The specific inspection method is: while pressing the cam follower (group) in the B direction, slowly reverse the handwheel. When the cam driving roller of the cam follower enters the cam groove R of the tangent cam, the handwheel just feels blocked. At this time, make sure that the engraved dots on the nose are aligned with the red engraved dots on the handwheel.
If the matching time is too early, the suture will easily come out of the needle (short after the upper thread is cut), and it may also cause poor thread trimming of the upper and lower threads, and poor thread take-up during thread trimming. If the matching time is too late, it is easy to cause the needle and the thread remover to collide and cause poor thread cutting.
There are several reasons why the sewing machine cannot hook the bottom thread:
1. The time and gap between the straight needle and the tip of the hook or the tip of the rotary hook are wrong. The correct thing is that when the straight needle drops to the bottom point and starts to move up 3--4mm, the tip of the hook is at the center of 1.5mm above the needle hole of the straight needle. At this time, the gap between the straight needle and the tip of the hook is 0.5mm.
2. There is foreign matter in the rotary hook frame. During the use of the sewing machine, thread ends will be wound on the center rod of the rotary hook frame or there will be too much dust in the rotary hook frame. When there is too much thread or dust in the rotary hook, we will cause the lock cylinder to be stuck after installing the lock case. At this time, the lock cylinder cannot rotate and the bottom thread cannot be brought up.
3. The position of the needle bar moves up. When the sewing machine is in use, the fastening of the straight needle connecting column is slightly loosened, which will cause the needle bar to move up, and the tip of the hook will pass under the needle eye, causing the bottom thread to fail to hook up.
4. The sewing machine needle is bent. After the sewing machine needle has been used for a long time (especially the small needle), the gap between the needle and the tip of the rotary hook is too large after the needle has been used for a long time, and the bottom thread cannot be hooked up. But in this case, the jumper will happen first.
