JUKI LH-3500A Series Instruction Manual page 57

TROUBLES
3. Loose stitch
4. Thread trimming
failure
5. Amount of idling is
excessively large.
6. Clamp failure
CAUSES
① Bobbin thread does not pass
through the forked end of the
tension spring on the bobbin case.
② Thread path has rough surface.
③ Bobbin does not spin smoothly.
④ Bobbin case opening lever
provides too much clearance at
the bobbin.
⑤ Bobbin thread tension is too low.
⑥ Bobbin is wound too tightly.
⑦ The presser foot does not securely
press the multi-layered section of
the material.
⑧ Needle eyelet is too small for
thickness of thread, preventing
smooth take-up motion of the
thread take-up lever.
⑨ With respect to tensing of thick
thread, neither needle thread
tension nor bobbin thread tension
can be increased, resulting in
production of isolated idling loops.
⑩ Isolated idling loops are produced
during the reverse feed stitching.
① The position of the moving knife is
not correct.
② Bobbin thread cannot be trimmed
by dropping the thread trimmer.
① The counter knife pressure is
inadequate.
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 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.
CORRECTIVE MEASURES
◦ Thread the bobbin case correctly.
◦ Remove rough surface using a fine
sandpaper or polish the surface using a
buffing wheel.
◦ Replace the bobbin or the hook.
◦ Refer to
guide" p.37.
◦ Adjust the bobbin thread tension.
◦ Adjust the tension components on the
bobbin winder.
◦ Change presser foot with the hinging
presser (B1524512FBE).
(The presser foot with large front and rear
elevation angles is preferable.)
◦ Retard the hook timing by 2 to 3 degrees.
◦ Use the needle thread take-up eyelet.
◦ Use the needle thread presser.
◦ Use the bobbin thread tension spring t0.3
(22612808).
◦ Retard the hook timing.
◦ Refer to
the moving knife"
◦ Use the feed dog with thicker teeth (2 mm).
◦ Retard the thread trimming cam timing by 5°.
◦ Increase the knife pressure.
Refer to
presser spring"
◦ 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.
Refer to
presser spring"
◦ Change the clamp plate clamp spring with a
new one.
◦ Remove the bobbin thread slack prevention
spring.
◦ Use the optional clamp style cap hook.
◦ Increase the tension applied by the tension
controller No. 1.
◦ Retard the timing of the thread trimming
cam.
◦ Increase the feed dog height.
– 55 –
"6-5. Adjusting the inner hook
"6-9. Adjusting the position of
p.40.
"6-8. Adjusting the thread
p.39.
"6-8. Adjusting the thread
p.39.