Troubles And Corrective Measures (Sewing Conditions) - JUKI AB-1351 Instruction Manual

1-17. Troubles and corrective measures (sewing conditions)

Trouble
1. The needle 1 Stitches are slipped at the start.
thread slips
off at the
start of bar-
tacking. 2 The needle thread remaining 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 Thread clamp is unstable (material is
apt to be expanded, thread is hard to
slide, thread is thick, etc.).
6 Thread clamp is unstable (material is
apt to be expanded, thread is hard to
slide, thread is thick, etc.).
2. Thread 1 The shuttle or the driver has
often scratches.
breaks or 2 The needle hole guide has scratches.
synthetic 3 The needle strikes the work clamp
fiber thread foot.
splits finely. 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 generated on the needle.
3. The needle 1 The needle is bent.
often 2 The needle hits the work clamp foot.
breaks. 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)
4. Threads 1 The counter knife is dull.
are not 2 The difference in level between the
trimmed. needle hole guide and the counter
knife is not enough.
3 The moving knife has been improperly
positioned.
4 The last stitch is skipped.
(Bobbin thread
only) 5 Bobbin thread tension is too low.
5. Stitch 1 The motions of the needle and shuttle
skipping are not properly synchronized.
often 2 The clearance between the needle
occurs. and shuttle is too large.
3 The needle is bent.
4 The driver excessively bends the needle.
Cause
– 135 –
Corrective measures
™ Adjust the clearance between the needle
and the shuttle to 0.05 to 0.1 mm.
™ Set the sewing machine so that the sewing
speed is lowered at the beginning of sewing.
™ Correct the thread tension release timing of
the thread tension controller No. 2.
™ Increase the tension of the thread take-
up spring, or decrease the tension 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 according
to the material.
™ Correctly position the needle and the
shuttle.
™ Widen the distance between the needle
and the wiper. (16 to 18 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.
™ Increase the bobbin thread tension.
™ Correct the positions of the needle and
shuttle.
™ Correct the positions of the needle and
shuttle.
™ Replace the bent needle.
™ Correctly position the driver.
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