12-8
Error Type
Cause
①
Weak upper thread tension
②
Uneven upper thread
tension due to foreign
substances
③
Weak lower thread tension
④
Uneven lower thread
tension
⑤
Thread thickness
⑥
Poor timing of needle and
hook
⑦
Insufficient oil in hook
①
Bent needle
②
Bad quality needle
③
Tip of the needle is worn or
bent
④
Needle touches the hook
point
⑤
Needle touches the hook
point
⑥
Incorrect installation of
needle
⑦
Needle touches the needle
hole on the plate
Inspection & Repair
Adjust tension
Clean main and sub tension
adjusters in the thread tension
adjusting plate
Adjust tension
Clean bobbin case and check
tension on bobbin spring
Change to quality thread
Adjust timing
Oil the raceway of hook
Change needle
Space the needle and the hook
point
Correct the installation
�
Check if needle plate is
unscrewed
�
Adjust the position of the
needle bar
Ref. 5-10, 5-6) 2)
Ref. 5-12, 5-7) 2)
Ref. 5-19, 5-12)
Ref. 10-3, 10-3) 1)
Ref. 5-19, 5-12) 3)
Ref. 5-21, 5-12) 4)
Ref. 5-19, 5-12) 3)
Ref. 11-7, 11-6)
Reference
Poor stitch
tension
Needle breaks