1, the needle is not installed in place, the installation direction is wrong, or the model is wrong.
2. The spool is not installed properly. If the cable is wound in the spool sleeve, the tension spring of the cutter action hook of the flat seam buttonhole sewing machine is easy to fatigue due to long-term use, which will cause insufficient tension, so attention should be paid to adjustment or replacement.
3. Loose transmission mechanism leads to unsynchronized needle and shuttle, and the hook of cutter action is bad. It is necessary to effectively adjust the buttonhole of the flat buttonhole sewing machine according to the standard.