Abstract:
A manually operated pallet changer system for use with automatic machine tools includes a pallet changer and a compatible machine tool mounted pallet receiver. The pallet changer includes a massive, floor supported base to which a cantilevered first platform is pivotally attached for rotation between a pallet-exchange position and a work-setup position. A second platform rests atop the first platform and supports a pair of work pallet guides. The two platforms are rotatably attached near their centers so that the pallet guides can be interchanged by rotating the upper platform about its center by 180°. The configuration permits the platforms to be rotated as a unit away from a machine tool to the work-setup position. Work pallets are assembled and then the platforms are rotated together into the pallet-exchange position in which one of the pallet guides is aligned for transferring a work pallet to the machine tool mounted pallet receiver. The receiver includes an air bearing upper surface for simplifying the movement and positioning of a work pallet, a deployable clamping plate, and a pair of retractable locating pins for engaging openings on the underside of a work pallet to insure precision alignment during a machining operation.

Description:
BACKGROUND 
     1. Field of the Invention 
     The invention relates to a work pallet changer, and in particular to a manually operated work pallet changer system. 
     2. Background of the Invention 
     In machine shops using large, expensive automatic machine tools, such as the Vertical Machining Center, the Horizontal Machine Center, and Drilling and Tapping machines, it is desirable to keep the machine tool busy in order to make it an effective and efficient investment. Many machine shops have adopted the use of work pallet changers also known as pallet indexers. The use of a pallet indexer permits a machine tool operator to assemble the work on portable pallets and to efficiently move the work to and from a machine tool work table by transferring assembled work pallets. This procedure avoids unnecessary downtime otherwise required to setup and teardown the work directly on the work table. 
     Using such an indexer, a new work pallet is setup off line while the machining proceeds on a previously assembled work pallet. The indexer is then used to quickly remove a pallet and its completed work from the machine tool and to replace it with the newly setup work pallet. The machine tool is inoperative only during the short time required to exchange the work pallets. In this way the machine tool is kept busy, and the owner&#39;s investment is maximized. 
     A variety of devices and methods have been proposed for this purpose. Among these devices are a class of pallet indexers which operate on a shuttle or side-by-side principle, as for example the pallet changer illustrated in U.S. Pat. No. 5,156,254. Another popular class of pallet indexers uses a rotary or carousel principle, as illustrated for example in U.S. Pat. No. 5,018,617. 
     Some indexers are manually operated, while many others are semi-automatic or even fully automatic in operation. Though these pallet indexers achieve the goal of keeping the machine tool busy, they tend to suffer from two major problems which undermine the goal of maximizing the owner&#39;s investment. 
     The first problem relates to the manner in which the side-to-side indexers interfere with a machine tool operator&#39;s ability to physically monitor the work in progress. These shuttle-type indexers often include a portion connecting two side units. That portion extends outwardly from the machine tool near a position at which the machine tool operator must stand in order to effectively observe and monitor the machining operation. In such cases, the machine tool operator must lean across this connecting portion in order to observe and listen to the work as it proceeds. Though it is possible for the machinist to work in this manner, the leaning-across increases fatigue and interferes with both his efficiency and his ability to use skills effectively to insure the machining is properly carried out. This shortcoming tends to be present in both the manually operated and the automatic indexers of the side-to-side configuration. 
     The second common problem relates to the complexity of the automatic and the semi-automatic indexers, and even many of the manually operated devices. These indexers are expensive to purchase and are often costly to maintain. What is gained in efficient machine shop operation, is lost in an increased, and often hidden cost for indexer maintenance and repair. As a result, the apparent savings are somewhat illusory, particularly in the smaller and mid-sized machine shop. 
     It would be desirable to provide a work pallet changer that is relatively inexpensive to purchase, that provides an increase in productivity by being easy to operate, that is configured to permit the machine tool operator to monitor the work without undue fatigue, and which presents the shop owner with few hidden costs related to upkeep. 
