of which is hinged on the free end of an arm 12 secured at the other end to a pin 13 the pneumatic cylinder comprises supply conduits 14 and 15 rigidly connected to the pin 13 is a plate 16 which is movable between the operative position indicated by the dotted line in the figure and an inoperative position in which it is disposed on top of the means 17 designed to raise the movable plate with respect to the position which it normally takes up when it is in the operative position it should be noted that plate 16 covers or crosses the sewing axis when it is in its operative position separating layers of fabric and that it does not cross the sewing axis when it is in its inoperative position a plurality of plates similar to plate 16 can be used if desired to form a plurality of fabric guide channels and the vertical position of these plates can be achieved by means of the adjusting mechanisms described below it should be noted that plate 16 covers or crosses the sewing axis when it is in its operative position separting layers of fabric and that it does not cross the sewing axis when it is in its inoperative position the means 17 consists essentially of a projection in the form of a hemispherical cap secured to the work surface 2.