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25. TROUBLES IN SEWING AND CORRECTIVE MEASURES
Troubles
1. Thread breakage
(Thread frays or is worn
out.)
(Needle thread trails 2 to
3 cm from the wrong side
of the fabric.)
2. Stitch skipping
3. Loose stitches
4. Thread slips off the needle
eyelet simultaneously with
thread trimming.
5. Thread slips off the
needle eyelet at the start
of sewing.
6. Thread is not cut sharply.
7. Thread remains uncut
after thread trimming.
8. Stitch skipping occurs at
the start of sewing after
thread trimming.
46
Causes
1 Thread path, needle point, hook
blade point or bobbin case resting
groove on the throat plate has sharp
edges or burrs.
2 Needle thread tension is too high.
3 Needle comes in contact with the
blade point of hook.
4 Amount of oil in the hook is too small.
5 Needle thread tension is too low.
6 Thread take-up spring works
excessively or the stroke of the
spring is too small.
7 Timing between the needle and the
hook is excessively advanced or
retarded.
1 Timing between the needle and the
hook is excessively advanced or
retarded.
2 Pressure of the presser foot is too low.
3 The clearance provided between the
top end of the needle eyelet and the
blade point of hook is not correct.
4 Hook needle guard is not functional.
5 Improper type of needle is used.
1 The bobbin thread has not been
passed through the bobbin case
tension spring.
2 Thread path has been poorly
fi nished.
3 Bobbin fails to move smoothly.
4 Bobbin thread tension is too low.
5 Bobbin has been wound too tightly.
6 The needle tip is blunt.
1 Thread tension given by the tension
controller No. 1 is too high.
2 A hard-to-slip thread is used.
1 Thread tension given by the tension
controller No. 1 is too high.
2 Bobbin thread tension is too low.
1 The thread trimming timing is wrong.
2 The knives have blunt blades.
3 The knife pressure is too low.
1 The position of the rotary knife is
inaccurate.
2 The thread trimming timing is wrong.
1 The length of remaining bobbin
thread is too short.
Corrective measures
™ Remove the sharp edges or burrs on
the blade point of hook using a fi ne
emery paper. Buff up the bobbin case
resting groove on the throat plate.
™ Decrease the needle thread tension.
™ Refer to "18. NEEDLE-TO-HOOK
RELATION".
™ Adjust the amount of oil in the hook
properly.
Refer to "6. LUBRICATION".
™ Increase the needle thread tension.
™ Decrease the tension of the spring and
increase the stroke of the spring.
™ Refer to "18. NEEDLE-TO-HOOK
RELATION".
™ Refer to "18. NEEDLE-TO-HOOK
RELATION".
™ Tighten the presser spring regulator.
™ Refer to "18. NEEDLE-TO-HOOK
RELATION".
™ Refer to "18. NEEDLE-TO-HOOK
RELATION".
™ Replace the needle with one which is
thicker than the current needle by one
count.
™ See "8. THREADING THE BOBBIN
CASE".
™ Remove rough parts with a fi ne emery
paper or buff it up.
™ Replace the bobbin or hook with a new
one.
™ Increase the bobbin thread tension.
™ Decrease the tension applied to the
bobbin winder.
™ Replace the needle.
™ Decrease the thread tension given by
the tension controller No. 1.
™ Decrease the number of times of
threading the needle thread.
™ Decrease the thread tension given by
the tension controller No. 1.
™ Increase the bobbin thread tension.
™ See "19. ADJUSTING THE THREAD
TRIMMING".
™ Replace the rotary knife and counter
knife with new ones, or correct the
current ones.
™ See "19. ADJUSTING THE THREAD
TRIMMING".
™ See "19. ADJUSTING THE THREAD
TRIMMING".
™ See "19. ADJUSTING THE THREAD
TRIMMING".
™ Decrease the bobbin thread tension.
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