Troubles And Corrective Measures (Sewing Conditions) - JUKI LK-1900BN Series Instruction Manual

9-7. Troubles and corrective measures (sewing conditions)

Trouble
1. T h e n e e d l e t h r e a d
slips off at the start of
bar-tacking.
2. Thread often breaks or
synthetic fiber thread
splits finely.
3. T h e n e e d l e o f t e n
breaks.
4. T h r e a d s a r e n o t
trimmed.
(Bobbin thread only)
Cause
① Stitches are slipped at the
start.
② The needle thread remain-
i n g o n t h e n e e d l e a f t e r
thread trimming is too short.
③ The bobbin thread is too
short.
④ Needle thread tension at
1st stitch is too high.
⑤ Thread clamp is unstable
(material is apt to be ex-
panded, thread is hard to
slide, thread is thick, etc.).
⑥ Pitch at 1st stitch is too
small.
① The shuttle or the driver
has scratches.
② The needle hole guide has
scratches.
③ The needle strikes the work
clamp foot.
④ F i b r o u s d u s t i s i n t h e
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.
① The needle is bent.
② The needle hits the work
clamp foot.
③ The needle is too thin for
the material.
④ T h e d r i v e r e x c e s s i v e l y
bends the needle.
⑤ Needle thread is stepped
on by the work clamp foot
a t t h e s t a r t o f s e w i n g .
(Needle bend)
① The counter knife is dull.
② T h e d i ff e r e n c e i n l e v e l
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.
－
Corrective measures
◦ 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.
◦ 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)
◦ Increase the number of stitches of
thread clamp to 3 to 4 stitches.
◦ Make the pitch at 1st stitch longer.
◦ Decrease the needle thread tension
at 1st stitch.
◦ 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.
◦ 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)
◦ 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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