A Study of Thread Tensions on a Lockstitch Sewing Machine (Part I)

A study of thread tensions on a lockstitch sewing machine was made, measuring simultaneously both the needle and bobbin thread tensions. Experiments were carried out under specified sewing conditions, whereby needle and bobbin thread tensioner adjustment, sewing speed, number of plies, fabric quality and sewing thread quality were varied in order to investigate the effect of these factors on the needle and bobbin thread tensions. The patterns of the thread tension traces obtained were analysed as well as the effect of these factors on the peak tensions detected on both thread tension traces. Four significant peak tensions on the needle thread tension trace and two significant peak tensions on the bobbin thread tension trace were detected, during a stitch cycle. It was found that no significant variations occurred as far as the timing and shape of the peak tensions were concerned. However, variations were detected in the peak tensions according to the sewing conditions, as expected. From the analysis of the data obtained, multiple regression equations were derived to predict, with a good degree of accuracy, the peak tensions generated, according to the sewing conditions.