     SUMMARY OF THE INVENTION 
     The present invention meets these requirements by providing a manually operated work pallet changer providing simple handling for a pair of work pallets. The pallet changer is inexpensive, is easy to install and to adjust, is easily maintained, and rotates out of the machinist&#39;s way once a work pallet exchange is completed. 
     In a specific embodiment of one aspect of the invention, a manually operated work pallet changer includes a heavy, floor supported base. A horizontal platform is pivotally attached to the base, and defines a primary vertical axis extending through the center of the base. The horizontal platform rotates, with respect to the base and the primary axis, between a work pallet-setup position and a work pallet-exchange position. The horizontal platform extends outwardly from the primary axis in cantilever fashion. The outwardly extending portion of the platform includes a bearing which defines a second vertical axis parallel to the primary axis. A generally rectangular pallet guide platform is rotatably attached at the bearing, above and parallel to the horizontal platform, and is thus able to rotate around the secondary axis. A pair of work pallet guides are aligned in opposite directions on top of the pallet guide platform. 
     Rotation of the pallet guide platform about the secondary axis by 180° brings first one and then the other work pallet guide into the work pallet-exchange position. Pivoting the horizontal platform around the primary axis shifts the pallet guide platform between the work pallet-exchange position and the work pallet-setup position, away from the machine tool. 
     In a specific embodiment of another aspect of the invention, an air-bearing work pallet receiver includes a planar top surface having a plurality of small openings connected through an automatic valve to a compressed gas. When the valve is opened, the gas is ejected through the small openings, forming an air-bearing surface which floats the heavy work pallets and facilitates their movement and careful alignment on the machine tool. The receiver also includes a deployable clamping plate which mates with a congruent opening formed on the underside of the work pallet. Once the deployed clamping plate has engaged the opening, the work pallet is retained against the lift of the air-bearing and is coarsely aligned atop the work pallet receiver. Finally, the receiver includes a pair of retractable locating pins which are withdrawn below the air-bearing surface while a work pallet is being moved and adjusted, and which are then extended into corresponding openings on the underside of the work pallet providing a precise and repeatable alignment during the machining operations. The clamping plate is then moved from a deployed receiving position to a work pallet clamping position. 
     In another embodiment of the invention, a manually operated work pallet changer system includes a pallet changer and an air-bearing work pallet receiver, as described above. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a further understanding of the objects, features and advantages of the work pallet changer system, reference should be had to the following description of the preferred embodiment, taken in conjunction with the accompanying drawing, in which like parts are given like reference numerals and wherein: 
     FIG. 1 is an exploded perspective view of a preferred embodiment of the manually operated pallet changer in accordance with one aspect of the present invention. 
     FIG. 2 is a partial perspective view illustrating use of a temporary guide bridge for transferring a work pallet between the manually operated pallet changer of FIG. 1 and a machine tool mounted work pallet receiver. 
     FIG. 3 is a top perspective view of a preferred embodiment of a work pallet receiver having an air-bearing surface, a deployable clamping plate, a pair of retractable locating pins, and an attached guide bridge assembly. 
     FIG. 4A is a plan view showing the pallet changer of FIG. 1 rotated into a pallets exchange position. 
     FIG. 4B is a plan view showing the pallet changer in a work-setup position and the upper pallet guide member being rotated by 180° to exchange pallet guides. 
     FIG. 5 is a side view of an alternative embodiment of the work pallet changer adapted for mounting on the side of a machine tool. 
     FIG. 6A is a schematic diagram illustrating the use of a valve to activate the air-bearing surface and to retract the locating pins of the work pallet receiver of FIG.  3 . 
     FIG. 6B is a schematic diagram illustrating the valve operated to deploy the locating pins and to deactivate the air-bearing surface. 
     FIG. 7 is a cutaway end view illustrating a locating pin in a recess on the underside of a work pallet. 
     FIG. 8 is an end view illustrating detail of a deployable clamping plate and a conforming clamping slot. 
     FIG. 9 is a schematic diagram illustrating an apparatus for deploying a clamping plate in a vertical direction. 
