Detailed explanation of the causes and maintenance methods of bubble formation in the sewing thread

How to repair bubbles in the stitching of the new sewing machine?
First, check if the stitching is too loose, and then inspect the parts of the machine head to see if any parts are loose.
How to maintain the new sewing machine?
Regularly wipe and clean, apply engine oil frequently when using, and apply oil to areas with holes. It's best to wipe it once a week, as large factories usually wipe it once a week. If not necessary, it is necessary to solve the oil problem.
How to repair the new sewing machine's jumper and bubble thread?
Check if the thread picking spring is tight and if the sleeve needle is on the needle back and forth. If the iron sheet of the needle blocking plate passes through the sleeve needle too low, it will hang a section of wire and cause bubbles. Jump the wire and check if there is any skewness before the large and small bearings inside, or if the blade is worn too much. It is the small iron fast connected to the triangle of the hook wire.