JUKI LH-3500A Series - Page 57

– 55 –
TROUBLES CAUSES CORRECTIVE MEASURES
3. Loose stitch
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.
◦
Thread the bobbin case correctly.
◦
Remove rough surface using a ne
sandpaper or polish the surface using a
bu󰀩ng wheel.
◦
Replace the bobbin or the hook.
◦
Refer to
"6-5. Adjusting the inner hook
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.
4. Thread trimming
failure
①
The position of the moving knife is
not correct.
②
Bobbin thread cannot be trimmed
by dropping the thread trimmer.
◦
Refer to
"6-9. Adjusting the position of
the moving knife" p.40
.
◦
Use the feed dog with thicker teeth (2 mm).
◦
Retard the thread trimming cam timing by 5°.
5. Amount of idling is
excessively large.
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.
◦
Increase the knife pressure.
Refer to
"6-8. Adjusting the thread
presser spring" p.39
.
◦
Re-select the bobbin and the bobbin case.
◦
Increase the spring pressure.
◦
Place the sheet in position.
◦
Decrease the thread trimming speed.
6. Clamp failure
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 o󰀨 due to
the bobbin thread slack prevention
spring of the cap hook.
④
Due to di󰀨erence 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.
◦
Increase or decrease the clamp pressure.
Refer to
"6-8. Adjusting the thread
presser spring" p.39
.
◦
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.