viewed in fig1 so as to define a space between the rail of the tuck clamp and the vacuum chamber the plenum for the vacuum chamber is connected with a conventional conduit to a selectively operable vacuum pump 132 positioned within the housing the tucker blade 98 is a horizontal elongated blade of thin profile extending the full width of the apparatus 41 and mounted on a horizontal support plate 133 secured to the rack 134 of a rack and pinion reciprocal drive system 136 fig1 the pinion 138 of the drive system is reversibly driven by a motor not seen obviously rotation of the pinion in one direction drives the rack and the tucker blade horizontally to the right as viewed in fig1 into an extended position as seen in fig1 while rotation of the pinion in the opposite direction retracts the tucker blade to its retracted position of fig1 in the extended position shown in fig1 it is extended between the upper clamp jaw 108 and platen 112 of the tuck clamp 100 with the front elongated edge 140 of the tucker blade being positioned beyond the tuck clamp immediately adjacent to the sewing carriage 82 the horizontal support plate 132 on which the tucker blade is mounted is supported on a lever arm 142 pivotal about a pivot shaft 144 by a pair of low pressure pneumatic cylinders 145 which could in fact be a gas spring even though in the disclosed embodiment it is a pneumatic cylinder carrying low pressure the pneumatic cylinders are therefore adapted to pivot the lever arm and thus the tucker blade about the pivot shaft for a purpose to become clear hereafter a lower clamp 146 is positioned beneath the tucker blade.