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Phenomenon
Cause Corrective measures Page
Loose
stitch
When the needle thread tension is too low.
When the tension of the thread take-up
spring is too low.
When the tension of the bobbin thread is
too high.
When the timing of the sewing hook and
the needle is not matched.
When the thread is too thick for the needle.
When the thread slips out of the rotary
disc.
○
Increase the needle thread tension.
○
Increase the tension of the spring.
○
Decrease the bobbin thread tension.
○
Adjust the timing correctly.
○
Use a suitable needle or thread.
○
Increase the tension of the preten-
sion disk.
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29
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24
Irregular
stitch tight-
ness
When the bobbin thread tension is too
low.
When the bobbin thread is not wound
correctly.
When there is a scratch on the thread
path of the sewing hook, bobbin case,
thread take-up lever or any other parts.
○
Increase the bobbin thread ten-
sion.
○
Wind up the bobbin thread even-
ly.
○
Remove such a scratch or replace
the component.
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22
Needle
breakage
When the needle is bent.
When the quality of the needle is not
good.
When the needle is not entirely inserted
into the needle bar.
When the needle hits the sewing hook.
The needle is too thin for the sewing
material and thread.
The needle hole in the throat plate is too
narrow.
The needle hits against the throat plate.
The needle hits against the presser
foot.
○
Replace it with a new needle.
○
Use a needle of good quality.
○
Insert the needle into the needle
bar as far as it will go.
○
Adjust the timing and clearance
between the needle and the sew-
ing hook and also the position of
the needle guard.
○
Replace a suitable needle.
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126
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