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Trouble
10. Irregular stitch
Thread knots appear on either
side of material at random.
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Cause (1)
10-1) The matters related to the
hook are inappropriate.
10-2) The bobbin or bobbin case is
defective.
10-3) The needle or bobbin thread
tension is too low.
10-4) The thread take-up spring is
inappropriately adjusted.
10-5) The thread path is defective.
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Cause (2)
1-A) Hook oil is too large or too small
in amount.
1-B) The hook is defective. (Thread
catch, defective thread path,
etc.)
2-A) The bobbin thread cannot be
pulled out smoothly due to poor
fit between the bobbin and bob-
bin case.
2-B) Defective thread winding around
the bobbin winder causes the
bobbin thread to be caught.
2-C) The tension adjusting spring of
the bobbin case is defective.
2-D) The bobbin thread idles in the
bobbin case.
2-E) The bobbin is inserted into the
bobbin case in the wrong direc-
tion.
4-A) The stroke of the thread take-up
spring is too long or too short.
4-B) The tension of the thread take-
up spring is too high or too low.
5-A) The thread path is not smooth.
Check and corrective measures
Adjust the oil volume to the appropriate level.
Replace the hook or modify the thread path.
Replace the bobbin or bobbin case.
Correct the bobbin thread winding tension or
the position of the bobbin winding tensioner.
Replace the bobbin case.
Adjust the tension of the idling prevention
spring with reference to "3.-(4)."
Refer to "3.-(4)." Irregular stitches are correct-
ed by rotating the bobbin in the reverse direc-
tion.
Increase the tension of the needle or bobbin
thread.
Adjust the stroke of the thread take-up spring.
Adjust the tension of the thread take-up spring.
Finish the thread path appropriately.
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