     FIG. 10 is a partial plan view showing a rectangular static base member using corner placement of a primary index axis. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     With respect to FIG. 1 there is shown an exploded, perspective view of a manually operated work pallet changer according to a preferred embodiment of one aspect of the present invention. The manually operated pallet changer is designated generally by the numeral  10  and includes a static base mount  12 , a pivoting base member  14 , a primary support member  16 , a guide support member  18 , and a pair of work pallet guides  20  and  22 . 
     The static base mount  12  is a massive support intended to rest upon a floor and to provide stability for the pallet changer  10 . The static base mount  12  includes an upwardly extending shaft  24  for rotationally supporting the pivoting base member  14 . Bearings (not shown) are located within the pivoting base member  14  for permitting rotation about the shaft  24  and defining a primary index axis  26  which is essentially vertical. 
     In a specific embodiment of the pallet changer  10 , the static base mount  12  is circular at the base, having a diameter of 24 inches. The static base mount  12  weighs approximately 100 pounds. The upwardly extending shaft  24  has a diameter of approximately 2.25 inches, and the bearings (not shown) which connect the pivoting base member  14  to the shaft  24  are two tapered roller bearings, one near the lower end of the shaft  24 , the other near the upper end, and providing both thrust and radial stability. 
     The primary support member  16  is essentially a square platform rigidly attached to an upper end of the rotating base member  14  and extending outwardly from the primary index axis  26 . In a specific embodiment, the primary support member  16  measures  24  by 31 inches and is made of ⅝ inch drawn aluminum stock. The combination of the pivoting base member  14  and the primary support member  16  is sufficiently rigid to maintain the outwardly extending portion in a generally horizontal plane. In one alternative embodiment, a brace member extends between a lower portion of the pivoting base member  14  and the outwardly extending portion of the primary support member  16  (see FIG.  5 ). 
     A bearing  28  is located near the center of the primary support member  16  and defines a secondary axis  30  parallel to the primary index axis  26 . In one embodiment, the bearing  28  is a tapered roller bearing of approximately 2 inch diameter. A series of horizontal load bearing members  32  are arranged in a circle surrounding and set apart from the bearing  28  on an upper surface  33  of the primary support member  16 . In a specific embodiment, the load bearing members  32  are polyurethane caster wheels on steel axles. Eight such members  32  are disposed in a circle of about 20″ diameter, centered around the bearing  28  and sitting in wells in the surface  33 . 
     The guide support member  18  conforms in shape to the primary support member  16  and rests on top of the horizontal bearing members  32 . The guide support member  18  is attached near its center to the bearing  28  so that the guide support member  18  is free to rotate in a horizontal plane about the secondary axis  30 . The pair of work pallet guides  20  and  22  are aligned near opposed corners  34 ,  36  of an upper surface  38  of the guide support member  18 . In a specific embodiment, the guide support member  18  measures 31 inches by 31 inches and is made of ⅝ inch drawn aluminum stock. 
     In general use, the static base mount  12  of the manually operated work pallet changer  10  is positioned on the floor near the work station of an automatic machine tool (not shown). The guide support member  18 , and the primary support member  16  are rotated as a single unit about the primary index axis  26  between a pallet-exchange position near the machine tool, and a work-setup position away from the machine tool. In use, a pair of assembled work pallets waiting to be machined (not shown) are located one on each work pallet guide  20 ,  22 . At the work-setup position, the guide support member  18  and the work pallet guides  20 ,  22  are rotated 180° about the secondary axis  30  to exchange the relative positions of the opposed work pallet guides. 
     FIG. 2 is a partial, perspective view illustrating an exchange of a work pallet  40  between the manually operated pallet changer  10  and an automatic machine tool, which is designated generally by the numeral  42 . An air-bearing work pallet receiver  44  is located at a work station atop the machine tool  42 , and receives and clamps the work pallet  40  in place throughout the machining operations. In the illustrated embodiment, a short pallet guide bridge  46  is used to temporarily connect the pallet changer  10  with the work pallet receiver  44  during the work pallet transfer. The work pallet  40  is machined from type MIC-6 aluminum micro casting, available from Alcoa and Reynolds. The finished work pallet  40  measures 20 inches wide by 16 inches deep by 1.25 inch thick. 
