8-8
Error Type Cause
Weak upper thread tension
Uneven upper thread
tension due to foreign
substances
Weak lower thread tension
Uneven lower thread
tension
Thread thickness
Poor timing of needle and
hook
Insufficient oil in hook
Bent needle
Bad quality needle
Tip of the needle is worn or
bent
Needle touches the hook
point
Needle touches the hook
point
Incorrect installation of
needle
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
Reference
Poor stitch
tension
Needle breaks
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