Abstract
A motion diagram showing the relative motion of various machine parts is necessary in order to fully understand, whether the machine properly fulfills its functions. However, in the case of a sewing machine, conventional motion diagrams for both the machine and sewing thread are usually used. This suggests that only a part of the sewing thread motions is given in connection with the machine motion.
In this paper, new sewing thread motion diagrams involving various sewing factors such as fabric thickness, stitch length, and thread elongation are proposed for a lockstitch sewing machine. By using the new motion diagrams, it is shown that the relation between needle thread movement and tension changes during one cycle of sewing. It is also shown how the various sewing factors affect the tightening of stitches in the process of stitch formation.
