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31. 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 is caught with the
feed dog.
5. Thread slips off the needle
eyelet simultaneously with
thread trimming.
6. Thread slips off the needle
eyelet at the start of
sewing.
7. Thread is not cut sharply.
8. Thread remains uncut after
thread trimming.
(Bobbin thread trimming
failure when stitch length
is comparatively short.)
9. 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 finished.
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.
7 Insufficient lubrication
1 Stroke of the thread take-up spring is
small.
2 Tension of the thread take-up spring is low.
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 fine 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 "24. ADJUSTING THE BOBBIN CASE
OPENING LEVER".
™ Refer to "22. NEEDLE-TO-HOOK RELATION".
™ Adjust the amount of oil in the hook properly.
Refer to "10. LUBRICATION".
™ Increase the needle thread tension.
™ Decrease the tension of the spring and increase
the stroke of the spring.
™ Refer to "22. NEEDLE-TO-HOOK RELATION".
™ Refer to "22. NEEDLE-TO-HOOK RELATION".
™ Tighten the presser spring regulator.
™ Refer to "22. NEEDLE-TO-HOOK RELATION".
™ Refer to "23. 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 fine emery paper or
buff it up.
™ Replace the bobbin or hook with a new one.
™ Refer to "24. ADJUSTING THE BOBBIN CASE
OPENING LEVER".
™ Increase the bobbin thread tension.
™ Decrease the tension applied to the bobbin
winder.
™ Perform lubrication to the hook.
(When using thick thread, it is recommended to
perform lubrication to the hook every time the
bobbin is replaced.
™ Increase the stroke of the thread take-up spring.
™ Increase the tension of the thread take-up spring.
™ 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 "25. 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 "18. THREAD TENSION".
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Corrective measures
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