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4. Irregular Stitches
4-1) Defective hook components
1-A) Oil in the hook is insufficient.
Adjust so that a sufficient amount of oil is supplied
Knots of the needle thread and
to the hook (Refer to [3.-(16)-4)])
the bobbin thread irregularly
appear on the front or back of
1-B) Dust gathers on the reverse side of the
Clean the inner hook.
the material.
inner hook
1-C) Hook timing is too early.
Retard the hook timing.
1-D) Defective hook (The hook has scratches
Replace the hook with a new one and/or correct
or the thread path is improper, etc.)
the thread path.
1-E) The inner hook opening lever provides
Decrease the clearance at the inner hook opening
excessive clearance.
lever.
1-F) Clearance between the throat plate and
Re-adjust the height of the hook (Refer to [3.-(5)]).
the inner hook stopper is too small.
4-2) Defective bobbin and/or inner hook
2-A) The bobbin is not engaged with the inner
Replace the bobbin or inner hook with a new one.
hook. As a result, the bobbin thread cannot
be led smoothly
2-B) Bobbin thread is not wound. As a result,
Adjust the tension of the bobbin winder or the
the bobbin thread fails to be fed smoothly.
position of the bobbin winder tension controller.
2-C) Bobbin runs idle in the inner hook.
Increase the idling prevention spring pressure.
2-D) Defective adjusting spring tension of the
Replace the inner hook with a new one.
inner hook
2-E) Thread has been wound excessively on
Re-wind the bobbin thread to the extent where the
the bobbin.
thread wound round the bobbin does not protrude
from the periphery of the bobbin.
4-3) The needle thread tension and the bobbin
Increase the thread tension.
thread tension are too low.
4-4) Thread take-up spring has not been
4-A) Stroke of the thread take-up spring is too
Re-adjust the stroke of the thread take-up spring.
correctly adjusted.
large or too low.
4-B) Tension of the thread take-up spring
Re-adjust the tension of the thread take-up spring.
is too high or too low.
4-5) Improper thread path
5-A) Thread path is not smooth on the surface.
Smoothen the thread path.
5-B) Thread path has scratches on the surface.
Smoothen the thread path.
5-C) Thread is caught in some part of the thread path.
Smoothen the thread path.
4-6) Length of thread fed by the thread take-
Move the take-up thread guide to the left and
up lever is excessive or insufficient.
right and adjust the length of the thread to be fed
by the thread take-up lever.
4-7) Improper feed timing
Re-adjust the feed timing. (Refer to [3.-(6)]).
Trouble
Cause (1)
Cause (2)
Check Procedure and Corrective Measures
Stitch
Irregular stitches on the
back of the material
Irregular stitches
on the front of the
material
Needle
Thread
Bobbin
Thread