     The work pallet receiver  44  includes a T-shaped deployable clamping plate  47  which engages a conforming clamping slot  48  formed on the underside of the work pallet  40  as the work pallet  40  moves across the guide bridge  46  and onto the work pallet receiver  44 . The clamping slot  48  is formed on the underside of the work pallet  40  by machining, and the micro-cast aluminum is preferred because of its ability to maintain its flatness after the clamping slot  48  has been machined into its bottom side. During the work pallet transfer from the pallet changer  10  to the machine tool  42 , the cooperation of the deployable clamping plate  47  with the conforming clamping slot  48  guides the work pallet  40  into position atop the work pallet receiver  44 . 
     During the transfer, a compressed gas is inserted through a pipe  50  into a cavity (not shown) within the body of the work pallet receiver  44 . The compressed gas is ejected through a plurality of small holes  52  located in an upper surface  53  of the work pallet receiver  44  creating an air-bearing for easing the movement of the heavy work pallet  40  during the transfer (an assembled work pallet may weigh as much as 200 pounds). In a specific embodiment, the compressed gas is air under 100 pounds pressure. The small holes are 0.050 inch in diameter and a typical air-bearing surface includes approximately 16 to 20 such holes. The surface  53  is generally planar. 
     The work pallet receiver  44  also includes a pair of retractable locating pins  54 , located near opposite corners. These locating pins are retracted below the air-bearing surface  53  during a work pallet transfer and then are raised into corresponding openings which are formed in the lower surface of the work pallet  40  and provide a positive locating reference with respect to the defined machine tool work station. In a specific embodiment, the locating pins  54  are stainless steel, approximately 0.75 inch in diameter and extending approximately 0.75 inch above the surface  53  when fully deployed. 
     FIG. 3 is a perspective top view of a preferred embodiment of a work pallet receiver, designated generally by the numeral  51 . The preferred work pallet receiver  51  differs slightly from the work pallet receiver illustrated in FIG.  2 . In addition to the receiver  44 , the air-bearing surface  53 , the clamping plate  46 , and the retractable locating pins  54 , shown in a deployed position extending above the air-bearing surface  53 , the preferred work pallet receiver  51  includes a guide bridge  55  having one end  57  permanently attached to a forward end  59  of the receiver  44 . The attached guide bridge  55  includes a plurality of roller-type guide bearing members  61  made of 0.75 inch aluminum rods supported in polyurethane bushings at 2 inch centers. The same construction is used for the pallet guides  20 ,  22  of FIG.  1 . 
     When the preferred work pallet receiver  51  is used with the manually operated work pallet changer  10 , forming a work pallet changer system, the temporary bridge  46  of FIG. 2 is not required. Instead, the permanently attached bridge  55  extends from the air-bearing surface  53  and the forward end  59  to a forward edge of the machine tool  42 . The static base mount  12  (FIG. 1) of the manually operated work pallet changer  10  is positioned such that the primary and guide support members  16 ,  18  (FIG. 2) can be rotated to bring one work pallet guide  22  (FIG. 2) into close proximity with the receiver guide bridge  55 . The assembled work pallet  40  (FIG. 2) is then moved by hand along the work pallet guide  22  and onto the receiver guide bridge  55  (FIG. 3) and finally onto the air-bearing surface  53  for engagement with the deployable clamping plate  47 . 
     In a preferred embodiment, the receiver guide bridge  55  does not extend beyond a front edge of the machine tool  42  into a space normally occupied by the machinist, and thus does not interfere with his monitoring of the machining operation. The advantage of the permanently attached guide bridge  55  of FIG. 3 over the temporary guide bridge  46  of FIG. 2 is that the attached guide bridge does not require a separate place for storage when not in use, and is less likely to become lost or damaged. 
