JUKI SC-956, Instruction Manual

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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
point of hook using a fine emery paper. Buff up the
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
formed when making chain-off thread.
◦ 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
amount of thread. (In particular, fila -
ment thread)
◦ Wind the bobbin with thread by 80 % of its
capacity.