Before the silk fabric is unsanded, the fabric is very sturdy and hard in the sewing process. As a result, the needle and the suture cannot produce a good loop in the sewing material, and a jump stitch is formed. Check the needle bar for wear and clearance, check that the hook tip is good and standard, because the hook tip is a key component of the hook line. Do not have burrs, baldness and other problems, as found. It should be repaired in time with diamonds or oil stone metallographic sandpaper. Then, adjust the angle of the needle bar and check the height of the needle bar. The height of the needle bar is: when the needle bar is at the bottom dead center, the needle bar scale should be on the second line. Thus, when the needle bar is raised to the first line, the angle between the needle and the hook tip is adjusted to be optimal. First adjust the angle: If the needle bar has a slight gap, push the needle bar to the left with your left hand and adjust it. The angle standard for adjusting the needle and the hook is: when the needle bar rises from the bottom dead center to the off-site mark, the hook tip should be 1.1-1.5cm on the needle, and the hook tip and the needle-to-book gap are 0.2cm. -0.05cm, the feeding mechanism is also the key. First check whether the feeding cam is standard. Because the thin material is sewn, the teeth should be lower, and the feeding cam should be properly adjusted.