46
23. TROUBLES IN SEWING AND CORRECTIVE MEASURES
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 “17. NEEDLE-TO-HOOK
RELATION.”
™
Adjust the amount of oil in the hook
properly.
Refer to “5. LUBRICATION”.
™
Increase the needle thread tension.
™
Decrease the tension of the spring and
increase the stroke of the spring.
™
Refer to “17. NEEDLE-TO-HOOK
RELATION.”
™
Refer to “17. NEEDLE-TO-HOOK
RELATION.”
™
Tighten the presser spring regulator.
™
Refer to “17. NEEDLE-TO-HOOK
RELATION.”
™
Replace the needle with one which is
thicker than the current needle by one
count.
™
Refer to “7. THREADING THE BOBBIN
THREAD”.
™
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.
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
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
Improper type of needle is used.
1
Bobbin thread does not pass through
the tension spring of the bobbin case.
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
Needle tip is worn out.