box assembly generally designated 20 and a lower male die box assembly generally designated 22 the thermoplastic sheet or web s is incrementally indexed between the upper and lower mold assemblies 20 and 22 in the usual manner by pairs of superimposed nesting upper and lower endless chains 24 which are described more particularly in u s pat no 3 217 852 incorporated herein by reference the female die box assembly includes a plurality of spaced apart mold cavities 28 the upper die box assembly 20 includes a vacuum manifold chamber 29 which connects to the cavities 28 by means of passages 31 and a line member 33 is employed to connect the vacuum manifold chamber 29 with a conventional rotary pump and surge tank the general construction of the upper and lower die box assemblies 20 and 22 is more particularly illustrated in u s pat no 3 346 923 which is incorporated herein by reference the upper female die box assembly 20 is mounted on an upper moveable platen generally designated 32 having a pair of guides 34 which furnish guide surfaces for vertical travel of the upper platen 32 on vertical slides 36 fixed to the side rails 18 platen moving apparatus generally designated 38 is provided for moving the upper platen 32 and includes a drive shaft generally designated 40 journalled on a pair of spaced apart bearing blocks 42 depending from the frame header 16 a pair of relatively short toggle links 44 are fixed to the drive shaft 40 and is coupled to a pair of relatively long toggle links 46 via pivot pins 48 the lower ends 50 of the longer pair of toggle links are pivotally coupled to toggle blocks 52 which are fixed to the upper side of.