1. The presser foot groove is seriously skewed, the presser foot fastening screw is not tightened, the needle plate hole and the needle are concentric, and the lower shaft axial clearance is too large; the position and clearance of each component are properly adjusted. For machines with poor concentricity between the needle and the needle plate, adjust the position of the needle plate or after the needle is raised to the highest position, tap the lower end of the needle bar to correct the center position.

2. Since the plane of the tip of the hook is lower than the plane of the needle groove of the shuttle; the plane of the needle groove is lower than the plane of the tip of the hook by 0.15mm or level, so that the needle groove of the shuttle can neither touch the needle nor Plays a role in needle protection.

3. The gap, spacing, and height of the hook and the needle are not correct; according to the standard, reasonable adjustment.

4. When the feeding teeth and the needle bar are in the wrong position, the feeding teeth are still feeding, which causes the needle to break; the position of the eccentric can be adjusted according to the requirements, and the needle is separated from the sewing material. At 3 mm, the feed dog should be fed.