adjustable stop comprises a wedge having an angled face opposite the shuttle vise and an actuator for moving the wedge transversely with respect to the feed conveyor. The actuator is characterized by any linear motion device, such as a pneumatic or hydraulic cylinder. In this first embodiment, the apparatus may further comprise a bumper disposed on the shuttle vise. The bumper has an angled face corresponding to the angled face on the wedge, and movement of the wedge results in varying the distance between the face on the bumper and the face on the wedge. 
     In a second embodiment, the adjustable stop comprises a stepped member having a plurality of faces directed toward the shuttle vise and an actuator for moving the stepped member transversely with respect to the feed conveyor. The actuator may be the same or similar to that described for the first embodiment. In the second embodiment, the apparatus may further comprise a bumper attached to the vise and having a face thereon. The actuator is adapted for moving the stepped member such that a selected one of the plurality of faces is aligned with the face on the bumper. 
     In a third embodiment, the adjustable stop comprises a sleeve, a shaft threadingly connected to the sleeve, and a prime mover for rotating the shaft. The shaft has an end with a face thereon directed toward the shuttle vise. Rotation of the shaft varies the distance between the face and the shuttle vise. The third embodiment may further comprise a bumper attached to the shuttle vise and adapted for engaging the face on the end of the shaft. The prime mover may be directly connected to the shaft or may be connected to the shaft by a drive train such as a first pulley connected to the shaft, a second pulley connected to the prime mover, and a belt interconnecting the first and second pulleys. It will be understood that the adjustable stop mechanism could be mounted on the shuttle vise and the fixed bumper attached to the saw frame. 
     Preferably, in the third embodiment, the apparatus further comprises a spring engaging the shaft and biasing the shaft longitudinally with respect to the sleeve for eliminating play in the threaded connection between the shaft and sleeve. The third embodiment may also comprise a switch and a cam rotatable by the prime mover and having a cam lobe thereon for engaging the switch when the cam is in a predetermined position. This predetermined position preferably corresponds to a longitudinal mid-point of the shaft. The switch is connected to the controller for the shuttle vise so the system can be reset with the location of the shaft known. 
     In a fourth embodiment, the adjustable stop comprises an eccentric cam and a prime mover for rotating the cam. Rotation of the cam varies the distance between the cam surface and the shuttle vise. A bumper may be attached to the shuttle vise and adapted for engaging the cam surface. The prime mover may be directly connected to the cam, such as by a shaft, or may be connected to the cam by a drive train, such as a belt-and-pulley assembly. 
     The present invention may also be described as a method of cutting a workpiece comprising the step of (a) providing a material cutting apparatus comprising a feed conveyor, a band saw adjacent to the feed conveyor, a shuttle vise movably disposed on the feed conveyor, an adapter for clamping a workpiece on the feed conveyor when in a clamping position and moving the workpiece to a cutting position adjacent to the band saw, and a stop on the feed conveyor for stopping the shuttle vise at the cutting position. The method further comprises the steps of (b) detecting movement of the shuttle vise resulting from clamping the workpiece and (c) adjusting the stop on the feed conveyor for compensating for the movement of the shuttle vise such that a distance between the shuttle vise and the stop remains substantially constant. Step (c) may also comprise adjusting the stop for compensating for initial inaccurate positioning of the shuttle vise. 
     Step (c) may comprise generating a signal in response to the movement of the shuttle device and transmitting the signal to an actuator for moving the adjustable stop in response to the signal. 
     In one embodiment, step (c) comprises moving a wedge on the stop transversely with respect to the feed conveyor. In another embodiment, step (c) comprises moving a stepped member having a plurality of faces thereon transversely with respect to the feed conveyor. In still another embodiment, step (c) comprises rotating a shaft connected to the stop. In an additional embodiment, step(c) comprises rotating an eccentric cam to vary the distance between a cam surface on the cam and the shuttle vise. 
     Numerous objects and advantages of the invention will become apparent as the following detailed description of the preferred embodiments is read in conjunction with the drawings which illustrate such embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a side view of the band saw apparatus with adjustable shuttle stop of the present invention. 
     FIG. 2 is a plan view of the apparatus. 