     FIGS. 4A and 4B are plan views illustrating the exchange (FIG. 4A) and the setup (FIG. 4B) positions, respectively, of the manually operated work pallet changer  10 . 
     FIG. 4A illustrates the work pallet changer  10  located adjacent the machine tool  42  so that the pallet guide  22  is aligned with the work pallet receiver  44 . The primary support member  16  and the guide support member  18  are aligned with each other so that their square shapes are congruent and are rotated into the exchange position so that the pallet guide  22  is aligned with the work pallet receiver  44 . A portion of the static base mount  12  extends beyond the support members  16 ,  18 , and is located close to the machine tool  42  and to the left side of the work pallet receiver  44 . A work pallet  40  is shown located on the pallet guide  22  and the temporary pallet guide bridge  46  connects between one end of the pallet guide  22  and the work pallet receiver  44 . In this exchange position, the work pallet  40  can be manually shifted along the pallet guide  22  and the temporary guide bridge  46  onto the air-bearing surface of the work pallet receiver  44 . The locating pins  54  are in the retracted position, and the clamping plate  47  is deployed into a receiving position. A second work pallet  56  is located on the pallet guide  20 . 
     FIG. 4B illustrates the work pallet changer  10  with the primary support member  16  rotated approximately 60° in a clockwise direction away from the machine tool  42  and into a setup position. The guide support member  18  has been rotated approximately an additional 100° in the clockwise direction. The work pallet  40  has been transferred from the pallet guide  22  to the work pallet receiver  44 . A machine tool operator  58  is now able to stand in the space between the rotated primary support member  16  and the machine tool  42 , permitting the operator to closely observe the machine tool operation. 
     FIG. 5 is a side view illustrating an alternative embodiment of a manually operated work pallet changer, designated generally by the numeral  60 . The pallet changer  60  includes a static machine mount  62  which is attached to one side of an automatic machine tool  64 . A rotating base member  66  is pivotally attached to the static machine mount  62 , defining a primary index axis  68 . A primary support member  70  is connected to an upper end  72  of the rotating base member  66 . A brace  74  extends between a lower end  76  of the rotating base member  66  and an outwardly extending portion  78  of the primary support member  70 . In all other respects, the pallet changer  60  is essentially the equivalent of the preferred embodiment illustrated in FIG.  1 . 
     FIGS. 6A and 6B are schematic diagrams illustrating the use of a valve and a compressed gas to retract and deploy the retractable locating pins and to activate and deactivate the air-bearing surface. 
     FIG. 6A includes a cross-sectional portion  82  of the work pallet, a locating pin  84  having a piston portion  85 , a valve  86 , a compressed gas  88  emitting from a plurality of small openings, an air-bearing surface  89 , a piston chamber  90 , a compressed gas source line  92 , a compressed gas activation line  94 , and an air-bearing chamber  96 . 
     When the valve  86  is rotated into the position shown, the compressed gas at the source line  92  is permitted to pass into the activation line  94  and moves into the chamber  90  above the piston  85 , and into the chamber  96 , emitting from the small openings  88  to create an air-bearing surface  89 . The piston  85  is driven toward the lower end of the chamber  90  causing the attached locating pin  84  to retract into the work pallet receiver  82 . 
     FIG. 6B, the valve  86  has been rotated so that the compressed gas in the source line  92  is disconnected from the activation line  94  and is connected to a deploy line  98 . The gas moves via line  98  into the chamber  90  below the piston  85 , urging the piston  85  toward an upper end of the chamber  90  and extending the attached locating pin  84  above the surface  89  of the work pallet receiver  82 . 
     FIG. 7 is a cutaway end view showing the engagement of a deployed locating pin  54  within a compatible recess  63  in the underside of a work pallet  40 . The locating pin  54  extends above the planar surface  53  of the work pallet receiver  44 . 
