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12. CAUSES AND CORRECTIVE MEASURES FOR PHENOMENA IN
SEWING
Phenomenon Cause Corrective measures
1. Thread break-
age
(Thread frays or
is worn out.)
①
Thread path, needle point, hook blade
point or bobbin case resting groove
on the throat plate has sharp edges or
burrs.
◦
Remove the sharp edges or burrs on the blade
bobbin case resting groove on the throat plate.
②
Needle thread tension is too high.
◦
Decrease the needle thread tension.
③
Bobbin case opening lever provides
an excessive clearance at the bobbin
case.
◦
Decrease the clearance provided between the
bobbin case opening lever and the bobbin.
Refer to
"8-4. Adjusting the bobbin case
opening lever" p.110.
④
Needle comes in contact with the
blade point of hook.
◦
Refer to
"8-1. Needle-to-hook relation" p.105
.
⑤
Amount of oil in the hook is too small.
◦
Adjust the amount of oil in the hook properly.
Refer to
"4-9-1. Adjusting the amount of oil in
the hook" p.35
.
(Needle thread
trails 2 to 3 cm
from the wrong
side of the fab-
ric.)
⑥
Needle thread tension is too low.
◦
Increase the needle thread tension.
Refer to
"8-1. Needle-to-hook relation" p.105.
⑦
Thread take-up spring works exces-
sively or the stroke of the spring is too
small.
◦
Decrease the tension of the spring and increase
the stroke of the spring.
⑧
Timing between the needle and the
hook is excessively advanced or re-
tarded.
◦
Refer to
"8-1. Needle-to-hook relation" p.105
.
⑨
Thread untwines.
◦
Wind the thread on the needle.
⑩
Uniform thread loops cannot be
◦
Use the thread guide equipped with felt pad.
◦
Use the optional needle clamp wire.
(Bobbin thread
comes out of
the bobbin.)
⑪
Bobbin is wound with excessive
-
ment thread)
◦
Wind the bobbin with thread by 80 % of its
capacity.
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