ABSTRACT
The motion of sewing thread between the bobbin and the stitch is a complex and highly dynamic process, repeated more than 100 times per second. Chapter 4 provides a step-by-step analysis of the required length of needle (or upper) thread, which is needed for the stitch formation process to work properly. This process is analyzed for all phases of lock stitch building, where friction between the thread and the needle is high, because the thread has to pass, in some situations, up to 80 times through the needle eye until it is placed in the seam. After considering the lock stitch, the differences in the thread motion during chain stitch building are discussed. Chapters 3 and 4 provide the background to understanding sewing machine processes.
