How to repair the flat sewing machine that cannot automatically cut the thread

The inability of a sewing machine to automatically cut threads is usually caused by loose mechanical connections, inaccurate thread cutting timing, or electrical control system failures. It is necessary to sequentially inspect the mechanical components, adjust the cam position, and check the circuit.
Mechanical component inspection and cleaning
Check the tool holder connecting rod: Confirm whether the screw of the tool holder connecting rod is loose. If it is loose, tighten and fix it. This is a common reason for not cutting the wire despite the action. ‌‌
Cleaning foreign objects and blades: Open the needle plate to clean the thread debris, check whether the moving and fixed blades are worn, and replace or grind the blades if they become dull. ‌‌
Adjust the bite gap: Ensure that the bite amount between the moving blade and the fixed blade is between 1.5-2.0mm, and the fixed blade should exceed the circular hole of the moving blade cable by about 2mm
Cutting line timing and position calibration
Calibrate the parking space: After the machine stops, the height from the needle tip to the needle plate should be 11-12mm. If it is not correct, adjust the parking space again. ‌‌
Adjust cam timing: Loosen the thread cutting cam screw and align the highest point of the cam with the roller. If the thread cutting is too early or too late, delay or advance the cam fitting time. ‌‌
Check the retraction amount of the cutting blade: Adjust the left and right positions of the wire cutting cam to achieve a retraction amount of 3-5mm for the cutting blade. ‌
Electrical control system and parameter reset
Test the electromagnet: Step on the pedal and listen for the "ticking" sound of the electromagnet. If there is no sound, check the circuit connection or replace the electromagnet. ‌‌
Factory reset: If the mechanical adjustment is ineffective and the machine operation is out of control, it may be due to a disorder in the control box program, which can be resolved by restoring the factory settings. ‌
Adjust thread tension: When cutting the thread is difficult, reduce the tension of the first gripper appropriately to avoid the thread end being too short and falling out of the needle hole. ‌‌