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1-13. Troubles and corrective measures (Sewing conditions)
Trouble
① Stitches are slipped at the start.
1. The needle
thread slips off
at the start of
bar-tacking.
② The needle thread remaining on
③ The bobbin thread is too short.
④ Needle thread tension at 1st
⑤ Thread clamp is unstable
⑥ Pitch at 1st stitch is too small.
① The shuttle or the driver has
2. Thread often
breaks or
synthetic fiber
② The needle hole guide has
thread splits
finely.
③ The needle strikes the
④ Fibrous dust is in the groove of
⑤ The needle thread tension is too
⑥ The tension of the thread take-up
⑦ The synthetic fiber thread melts
⑧ When taking up thread, thread is
① The needle is bent.
3. The needle
often breaks.
② The needle strikes the
③ The needle is too thin for the
④ The driver excessively bends the
① The counter knife is dull.
4. Threads are not
trimmed.
② The difference in level between
③ The moving knife has been
④ The last stitch is skipped.
(Bobbin thread only)
⑤ Bobbin thread tension is too low.
⑥ Flopping of cloth
Cause
the needle after thread trimming
is too short.
stitch is too high.
(material is apt to be expanded,
thread is hard to slide, thread is
thick, etc.).
scratches.
scratches.
intermediate presser foot.
the shuttle race.
high.
spring is too high.
due to heat generated on the
needle.
pierced with needle tip.
intermediate presser foot.
material.
needle.
the needle hole guide and the
counter knife is not enough.
improperly positioned.
Corrective measures
◦ Adjust the clearance between the needle
and the shuttle to 0.05 to 0.1 mm.
◦ Set soft-start sewing at the start of
bartacking.
◦ 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 rpm)
◦ 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 intermediate
presser 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.
◦ Lower the needle bar height from the
engraved marker line by a half of the
line to as much as the line.
◦ Check the rough state of needle tip.
◦ Use the ball-pointed needle.
◦ Replace the bent needle.
◦ Correct the position of the intermediate
presser foot.
◦ Replace it with a thicker needle
according to the material.
◦ Correctly position the needle and the
shuttle.
◦ 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.
◦ Lower the intermediate presser height
of the last stitch.
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