JUKI LH-4500C Series Instruction Manual page 185

Phenomenon
① The position of the moving knife is not
4. Thread trim-
correct.
ming failure
② Bobbin thread cannot be trimmed by
dropping the thread trimmer.
① The counter knife pressure is
5. Amount of idling
inadequate.
is excessively
large.
② Backlash between the bobbin and the
bobbin case is excessively large.
③ The idling prevention spring does not
work adequately.
④ The idling prevention sheet is not
placed.
⑤ Thread trimming speed is too high.
① The clamp pressure has adjusted to an
6. Clamp failure
excessively high or low value.
② The clamp pressure works excessively,
resulting permanent set in fatigue of
the clamp plate clamp spring.
③ The bobbin thread slips off due to the
bobbin thread slack prevention spring
of the cap hook.
④ Due to difference in thread count
number between the needle thread and
bobbin thread, they excessively tangle
with each other at the time of thread
trimming.
⑤ The feed dog height is too low.
① Needle thread tension is inadequate
7. Isolated idling
loops during when sewing at a low speed.
intermittent
sewing with
thick thread
(Core spun yarn
#8)
② Amount of movement of the thread
take-up spring is inadequate.
③ Thick thread at the let needle fails to
come off the hook smoothly.
Cause
◦ Refer to
◦ Use the feed dog with thicker teeth (2 mm).
◦ Retard the thread trimming cam timing by 5°.
◦ Increase the knife pressure.
◦ Re-select the bobbin and the bobbin case.
◦ Increase the spring pressure.
◦ Place the sheet in position.
◦ Decrease the thread trimming speed.
◦ Increase or decrease the clamp pressure.
◦ Change the clamp plate clamp spring with a new
◦ Remove the bobbin thread slack prevention
◦ Use the optional clamp style cap hook.
◦ Increase the tension applied by the tension
◦ Retard the timing of the thread trimming cam.
◦ Increase the feed dog height.
◦ Increase the AT correction value for the left needle
◦ Increase the amount of movement of the thread
◦ Adjust the timing at which the left-thread is
– 180 –
Corrective measures
"8-5. Adjusting the position of counter
knife, knife pressure and clamp pressure 8-5.
Adjusting the position of counter knife, knife
pressure and clamp pressure" p.111
Refer to "8-5. Adjusting the position of counter
knife, knife pressure and clamp pressure 8-5.
Adjusting the position of counter knife, knife
pressure and clamp pressure" p.111
Refer to "8-5. Adjusting the position of counter
knife, knife pressure and clamp pressure 8-5.
Adjusting the position of counter knife, knife
pressure and clamp pressure" p.111
one.
spring.
controller No. 1.
at a low speed (200 - 1,000 sti/min) by 150 % or
more.
"6-3. Tension correction (with respect
Refer to
to sewing speed)" p.95.
take-up spring.
scooped by the left hook to the point that is 16 mm
± 0.15 mm above the lower point of needle bar.