The first step is to check the upper thread path (the place where the upper thread passes), and see whether the thread passing port on the panel is worn, deep marks or burrs? Is the clamping plate clamped too tightly? Is there any rust or deep hole? Or is the thread take-up spring too strong? Are there any pits and burrs in the thread take-up hole, the panel thread hook and the needle clamp thread hook, and the needle hole in the needle plate? If there are burrs in the place where the thread crosses, use emery cloth or assorted small files to slide it. If the thread hole is too deep or the needle plate hole is too large, replace with new parts.
The second step is to check whether the needle is installed too low? Is it reversed? Check whether the needle is upright? Does the needle rub the presser foot and the edge of the needle hole? If it is abnormal, it should be adjusted until it is suitable according to regulations.
The third step is to check the lower thread path (the part where the upper thread passes under the needle plate and the bottom thread passes).
(1) Disassemble the shuttle bed and check-are there any wrong or reverse installation of the shuttle bed parts? Is there too much lint in the shuttle bed? If so, they should be cleaned and installed in time.
(2) Check every part in the shuttle bed-the shuttle, the bobbin case (including the bobbin and the bobbin screw), the bobbin, the bobbin cover, the bobbin ring, and see if the thread position is rusty or Grind out pits? Are there any glitches? If there is, use the sand blading for smoothing and slipping. In serious cases, replace with new parts.
(3) Check whether the shuttle is severely worn? Is the big round edge of the shuttle sharp, forming an acute angle for cutting hands? If it is severely worn, replace the shuttle with a new one.
(4) Check whether the thread in the bobbin is too full and messy? Is the bobbin deformed (you can roll the bobbin in a smooth place, if it walks smoothly, it is normal)? Then install the bobbin case and pull out the bottom thread to see if there is a "stuck" phenomenon? If there is a "stuck" phenomenon, a new bobbin should be replaced and the test should be performed again. If there is still "stuck", you need to make a careful judgment to see if it is the bobbin or the inner circle ellipse of the bobbin sleeve? If it is an oval bobbin, it should be replaced with a new one. The inner circle of the bobbin case is elliptical. If it is worn out, you can replace it with a new one. If it is new, you can use emery cloth to slightly grind the outer circle of the bobbin until it fits.
