When using synthetic sewing thread, the tension of sewing thread must be carefully determined and adjusted to the minimum. The tension of the bottom thread must be adjusted so that when the free end of the suture is pulled up, the sheaths of the bobbin and the bottom thread slowly slide down, and the tension of the upper thread and the bottom thread must be the same, so that they are just interwoven between the two layers of cloth. When the tension of synthetic sewing thread is too large, it will automatically shrink to relieve this tension, so that the garment body will shrink along the seam and wrinkle the seam.

The shortening of the lower fabric as mentioned above is due to the friction between the upper fabric and the presser foot, which forces the lower fabric on the feed teeth to move faster, resulting in wrinkles at the seams. The pressure of presser foot can be reduced as much as possible, and at the same time, the rotating speed of sewing machine can be reduced by fine tooth cloth feeder (conveyor), so that the wrinkling caused by feeding can be avoided, and the best way to solve this problem is to adopt sewing machine with differential feeding or needle feeding mechanism.