     FIG. 3 is an end view as seen from the feed side of the apparatus. 
     FIG. 4 shows a schematic of the control circuit for the adjustable stop used in the apparatus. 
     FIG. 5 schematically illustrates a first embodiment of the adjustable stop. 
     FIG. 6 is a schematic of a second embodiment of the adjustable stop. 
     FIG. 7 shows a third embodiment of the adjustable stop. 
     FIG. 8 is a view of the adjustable stop as seen from the bottom of FIG.  7 . 
     FIG. 9 illustrates a fourth embodiment of the adjustable stop. 
     FIG. 10 is a plan view of the fourth embodiment. 
     FIG. 11 shows a variation of the first embodiment. 
     FIG. 12 illustrates another variation of the first embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings and more particularly to FIGS. 1-3, the band saw apparatus with adjustable shuttle stop of the present invention is shown and generally designated by the numeral  10 . Apparatus  10  comprises a horizontally disposed feed conveyor  12  and a horizontally disposed receiving conveyor  14 . A band saw  16  is disposed between feed conveyor  12  and receiving conveyor  14  and is adapted for cutting workpiece  18  formed of elongated material. Workpiece  18  includes a single piece or multiple pieces bundled and/or stacked together. Band saw  16  will normally be connected to receiving conveyor  14 . 
     Feed conveyor  12  generally comprises a pair of side rail supports  20  interconnected by a plurality of cross members  22 . Side rail supports  20  are supported on a plurality of legs  24  above a ground surface  26 . 
     Feed conveyor  12  also has a plurality of longitudinally spaced, transversely extending rollers  28  rotatably mounted on a pair of longitudinally extending roller supports  30 . Roller supports  30  are attached to, or integral with, side rail supports  20 . 
     A shuttle vise  32  is mounted on feed conveyor  12  and may be moved longitudinally therealong as will be hereinafter described. 
     As best seen in FIG. 3, shuttle vise  32  comprises an outer housing  34  formed by a pair of upright members  36  and  38  interconnected by a horizontal member  40 . Upright members  36  and  38  are slidably mounted on side rail supports  20  of feed conveyor  12  by a pair of linear guide rail bearings  42 . Each linear bearing  42  includes a rail  44  and a rail bushing  46  movably disposed on the rails. Linear bearings  42  are of a kind known in the art and provide substantially free longitudinal movement of shuttle vise  32  with respect to feed conveyor  12  with relatively little friction. Linear bearings  42  also are designed to resist both horizontal and vertical forces applied by rail bushings  46  on rails  44 . Thus, linear bearings  42  provide a guide for longitudinal movement of shuttle vise  32  and support to resist forces applied to the shuttle vise. 
     In the illustrated embodiment, shuttle vise  32  also comprises a stationary vise plate  48  attached to upright member  36  and a movable vise plate  50  attached to upright member  38  by a vise actuator  52 . Vise actuator  52  may be of any kind known in the art, such as a hydraulic or pneumatic cylinder or other device capable of providing the desired motion. By energizing actuator  52  in a manner known in the art, movable vise plate  50  may be moved in a transverse direction toward or away from stationary vise plate  48 . Alternatively, vise plate  48  may also be movable by an actuator (not shown) similar to actuator  52 . It is not intended that the invention be limited only to a shuttle vise having a movable plate and a stationary plate. Movable vise plate  50  is adapted to engage workpiece  18  and clamp it against stationary vise plate  48  in a manner hereinafter described. 
     A drive mechanism is utilized to move shuttle vise  32  along rails  44  of linear bearings  42 . In the illustrated embodiment, this drive mechanism comprises a driven sprocket  54  mounted at one end of feed conveyor  12 , a drive sprocket  56  mounted at an opposite end of feed conveyor  12 , and a chain  58  wrapped around, and engaged with, the sprockets. As best seen in FIG. 1, chain  58  is connected to one side of shuttle vise  32  at an attachment point  60 , and the other end of the chain is attached to the shuttle vise at another attachment point  62  on the opposite side of the shuttle vise. It will be seen by those skilled in the art that rotation of drive sprocket  56  in a clockwise direction as seen in FIG. 1 will result in a corresponding movement of chain  58  around sprockets  54  and  56  which causes shuttle vise  32  to move to the right toward band saw  16 . Similarly, counterclockwise rotation of driven sprocket  54  will cause the shuttle vise to move away from the band saw. Drive sprocket  56  is actuated by a prime mover  64  of a kind known in the art, such as a reversible electric motor, a servomotor, a hydraulic motor, etc. 
