means of the guide to be displaced without any impediment or obstruction the sewing machine is now started and an electric pulse reaches the first electrovalve 44 causing it to open and thus acting on the pilot mechanism of the distributor box 40 as a result switching occurs from the conduit 39 to the conduit 41 which produces the lowering of the rod 26 of the gripping means on the underlying pieces of fabric such that the latter are held against the lower plate 22 of the guide 13 the guide is therefore drawn towards the sewing machine 2 and during this movement it keeps the pieces of fabric aligned according to the sewing axis 6 more specifically stitching is also executed parallel to the profile of the edge in the part occupied by the pockets owing to the fact that an auxiliary guide 13a is provided in a fixed position adjacent the presser foot 4 this auxiliary and conventional type guide is effective in moving the aforementioned portions of the fabric at right angles to the sewing axis 6 by means of its respective vertical wall 13b thus although the pieces 100 have a curvilinear edge in the portions occupied by the pockets as shown in fig4 the wall 13b is.