     FIG. 8 is an end view of a work pallet receiver  44  and a work pallet  40 , illustrating engagement of the T-shaped deployable clamping plate  47  within the conforming clamping slot  48  on the underside of the work pallet  40 . An overhanging ledge  100  of the deployable clamping plate  47  mates with a conforming undercut lip  102  of the clamping slot  48 . The clamping plate  47  is movable a short distance both upward and downward in the vertical direction as indicated by the arrow  108 . 
     When moved upward to the full extent of its short range of vertical motion, the clamping plate  47  defines a “receiving” position (also referred to as “open” and “unlocked” position). In the receiving position, the clamping plate  47  does not interfere with the conforming clamping slot  48 , permitting the work pallet  40  to be moved easily onto and off of the work pallet receiver  44 . When the air-bearing is activated, lifting the work pallet  40 , the ledge  100  and the lip  102  cooperate to retain the work pallet  40  against the lifting force of the air-bearing. 
     When the clamping plate  47  is moved downward to the full extent of its vertical motion, the ledge  100  acts upon the lip  102 , forcing the work pallet  40  down against the planar surface  53  of the work pallet receiver  44 . This full downward position of the clamping plate  47  defines a “locked” (also “clamped”) position. In the locked position, the work pallet  40  is locked against the planar surface  53  and does not move. Once the position of the work pallet  40  has been adjusted, and the locating pins  54  are deployed, the clamping plate  47  is moved to the locked position. The clamping plate must be moved back into the receiving position before the work pallet  40  can be readjusted or removed from the work pallet receiver  44 . 
     FIG. 9 is a schematic diagram illustrating an apparatus  104 ,  106  for moving the deployable clamping plate  47  upward and downward between the “receiving” and the “locked” positions. A vertical activator  104  is connected to the deployable clamping plate  47  via a connector  106 . In a specific embodiment, the combination  104 ,  106  is provided by a cam and cam follower. In another embodiment, the combination  104 ,  106  is provided by an eccentric member and an eccentric member retainer. 
     FIG. 10 is a partial plan view illustrating an alternative configuration for the static base mount  12  and primary index axis  26 . The base  12  is essentially square and in a specific embodiment is bolted to the floor. The primary index axis is near one corner of the base  12 , providing improved support for the cantilevered members. The remaining elements are shown to provide orientation with respect to FIG&#39;S.  1 ,  2 ,  4 A and  4 B, and include the primary support member  16  (not visible), the guide support member  18 , the pair of opposed pallet guides  20 ,  22 , the secondary index axis  30 , and an upper surface  38  of the guide support member  18 . 
     We end by describing a method for using the manually operated work pallet changer and air-bearing receiver of the present invention. The method includes the following steps. 
     General Setup 
     Provide a manually operated pallet changer  10  such as that illustrated in FIG.  1 . Position the pallet changer  10  with respect to a machine tool  42 , as illustrated in FIG. 4A, so that the primary axis  26  is located to one side of the work station and so that the static base mount  12  is close to the machine tool. 
     Provide a pallet receiver  44  with an attached guide bridge  55  as illustrated in FIG. 3, and then attach the combined receiver-guide bridge  51  to the machine tool at the machine tool work station, as illustrated in FIG.  4 A. 
     Provide at least one work pallet  40 , such as the work pallet illustrated in FIG. 2, and place the work pallet on top of one of the work pallet guides  20 ,  22  as shown in FIG.  4 A. 
     Rotate the primary support member  16  and the guide support member  18  as a single unit about the primary index axis  26  away from the front of the machine tool and into a work-setup position, as illustrated in FIG.  4 B. 
     Work-piece Setup 
     Assemble work pieces on top of the work pallet  40  in an order required by the automatic machining process to be used. If a second work pallet  56  is available, place the second work pallet on top of the other work pallet guide, and assemble a second set of work pieces on top of the second work pallet. Rotate the guide support member  18  about the secondary index axis  30  as needed to provide access to each work pallet during the work-piece setup. 