     Other drive mechanisms could also be used. For example, shuttle vise  32  could be driven using a rack and pinion system, a hydraulic or pneumatic cylinder, a rotating screw device, etc. 
     An encoder strip  67  is attached to one of side rail supports  20  of feed conveyor  12  adjacent to one of rails  44 , as seen in FIG.  2 . An encoder reader  68  is attached to shuttle vise  32  and adapted to read encoder strip  67  as the shuttle vise is moved along feed conveyor  12 . As will be further described herein, encoder reader  68  generates an encoder signal in response to the movement. 
     In an alternate embodiment, also shown in FIG. 2 as well as FIGS. 1 and 4, a belt  66  is attached to shuttle vise  32 , and the belt engages belt pulleys  69  and  71 . An encoder  68 ′ is used to measure the rotation of belt pulley  69  corresponding to the movement of belt  66 , and thus of shuttle vise  32 . As will be further described herein in this embodiment, encoder  68 ′ generates an encoder signal in response to the movement. 
     Alternatively, other methods of measuring the movement of shuttle vise  32  may be used. For example, measurement could be by use of a laser, using an encoder to measure rotation of a pinion gear on a rack attached to the shuttle vise, etc. 
     Receiving conveyor  14  comprises a pair of side supports  80  interconnected by cross members  82 . Side supports  80  are supported on ground surface  26  by a plurality of legs  84 . 
     Receiving conveyor  14  also includes a plurality of longitudinally spaced transverse rollers  86  rotatably mounted on a pair of longitudinally extending roller supports  88 . Roller supports  88  are attached to, or integral with, the corresponding cross members  82 . 
     Band saw  16  comprises an outer housing  90  which contains a rotating band saw blade  92  and band saw driver  94  therein. Band saw driver  94  is of a kind known in the art, such as an electric motor. Band saw portion  16  is mounted such that band saw blade  92  may be moved downwardly so that it cuts through workpiece  18  when the workpiece is at the cutting position thereof. Again, the invention is not intended to be limited to the particular band saw embodiment shown. 
     A fixed vise  96  is positioned adjacent to the inlet side of band saw  16  and is of construction similar to shuttle vise  32  except that the fixed vise does not move. Fixed vise  96  has an outer housing  98  with a stationary vise plate  100  attached to the housing and a movable vise plate  102  connected to the housing by a vise actuator  104 . Vise actuator  104  is similar to previously described vise actuator  52  and, when energized, may be used to position movable vise plate  102  toward and away from stationary vise plate  100 . Alternately, two movable vise plates could be utilized. 
     Similarly, another fixed vise  97  may be located adjacent to the discharge side of band saw  16 . Fixed vise  97  has an outer housing  99  with a stationary vise plate  101  attached to the housing and a movable vise plate  103  connected to the housing by a vise actuator  105 . Vise actuator  105  is similar to previously described vise actuator  104  and, when energized, may be used to position movable vise plate  103  toward and away from stationary vise plate  101 . Optionally, two moveable vise plates could be used. 
     Apparatus  10  as previously described is of a kind generally known in the art, such as that disclosed in U.S. Pat. No. 5,353,910, a copy of which is incorporated herein by reference. 
     Apparatus  10  further comprises an adjustable stop  110  for limiting the movement of shuttle vise  32  toward band saw  16  when moving workpiece  18  to the cutting position. Shuttle vise  32  stops moving toward band saw portion  16  when bumper  112  on the shuttle vise engages adjustable stop  110 . 
     Referring now to FIG. 4, a control circuit for adjustable stop  110  and shuttle vise  32  is shown. Shuttle vise  32  is driven as previously described by prime mover  64 . The movement of shuttle vise  32 , and the corresponding movement of encoder strip  66 , results in encoder  68  precisely locating the position of shuttle vise  32  and sending a signal in response to that position to a controller  114 . Controller  114  sends a signal to a stop actuator  116  which controls movement of adjustable stop  110  toward and away from shuttle vise  32 . 
