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Trouble
2. Thread cut at bobbin
thread looper
3. Needle breakage
4. Needle edge blunting
Cause (1)
2-1)Thread path
2-2) Adjustment of bobbin
thread cam
2-3) Thread tension
2-4) Thread
2-5) Needle heat
3-1) Needle entry
3-2) Interference between
lower looper and blin
dstitch of needle
3-3) Interference between
rear of lower looper
and needle tip
3-4) Rear needle guide
3-5) Needle size
3-6) Thread tension
3-7) Feed dog height
4-1) Needle entry
4-2) Rear needle guide
4-3) Contact with the rear
of the looper
Cause (2)
1-A)Resistance is developed
when there is a scratch,
a burr, or rust on the
throat plate, lower looper,
bobbin thread cam,
bobbin thread path pipe,
bobbin thread path guide,
or thead tension disc.
2-A)Excessive tension is
provided because of
improper timing of the
bobbin thread cam.
3-A)Excessive thread tension
4-A)Poor quality of the thread
5-A)Thread cut occurs when
the thread touches the
right needle at sewing
stop due to needle heat.
1-A)Front/rear and right/left
needle entry seems to
be awkward in conjunction
with the needle hole of
the throat plate.
2-A)The needle breaks because
of the interference between
the tip of the lower looper
and the needle.
3-A)The needle breaks because
of the strong interference
between the rear of the
lower looper and the
needle tip.
4-A)Excessive clearance
between the needle and
rear needle guide causes
needle shaking and then
interference between the
needle and the lower
looper tip resulting in
needle breakage.
5-A)For the case that the
needle is too thin for the
material that is now used
6-A)Excessive needle thread
tension
7-A)Too high feed tooth
causes needle sidewise
movement resulting in
needle breakage.
1-A)Front/rear and right/left
needle entry seems to
be awkward in conjunction
with the needle hole of
the throat plate.
2-A)Improper position of the
front-to-rear direction
3-A)Too often contact between
the rear of the lower
looper and the needle tip
– 54 –
Check and corrective measures
Take measures to remove flaws, burrs, etc., and
finish the thread path neatly.
In this case, however, the throt plate, lower
looper, bobbin thread cam, and such impor-
tant parts should be replaced if their shapes
seem to have changed.
Refer to the standard adjustment values.
Reduce the tension in consideration of the
tension balance with the needle thread.
Use a high-quality thread.
Reduce the sewing speed.
Refer to the standard adjustment values.
Adjust the lower looper to prevent the
nterference.
Refer to the standard adjustment values.
(6) Adjust the looper movement locus.
Refer to the standard adjustment values.
Adjust the clearance between the needle and
rear needle guide.
Refer to the standard adjustment values.
Use a thicker needle.
Reduce the needle thread tension.
Refer to the standard adjustment values.
Refer to the standard adjustment values.
Clearance check between rear needle guide
and needle
Refer to the standard adjustment values.
(6) Adjust the looper movement locus to make
the contact level appropriate when the lower
looper moves backward.
Refer to the standard adjustment values.
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