Abstract: Two workpiece portions (30, 32) that are to be stitched together along a stitching path (28) each have a stitching region (24, 26) which corresponds to the stitching path (28), but which is so shaped that the regions do not overlap when the workpieces (30, 32) are in a substantially flat condition. Thus some three-dimensional shaping is imparted to the portions during stitching. Each of the workpiece portions (30, 32) is clamped between two rollers (10, 12, 24) one of which is driven and the other freely rotatable, the driven rollers (10, 12) serving to distort the stitching regions into a desired overlapping position progressively in preparation for each successive stitching operation. The rollers are also bodily movable to advance the workpiece portions (30, 32) step-by-step through the operating locality (4) of the sewing machine. For sensing when the stitching regions are in the desired overlapping relationship suitable edge sensing means (40, 42, 44) is provided.