     As will be further described herein, adjusting stop  110  to compensate for errors in positioning and/or movement caused by clamping, speeds up positioning time for shuttle vise  32 . Adjustable stop  110  makes fine adjustments easier than the more coarse general positioning of shuttle vise  32  as well as providing adjustment after clamping workpiece  18 . 
     In operation, workpiece  18  is positioned on feed conveyor  12  such that it may be engaged by shuttle vise  32 . As previously stated, workpiece  18  may include a plurality of elongated items, such as pieces of steel bar stock. Shuttle vise  32  moves away from band saw  16  until it reaches the desired clamping position which is predetermined, based upon the desired cut length of workpiece  18 . Vise actuator  52  is energized so that movable vise plate  50  is moved toward stationary vise plate  48  to clampingly engage workpiece  18  between the vise plates. As previously mentioned, the action of clamping workpiece  18  may cause shuttle vise  32  to move somewhat from its original, predetermined clamping position. Because the material of workpiece  18  may not be straight, may have surface imperfections, or may compress or flex during clamping, the reaction forces thus applied to shuttle vise  32 , and the tolerances of all of the components, can result in the shuttle vise moving from the optimum position thereof. 
     After clamping, shuttle vise  32  is moved toward band saw  16  until it engages stop  110  at the cutting position. If stop  110  is fixed, any movement of shuttle vise  32  caused by the clamping on workpiece  18  will result in the overall movement of the shuttle vise to be something other than what is desired. This is a particular problem, if the undesired movement of shuttle vise  32  during the clamping operation results in a change which is outside the tolerance of the cut length of workpiece  18 . That is, if shuttle vise  32  is moved away from band saw  16  and away from a fixed stop, the cut length of the material will be greater than desired. Similarly, if shuttle vise  32  is moved toward band saw portion  16  during clamping, the resulting movement toward a fixed stop would cause the workpiece to be cut shorter than desired. 
     Because of the nature of the materials clamped, it is virtually impossible to prevent this type of movement of shuttle vise  32 . 
     Adjustable stop  110  eliminates this problem. When shuttle vise  32  is moved to its clamping position in a direction away from band saw portion  16 , this movement is measured by encoder  68 . After clamping, the additional movement of shuttle vise  32  is also detected by encoder  68 . Encoder  68  sends a signal to controller  114  which in turn energizes stop actuator  116  to move adjustable stop  110  to a distance equal to, and in the same direction as, the movement of shuttle vise  32  during clamping. That is, if the clamping causes shuttle vise  32  to be moved back from its desired position by 0.060 inches, stop actuator  116  will move adjustable stop  110  away from band saw  16  and toward shuttle vise  32  by the same distance. Thus, when shuttle  32  is then moved from the clamping position to the cutting position, it will move the original, predetermined distance. Thus, there has been compensation for the undesired movement during clamping. This compensation by adjustable stop  110  provides that the cut lengths of workpiece  18  are substantially the same for each cycle. In this way, much more precise cut length tolerances can be met using apparatus  10  than with previously known band saws. 
     Also, controller  114  receives a positional signal from a positional sensor  117  in response to the current position of stop actuator  116  and/or adjustable stop  110 . Sensor  117  may be a transducer or other sensor if a kind known in the art. It can even be a switch triggered by movement of adjustable stop  110 . Sensor  117  and the positional signal therefrom are used to control movement of shuttle vise  32  in order to maximize the available adjustable movement of adjustable stop  110 . For example, if adjustable stop  110  were in an extended position, controller  114  would control the initial movement of shuttle vise  32  to stop the shuttle vise such that it requires adjustable stop  110  to retract for the correct length, and vice versa. Alternatively, adjustable stop  110  can automatically be reset to a mid-position whenever shuttle vise  32  is moved to its clamping position. The various embodiments discussed herein explain this further. 
     Referring now to FIGS. 5-10, specific embodiments of adjustable stop  110  are shown and generally designated by the numerals  110 A,  110 B,  110 C and  110 D. While four embodiments of adjustable stop  110  are shown, the invention is not intended to be limited only to these four. 
