carriage 22 a into and out of driving engagement with the projections 48 and 50 in accordance with the displacement of the bar 126 relative to the carriage 22 a the bracket 124 is secured to one of the drive members 52 a for vertical movement therewith and this vertical movement serves to move the vacuum connector 102 into and out of engagement with the vacuum port 88 during this vertical upward movement of the vacuum connector 102 a pneumatic piston and cylinder device 138 on the vacuum duct section 122 is employed to effect horizontal displacement of a bar 140 carrying a drive member 142 which engages a roller 144 on the closure member 90 of the port 88 in order to open this port 88 each of the table sub structures 46 as shown in fig1 is provided with two of the vacuum connectors 102 so that one of these vacuum connectors can be connected to the vacuum duct 98 during movement of the table sub structure to the transfer mechanism 55 while the other port 105 is then available for connection 142 for use during the transfer of this table sub structure 46 from the first position to the intermediate position as described above the vacuum ducts 96 and 98 are connected to a vacuum pump 148 fig8 fig1 shows the mechanisms for raising and lowering the drive members 60 and 62 into and out of engagement.