JUKI LK-1900S Series, Instruction Manual

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9-7. Troubles and corrective measures (sewing conditions)
Trouble Cause Corrective measures Page
1. The needle thread
slips off at the start of
bar-tacking.
① Stitches are slipped at the
start.
② The needle thread remain-
ing on the needle after
thread trimming is too short.
③ The bobbin thread is too
short.
④ Needle thread tension at
1st stitch is too high.
⑤ Pitch at 1st stitch is too
small.
◦ Adjust the clearance between the nee-
dle and the shuttle to 0.05 to 0.1 mm.
◦ Set soft-start sewing at the start of
bartacking.
◦ Correct the thread tension release tim-
ing of the thread tension controller No. 2.
◦ Increase the tension of the thread
take-up spring, or decrease the ten-
sion of the thread tension controller
No. 1.
◦ Retard the tension disk closing timing.
◦
Decrease the tension of the bobbin
thread.
◦
Increase the clearance between the
needle hole guide and the counter
knife.
◦ Decrease the tension at 1st stitch.
◦
Decrease the number of rotation at
1st stitch at the sewing start. (Extent
of 600 to 1,000 sti/min)
◦ Make the pitch at 1st stitch longer.
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2. Thread often breaks or
synthetic fiber thread
splits finely.
①
The shuttle or the driver
has scratches.
②
The needle hole guide has
scratches.
③
The needle strikes the work
clamp foot.
④
Fibrous dust is in the
groove of the shuttle race.
⑤
The needle thread tension
is too high.
⑥
The tension of the thread
take-up spring is too high.
⑦
The synthetic fiber thread
melts due to heat generat-
ed on the needle.
◦
Take it out and remove the scratches
using a fine whetstone or buff.
◦
Buff or replace it.
◦
Correct the position of the work clamp
foot.
◦
Take out the shuttle and remove the
fibrous dust from the shuttle race.
◦
Reduce the needle thread tension.
◦
Reduce the tension.
◦
Use silicone oil.
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3. The needle often
breaks.
① The needle is bent.
②
The needle hits the work
clamp foot.
③
The needle is too thin for
the material.
④
The driver excessively
bends the needle.
⑤
Needle thread is stepped
on by the work clamp foot
at the start of sewing.
(Needle bend)
◦ Replace the bent needle.
◦
Correct the position of the work clamp
foot.
◦
Replace it with a thicker needle ac-
cording to the material.
◦
Correctly position the needle and the
shuttle.
◦ Widen the distance between the nee-
dle and the wiper. (23 to 25 mm)
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4. Threads are not
trimmed.
(Bobbin thread only)
① The counter knife is dull.
②
The difference in level
between the needle hole
guide and the counter knife
is not enough.
③
The moving knife has been
improperly positioned.
④
The last stitch is skipped.
⑤
Bobbin thread tension is
too low.
◦ Replace the counter knife.
◦
Increase the bend of the counter knife.
◦
Correct the position of the moving
knife.
◦
Correct the timing between the needle
and the shuttle.
◦
In crease the bobbin thread tension.
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