     Referring now to FIG. 5, a first embodiment adjustable stop  110 A is shown. In this embodiment, shuttle vise  32  has a first embodiment bumper  112 A thereon. Bumper  112 A has a face  118  which is angled from a transverse plane with respect to apparatus  10 . Adjustable stop  110 A comprises a wedge supported for transverse movement on a support  122 . Wedge  120  is connected to a first embodiment stop actuator  116 A. Stop actuator  116 A is illustrated as a pressure-actuated hydraulic or pneumatic cylinder, but any other linear motion device providing linear movement of stop  110 A would be acceptable, as will be further described herein. 
     Wedge  120  has a face  124  which is angled to correspond to face  118  on bumper  112 A. 
     Undesired movement of shuttle vise  32  upon clamping is detected by encoder  68  which sends a signal to stop actuator  116 A to move wedge  120  transversely with respect to feed conveyor  12  along support  122 . By moving wedge  120  to the left as shown in FIG. 5, the point of contact on face  124  is moved closer to face  118 , and conversely, moving wedge  120  to the right in FIG. 5 will move face  124  away from face  118 . The amount of movement of stop actuator  116  is determined by controller  114  so that the distance between faces  124  and  118  is moved by the same amount, and in the same direction as, the undesired movement of shuttle vise  32  during clamping. 
     Sensor  117 A sends a positional signal to controller  114  to control movement of shuttle vise  32  in order to maximize the available adjustable movement of adjustable stop  110 A as previously described generally in the discussion of FIG.  4 . 
     FIG. 6 shows a second embodiment adjustable stop  110 B which is somewhat similar to first embodiment  110 A. In second embodiment  110 B, shuttle vise  32  has a second embodiment bumper  112 B having a transversely extending face  126  thereon. Adjustable stop  110 B includes a stepped member  128  supported on a support  130  and actuated by a second embodiment stop actuator  116 B. Stop actuator  116 B is essentially the same as first embodiment stop actuator  116 A and may comprise a hydraulic or pneumatic cylinder or other linear movement device. 
     Stepped member  128  has a plurality of stepped surfaces, such as  132 ,  134  and  136  thereon. While three such stepped surfaces are shown in FIG. 6, it will be understood by those skilled in the art that more or less stepped surfaces could be utilized depending on circumstances. When stop actuator  116 B is actuated to locate face  132  opposite bumper  112 B, the distance between faces  126  and  132  will be less than between faces  126  and  134 . Additionally, the distance between faces  126  and  134  will be less than between faces  126  and  136 . By energizing stop actuator  116 B in response to a signal from controller  114 , the desired face  132 ,  134  or  136  is positioned opposite face  126  to compensate for movement of shuttle vise  32  when clamping. 
     Sensor  117 B sends a positional signal to controller  114  to control movement of shuttle vise  32  in order to maximize the available adjustable movement of adjustable stop  110 B as previously described generally in the discussion of FIG.  4 . 
     Referring now to FIGS. 7 and 8, a third embodiment adjustable stop  110 C is illustrated in which shuttle vise  32  has a bumper  112 C thereon with a face  138  extending transversely. Third embodiment stop  110 C comprises a mount  140  with an internally threaded sleeve  142 , such as an Acme nut, attached thereto. Mount  140  may be attached to fixed object such as one of side rail supports  20  of feed conveyor  12  (not shown in FIGS.  7  and  8 ). A shaft  144  is threadingly engaged with sleeve  142  and has an end face  146  thereon generally opposite face  138  on bumper  112 C. As illustrated, third embodiment stop actuator  116 C comprises a pulley assembly with a pulley  148  which is connected to another pulley  150  by a drive belt  152 . Pulley  150  is attached to a shaft  154  of a prime mover  156 , also part of stop actuator  116 C, and driven by shaft  154  in response to a signal from controller  114 . Thus, when shuttle vise  32  moves undesirably during clamping, prime mover  156  is actuated in response to that movement. Prime mover  156  is of a type which is reversible, such as a reversible electric motor, a servomotor, hydraulic pump, etc. Actuation of prime mover  156  results in corresponding rotation of pulleys  150  and  148  through drive belt  152 . This rotates shaft  144  within sleeve  142  which in turn causes longitudinal movement of shaft  144  and end face  146  toward or away from face  138 . In this way, the distance between faces  138  and  144  may be adjusted to correspond with the clamping movement of shuttle vise  32 . The total longitudinal movement of shaft  144  is on the order of about 0.1 inches which is not enough to cause any significant alignment problems of pulley  148  with respect to pulley  150 . 