     Pallet Exchange 
     Now that at least one work pallet includes assembled work pieces, rotate the guide support member  18  about the secondary axis  30  so that one work pallet guide  20 ,  22  will align with the air-bearing receiver  5   1  when the primary support member  16  and the guide Support member  18  are rotated as a single unit around the primary index axis  26  toward the front side of the machine tool  42 , as illustrated in FIG.  4 A. 
     Rotate the primary support member  16  and the guide support member  18  as a single unit about the primary index axis  26  toward the front of the machine tool so that one end of the one work pallet guide  20 ,  22  is in alignment with one end of the attached guide bridge  55  of the combined receiver-guide bridge  51 . 
     Activate the air-bearing surface of the work pallet receiver by connecting a compressed gas to emit from the plurality of small openings in the surface. Cause the locating pins  54  to withdraw below the air-bearing surface, and deploy the clamping plate  47  to the receiving position. 
     Move the one assembled work pallet  40  along the work pallet guide  22  in the direction of the work pallet receiver. Move the work pallet  40  onto the attached guide bridge  55  and then onto the air-bearing surface, guiding the opening  48  along the underside of the work pallet  40  onto the deployable clamping plate  47 . 
     Allow the air-bearing to support the assembled work pallet  40  while adjusting the position of the work pallet  40  into accurate alignment with the withdrawn locating pins  54 . When the work pallet  40  is in the proper position on the receiver  44 , deploy the locating pins  54  into the compatible openings in the bottom of the work pallet  40  and disconnect the compressed gas from the plurality of small openings to deactivate the airbearing, and move the clamping plate  47  into the locked position to secure the work pallet  40  at the machine tool work station. 
     Machining 
     When all adjustments of the work pallet  40  have been completed, rotate the primary support member  16  and the guide support member  18  as a single unit about the primary index axis  26  and away from the front of the machine tool to permit the machine tool operator  58  to monitor the machining operation. 
     Pallet Exchange 
     When the machining operations are complete, put the machine tool in a safe configuration and then rotate the primary and the guide support members as a single unit toward the front side of the machine tool so that the empty work pallet guide  22  (FIG&#39;S.  4 A and  4 B) comes into alignment with the attached guide bridge  55  (FIG.  3 ). 
     Activate the air-bearing and cause the locating pins to be withdrawn below the air-bearing surface, and deploy the clamping plate  47 , unlocking the completed work pallet  40 . 
     Move the completed work pallet  40  from the receiver  44  across the attached guide bridge  55  and onto the aligned work pallet guide  22 . 
     Now rotate the primary and guide support members  16 ,  18  about the primary index axis  26  and away from the front of the machine tool into the work setup position, as illustrated in FIG.  4 B. 
     Rotate the guide support member 180° about the secondary index axis  30  so that the other work pallet guide  20  and assembled work pallet  56  are positioned for transfer to the machine tool. Now rotate the primary and guide support members  16 ,  18  as a single unit around the primary index axis  26  toward the front of the machine tool. 
     Activate the air-bearing, withdraw the locating pins  54  below the air-bearing surface, and deploy the clamping plate  47 . Move the assembled work pallet  56  across the attached guide bridge  55  onto the receiver  44 . Adjust the position of the work pallet  56 . Cause the locating pins to deploy into the openings on the underside of the work pallet  56 . Deactivate the air-bearing, and move the clamping plate  47  into the locked position. Rotate the primary and guide support members  16 ,  18  as a single unit around the primary index axis  26  away from the front of the machine tool. Begin another machining operation. 
     Work Setup 
     While the machining operation is ongoing, disassemble the previously machined work pieces from the work pallet  40  and reassemble new work pieces onto the same work pallet. 
     Continue the process with all the work has been completed. 
     While the invention has been described in relation to the embodiments shown in the accompanying Drawing figures, other embodiments, alternatives and modifications will be apparent to those skilled in the art. It is intended that the Specification be exemplary only, and that the true scope and spirit of the invention be indicated by the following Claims.