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Blade point of the hook is defective.
The needle vibrates during sewing.
The time when the needle and bobbin
threads go over the hook is too late. As a
result the threads break under the hook.
The sewing machine fails to perform
sewing with consistency because of
excessively low thread tension.
Same causes as "I-1) Stitches are not
properly formed."
Presser foot components are defective.
The needle thread tension is insufficient.
The thread take-up spring has been
improperly adjusted.
The bobbin case holder stopper is
defective.
1-2)
The thread breaks when the needle
reaches the lowest position of its
stroke.
(Lower cloth)
1-3)
Miscellaneous
Thread breakage occurs when sewing
joining section between scallops
The needle thread tension is too low.
The stroke of the thread take-up spring is
too small.
The tension of the thread take-up spring is
too low.
The tension provided by the pre-tension disk
is too low.
The bobbin case holder stopper is positioned
too near to the needle.
The needle slot in the presser foot is located
this side of the needle slot in the throat plate.
The presser foot rises.
Recess on the sole of the presser foot is
smaller for the stitch length employed.
The stroke of the thread take-up spring is
too small.
Tension of the thread take-up spring is too
1ow.
Correct the blade point of the hook or replace the hook with a
new one.
Adjust the needle guard so that it works more effectively.
Increase the needle thread tension. Then balance the tension
of needle and bobbin threads.
Lengthen the stroke of the thread take-up spring.
Increase the tension of the thread take-up spring.
Increase the tension provided be the pre-tension disk.
Adjust the position of the bobbin case stopper by moving it away
from the needle.
Set the thread tension at a higher value. (For reference, 65 g for
the needle thread and 25 g for the bobbin thread)
Replace the presser foot with a new one, or correct the presser
bar.
Return the micro-lifting mechanism to the home position, or
readjust the position of the presser bar bracket.
Replace the presser foot with a new one.
Increase the needle thread tension.
Maximize the distance between the bobbin case and the hook
as long as the bobbin case does not rotate.
2. Stitch skipping
3. Isolated idling loops
Trouble
Description
Cause 1
Cause 2
Corrective measure and adjusting procedure