     A spring  158  is attached to mount  140  by any means know in the art. Spring  158  has a cantilevered spring arm  160  which engages a groove  162  in a distal end of shaft  144 . Spring arm  160  is preloaded to always bias shaft  144  in a direction indicated by arrow  164  regardless of the longitudinal position of the shaft. This biasing of shaft  144  insures that any slack or “play” in the threaded engagement of the shaft with sleeve  142  is eliminated and therefore does not affect the longitudinal positioning of shaft  144 . 
     A cam  166  is connected to shaft  154  of prime mover  156  on the outside of pulley  150 . Cam  166  has a cam lobe  168  thereon adapted for engaging sensor  117 C, such as a switch  170 . Switch  170  is of a kind known the art and is connected to controller  114 , but other types of sensors could be used. Preferably, cam lobe  168  engages switch  170 , as seen in FIG. 8, when shaft  144  is approximately at its mid-point longitudinally. In this way, controller  114  can easily be reset and recalibrated when shaft  144  is not positioned too far in either longitudinal direction thereof. Thus, switch  170  acts as another embodiment of sensor  117  as generally illustrated in FIG.  4 . 
     Alternatively, shaft  144  could be directly coupled to the shaft of a prime mover which may be any type of device which provides reversible rotational movement. 
     Finally, referring to FIGS. 9 and 10, a fourth embodiment adjustable stop  110 D is shown in which shuttle vise  32  has a bumper  112 D thereon with a face  172  extending transversely. Fourth embodiment stop  110 D comprises an eccentric cam  174  driven by fourth embodiment stop actuator  116 D through a shaft  176 . Stop actuator  116 D could also be connected to cam  174  by a belt-and-pulley assembly in a manner known in the art. Fourth embodiment stop actuator  116 D is preferably a prime mover, such as a reversible step motor which allows rotation of cam  174  in either direction in variable increments, although other rotatable devices could also be used. Cam  174  has an outer cam surface  178  thereon which is adapted for contacting face  172  on bumper  112 D. By rotation of cam  174 , it will be seen by those skilled in the art that the distance between the center of shaft  176  and the point of contact of cam surface  178  with face  172  may be varied to adjust the position of shuttle vise  32 . 
     Sensor  117 D sends a positional signal to controller  114  related to the rotational position of shaft  176  and/or cam  174  to control movement of shuttle vise  32  in order to maximize the available adjustable movement of adjustable stop  110 D as previously described generally in the discussion of FIG.  4 . 
     Referring now to FIGS. 11 and 12, two variations of first embodiment adjustable stop  110 A are shown. It will be seen by those skilled in the art that these variations may be incorporated in other embodiments in addition to the first embodiment. 
     In FIG. 11, a stop actuator  116 A′ is shown as a reversible step motor or the like connected to wedge  120  by a screw member which results in linear movement of the wedge as the motor is rotated. 
     In FIG. 12, linear motion of wedge  120  is provided by a rack and pinion gear system. A pinion gear  182  is connected to a stop actuator  116 A″ by a shaft  184 . Pinion gear  182  engages a gear rack  186  which is connected to wedge  120 . This, of course, results in linear movement of rack  186  and wedge  120  in response to rotation of pinion gear  182 . Stop actuator  116 A″ is shown as a prime mover, such as a reversible step motor, but other rotatable devices could also be used. 
     It will be seen, therefore, that the band saw with adjustable shuttle stop of the present invention is well adapted to carry out the ends and advantages mentioned, as well as those inherent therein. While presently preferred embodiments of the apparatus have been shown for the purposes of this disclosure, numerous changes in the arrangement and construction of parts may be made by those skilled in the art. All such changes are encompassed within the scope and spirit of the appended claims.