Tune up the thread tension.
First check whether the wrong thread, the bobbin case has been stuck, if these are not a problem, it is the top thread loose or bottom thread tight, micro-tuning on the line.
If you are sure that the lead is correct, the reason is that the thread clamp has lost its function, or maybe there is thread hair between the two round pieces of the thread clamp affecting the tightness, or maybe the thread clamp has lost tension on the Pagoda spring, you check to see.
Extended information:
Machine Maintenance
Cleaning Methods
1, the cleaning of the cloth feeding teeth: remove the screw between the needle plate and the cloth feeding teeth, remove the cloth hairs, dust, and add a small amount of sewing machine oil.
2, the cleaning of the shuttle bed: the shuttle bed is the core of the work of the sewing machine, but also the most prone to failure, so it is necessary to often remove dirt and add a small amount of sewing machine oil.
3, other parts of the cleanup: the surface of the sewing machine and the various parts of the panel should be frequently cleaned to keep clean.
Sewing machine oiling and lubrication methods:
1, oiling parts: the head of the oil holes, lubrication of the upper shaft and the upper shaft of the connected parts; the panel of the parts and the parts connected to the movable parts; lubrication of the presser foot lever and the needle bar and the parts connected to it; the machine board of the lower part of the parts of the movable parts of the wiped clean and add a small amount of oil.
2, maintenance of sewing machines should pay attention to: after the work is completed, the needle will be inserted into the needle hole plate, lift the presser foot, but also with the machine cover cover the machine head, in order to prevent the intrusion of dust and chips; start to work, check the main parts, step up the weight of the situation, whether there is a special sound, whether the needle is normal, and so on, such as the discovery of abnormalities, it should be promptly overhauled; the machine is used for quite a long time after a major repair. Overhaul, such as the discovery of wear and tear of the parts, to replace the new.
Reference:
(Baidu Encyclopedia: Sewing Machines)