When sewing, the cross-section line or bottom line phenomenon occurs, it can be checked from the operation technology. If the reason is not found, check and handle as follows:

Step 1: check the upper channel (where the surface line passes), and see if the panel crossing port is worn, and there are deep marks and burr? Is the clamp plate too tight? Is there rust and the wire pit too deep? Or is the spring spring too elastic? Is there any hole and burr in the needle hole of the pick-up rod, panel wire hook and needle clamp hook, and needle hole of needle plate? If there is burr in the place where the line passes, it can be pulled and slippery with sand cloth or assorted small file. If the wire pit is too deep or the needle plate hole is too large, replace the new part.

Step 2: check whether the needle is too low? Is there any reverse? Check whether the needle is upright? Is the needle rubbing the edge of the presser foot and the needle hole? If there is any abnormality, it shall be adjusted to the appropriate extent as specified.

Step 3: check the down line (the position where the surface line passes under the needle plate and the bottom line passes).

(1) Remove the shuttle bed and check whether the parts of the shuttle bed are installed in wrong or reversed way? Is there too much wool in the shuttle bed? If any, cleaning and installation shall be carried out in time.

(2) Check each part in the shuttle bed - swing shuttle, shuttle core sleeve (including shuttle and shuttle screw), shuttle center, shuttle bed cover and shuttle bed ring. Check whether the position of the thread is rusted or the groove is ground out? Is there any burr? If any, the sand cloth shall be used for leveling and sliding, and if serious, new parts shall be replaced.

(3) Check if the swing shuttle is severely worn? Is the big circle edge of the swing shuttle sharp, forming the sharp angle of the cutter? If it is seriously worn, replace the swing spindle.

(4) Check the thread in the shuttle center, whether it is too full and disorderly? Is the spindle center deformed (it can be rolled in a smooth place, if it goes smoothly, it means normal)? Then install the shuttle core sleeve, pull out the bottom line, and see if there is "stuck" phenomenon? If there is "stuck" phenomenon, replace the new spindle center and conduct the test. If there is still "stuck", then we should carefully judge whether it is shuttle center or shuttle center sleeve inner circle ellipse? If it is the shuttle center ellipse, replace it with a new one. If the inner circle of the shuttle core is left unused, it can be replaced with a new one. If it is new, the outer circle edge of the spindle center can be slightly smoothed evenly with sand cloth until it is suitable.

(5) Check whether the shuttle skin is fitted and matched on the shell of the shuttle core sleeve? Can the claw of the shuttle block the bottom line and keep it from sliding out? Is the shuttle screw protruding? If not, adjust or replace new shuttle or shuttle screws.

(6) Check whether the shuttle support is normal? Are there any skid bends, rust, deep marks of wear or burr? Is the swing spring screw protruding or the screw pit burr? Is the clearance between the needle and the shuttle support too small and there is collision? If the head of the shuttle support is bent, it shall be clamped flat; If there is rust, deep abrasion mark or burr, it shall be pulled and slipped with sand cloth or replaced with a new swing support spring: if the screw head protrudes, screw down the screw or replace the new screw; If the clearance is too small, adjust to the right position.

(7) Put the shuttle bed on, check whether the head and tail of the shuttle support are stuck in the middle of the head and tail of the shuttle? Is there a deviation from the highest or lowest point, causing the surface line to pass through? Then check whether the contact clearance between the shuttle and the shuttle support is too small? If there is any abnormal phenomenon mentioned above, adjust it until it is appropriate.

Step 4: after the above inspection and adjustment, there should be no broken line phenomenon, and the joint can be tested. If there is still a broken line, it is necessary to recheck. Or wear the surface and bottom line, press the sewing material, and use your hand to move the upper wheel, and slowly try to sew. There is a stuck cutting phenomenon on the bottom line of the surface, and then "the medicine is applied to the right problem" to eliminate the fault.

The problems at this time are generally the following:

(1) If a new cloth feeding tooth is replaced, should the cloth feeding tooth face be checked to see if it is too sharp? Is the pressure on the foot too high? If the tooth surface is too sharp, use sand cloth to carefully pull the tooth surface slightly. If the pressure of the presser foot is too large, adjust the pressure of the foot.

(2) Check the angle of the feeding cam to see if the cloth feeding is too fast? Adjust to the appropriate condition.

(3) Is the surface line stuck by shuttle door? If shuttle door is too old, it can be replaced with shuttle spring and shuttle door.

(4) If there is burr in the needle groove and needle eye, it can be replaced with a new machine with good quality for needle test sewing. Or pull the suture back and forth several times through the needle eye. If the hair is still rising, change the needle. By this time, if it is a new machine, there should be no broken thread phenomenon, only those very old sewing machines will have this phenomenon. When the upper wheel is slowly sewn by hand, if the thread ring of the surface is not turned to the center line of the shuttle bed, the thread pick-up bar starts to lift the line. This is a phenomenon that the swing angle of the swing shuttle is too small, which can reduce the distance between the center point of the lower shaft hole of the lower axle crank and the center point of the cycloid slider. But this technology is more complex, it is better to send it to the repair department for adjustment and repair.