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When the hook timing is slow
When the hook timing is fact
8.6.5) Relations Between Thread Take-up Lever and Hook
The setting of hook point timing in accordance with the needle movement has a great impact on thread
tightness and thread break. The figures below show the location of the hook when the thread take-up lever
ascends from the lowest point (the rotary angle of the main shaft: 291°).
This is the case where the hook's groove is located
within (A). If the loop created by the thread is too
small, the hook point moves inside to hook the upper
thread. Then, the stitch will be created much quicker
compared with the ascending movement of the thread
take-up lever. Therefore, as a result, the thread
tightening becomes poor, and the upper loop becomes
too small, causing thread skip.
This is the case where the hook's groove is located
within (B). The hook point will hook the thread when
the loop is too big. In this case, thread skip might not
occur, but thread break could occur since the time
taken for the thread to escape from the hook is shorter
than the thread take-up lever's ascending movement.
Too Small
Too Big
(B)
(C)
(A)
If the hook timing is normal, the hook's groove will be located within (C).
CAUTION