Method of and apparatus for the production of button-holes on a double lock stitch buttonhole sewing machine

摘要

So-called raised buttonholes are sewn on a double-lock-stitch sewing machine with the fabric workpiece turned face down on the stitchplate of the sewing machine and the upper-thread tension being such that the interlocking loops of the upper and lower threads lie upon the downwardly facing side of the workpiece. According to the invention, the upper-thread tension at the end of a buttonhole-stitching cycle for the fastening stitch is increased above the lower-thread tension temporarily so that the interlocking loops of the upper and lower threads during this last fastening stitch lie within the thickness of the material or on the upper face of the downwardly turned workpiece.