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27. 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.
(Bobbin thread trimming
failure when stitch length
is comparatively short.)
8. Thread breaks at the start
of sewing after thread
trimming.
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 Bobbin case opening lever provides an
excessive clearance at the bobbin case.
4 Needle comes in contact with the blade
point of hook.
5 Amount of oil in the hook is too small.
6 Needle thread tension is too low.
7 Thread take-up spring works excessively or
the stroke of the spring is too small.
8 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 Bobbin thread does not pass through the
tension spring of the inner hook.
2 Thread path has been poorly fi nished.
3 Bobbin fails to move smoothly.
4 Bobbin case opening lever provides too
much clearance at the bobbin.
5 Bobbin thread tension is too low.
6 Bobbin has been wound too tightly.
1 Thread tension given by the tension
controller No. 1 is too high.
1 Thread tension given by the tension
controller No. 1 is too high.
2 Clamp spring has improper shape.
3 Bobbin thread tension is too low.
1 The blades of moving knife and counter
knife have been improperly adjusted.
2 The knives have blunt blades.
3 Bobbin thread tension is too low.
1 Initial position of the moving knife has been
improperly adjusted.
2 Bobbin thread tension is too low.
1 The needle thread is caught in the hook.
™ 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.
™ Decrease the clearance provided between
the bobbin case opening lever and the
bobbin.
Refer to "20. ADJUSTING THE BOBBIN
CASE OPENING LEVER".
™ 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 "19. ADJUSTING THE HOOK
NEEDLE GUARD".
™ Replace the needle with one which is thicker
than the current needle by one count.
™ Thread the bobbin thread correctly.
™ Remove rough parts with a fi ne emery paper
or buff it up.
™ Replace the bobbin or hook with a new one.
™ Refer to "20. ADJUSTING THE BOBBIN
CASE OPENING LEVER".
™ Increase the bobbin thread tension.
™ Decrease the tension applied to the bobbin
winder.
™ Decrease the thread tension given by the
tension controller No. 1.
™ Decrease the thread tension given by the
tension controller No. 1.
™ Replace the clamp spring with a new one or
correct the current one.
™ Increase the bobbin thread tension.
™ Refer to "21. POSITION OF THE COUNTER
KNIFE AND ADJUSTMENT OF THE KNIFE
PRESSURE".
™ Replace the moving knife and counter knife
with new ones, or correct the current ones.
™ Increase the bobbin thread tension.
™ Refer to the Engineer's Manual.
™ Increase the bobbin thread tension.
™ Shorten the length of thread remaining on
the needle after thread trimming.
Refer to "14. THREAD TENSION".
– 62 –
Corrective measures
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