(3) Thread trimming failure
Phenomenon
Possible
causes
Even after a seam has been completed, either or
both
the
needle and bobbin threacl are
not
trimmed
off
or an excessively long or short needle thread is left in the needle eye after
trimming.
•Thread
trimmer knife is
not
sharp enough.
•Moving knife is
too
far from the needle plate needle hole guide.
•Moving knife is
not
properly adjusted.
•Position
of
the
shuttle race spring is
not
correct.
•The
last stitch is skipped.
Corrective
measures
1) Thread trimmer knife is not sharp enough.
A.
If
either the moving or counter knife blade is worn
out
after
a long period
of
use or if a newly installed moving knife
does not redch the cutting point over the counter knife, the
thread trimmer knife will fail to
cut
sharply.
Usually, the sharpness
of
the blade will increase after it has
been
used
for
a
while.
B. The correct position
of
each thread trimmer component
a. Height
of
the counter knife (Fig. 34-a)
b. Difference in height between the counter knife and the
needle plate needle hole guide.
The
counter
knife
must
be 0.1 to 0.15 mm higher
than
the needle plate needle hole guide (Fig. 34-b).
c. Difference in height between the moving knife and the
needle plate needle hole guide.
The lowest point
of
the moving knife is 0.15 mm lower
than the highest point
of
the needle plate needle hole
guide (Fig. 34-b).
This adjustment can be made by inserting a washer
of
suitable
thickness.
Part
No.
Description
Thickness
B2423-280-00A
Washer (for moving knife)
0.4
mm
B2423-280-00B
Washer(for moving knife)
0.5
mm
B2423-280-00C
Washer (for moving knife)
0.6
mm
B2423-280-00D
Washer (for moving knife)
0.7
mm
d. The moving knife shakes up and down
too
much.
Normally, the moving knife shakes from 0.05 to 0.1 mm
at its
top
end.
C.
If
the right
thread
is
not
trimmed;
Adjust the counter knife by slightlyloweringits top end.
(See Fig. 34-a; lessenthe difference
of
0.2 mm.)
D.
If
the
left
thread
is
not
trimmed:
Adjust the counter knife by slightly raisingits top end.
(Note) Gently bend the counter knife for the above C and D
adjustment takingcarenot to break it. (Fig.34-c)
-
18
-
Counter
knife
Needle
plate
Counter
knife
Moving
knife
I S
Fig.
34-a
Needle
plate
needle
Needle
plate
hole
guide
Fig.
34-b
Counter
knife
Left
thread
Moving
knife
connecting
link
Right
thread
Needle
plate
needle
hole
guide
Moving
knife
Fig.
34-c
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