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No
Symptom
Upper thread
4
does not sink.
Lower thread
5
does not sink.
6
Trimming errors
Upper thread is
pulled out when
7
sewing
commences.
Checkpoints
Tension of fixed blade
Edge of movable and fixed
blades
Direction of needle
Check the crossing of
trimmer cam notch mark
and blade
Check the Up-stop position
of needle
Root cause
Too tight upper thread tension.
Too loose lower thread tension.
Too weak upper thread tension.
Too strong lower thread tension.
Tension not aligned between
movable and fixed blades.
Abrasion in blade groove of
movable and fixed blades.
Wrong needle insertion.
Insufficient crossing quantity of
movable and fixed blade.
Too strong upper thread tension.
Too thick a needle for thread.
Take-up lever pulls out the upper
thread because the needle up
and down position is too high.
Corrective action
Reduce tension of upper thread.
Increase tension of lower thread.
Increase upper thread tension.
Decrease tension of lower thread.
Adjust tension of movable and
fixed blade.
Replace movable and fixed
blades.
Reinsert the needle correctly.
Adjust the strokes of movable
and fixed blades.
Adjust tension of upper thread.
Check thickness of needle.
Adjust the up-stop position of
needle.
47
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