Influence of Fabric External Friction Force and Certain Parameters of a Sewing Machine Upon Stitch Length

In the process of stitch formation sewing garment is affected by various friction forces. Magnitude of these forces decides the slip of sewing garment with respect to a tooth plate and move from inertia later on. In this case the sewing garment is affected by external friction force, which depends not only on the properties of sewing garment, but on the magnitude of pressing force, type of pressing foot and on the sewing speed as well. The article discusses the influence of pressing foot design, pressing force and sewing speed upon the stitch length. Experiment were performed using the universal pressing foot with even metal base, the pressing foot with teflon base and the pressing foot to which two rotation plastic rings are attached. The paper analyses three fabrics with different setting, thickness and raw materials. For experiments “Gütermann ” sewing threads No. 120, 100 % of PES were used. Rotation speed of the main shaft of the sewing machine was selected 600, 1600 and 2600 min–1. The special device for the determination of the external friction force was created. There was determinated that the highest (80 N) external friction force was received performing experiments with the pressing foot having even metal base and lowest friction force (20 N) was determinated with the pressing foot having rotation rings. Dependences of stitch length shows that different friction forces cause the variation of the stitch length in range of 10 – 20 %. The tendency of variation of the stitch length is more clear when the sewing speed is highest