Malfunctions
Causes
Order
of
Inspection
and
Corrective
Measures
Needle thread slips out from
the
needle
immediately
after
trimmin;*
* Hie fixed knife is too sharp (too pointed at top) cutting
the
thread
only
with
the
fixed
knife
* Knife thread guide, moving knife and hook are bruised
* C^m
timing
is
too
fast so even the
needle
thread
on
the
side
of
the
needle
is
trimmed
also
'
Needle
is
too
thick
®
When
the
length
is
less
than
20mm(25/32"),
adjust
the
position
of the
bobbin
presser
(IV—7).
®
When
the
needle
thread
breaks
just after
trimming,
this is
because
the
needle
thread
remaining
at the side of the needle is being cut due to the inadequate
disposition of the thread by the moving knife.
When
the needle plate is removed,
about 20mm(25/32") of the needle thread is
remaining.
In such a case,delay the
timing
of
the
cam
(IV-1).
C. At the
start
of
sewing,
the
tip
of
needle
tluead
sticks
out
atop
the
cloth
1.
The
needle
thread
remain
ing at the needle
eye
after
thread trimming is too long
*
The
first
tension
disc
tension
is
too
weak
* Cam timing is too
late
*
The
fixed
knife
is
retreated
too
far
® Try strengthenthe first tensiondisc (lV-2).
(D Try
bring
the
fixed
knife
closer
to the
needle
(lV-3).
(D Try
quickening
the cam timing(IV-1).
D.
The
back
side
of
the
cloth
is
dirty
at
the
start
of
sewing
(Long
needle
thread
is
remaining
under
the
cloth)
1.
Tlie
needle
thread
remain
ing at
needle
eye
after
trimming is too long
2. Needle, needle
plate
and
presser foot inadequate
and after trimming, can
not
shorten
the
remain
ing
needle
thread
at
needle
tip
(Please refer to previous chapters)
0 Refer to
previous
chapter.
(D
Refer
to
1-2
chapter
on
"Malfunctions
and
corrective
measures"
and
make
proper
adjustments.
I-;.
Thread
tension
is
bad
at
start
of
sewing
1.
The
needle
tluead
tension
at start of sewing too
weak
• Inadequate installation of bobbin presser.
• Due to idle spinning
of
the bobbin, the tension
of
the bobbin
thread
is
weakened.
a.
Tlic
tension
of
the
bobbin
thread
loo
weak
•
Both
needle
thread
and
bobbin
thread
tensions
arc
too
weak
• The prc.vwr fool and the needle plate arc
not
suitable.
CO
Adjustthe installedpositionof bobbin
presser.
(2)
Inspect
the
presser
foot
and the
needle
plate
closely
and
refer
to
1-2
para
for
adjustment.
®
Take
out the
bobbin
case
after
(rimming
and as you
push
the
bobbin,
try
pulling
out the bobbin thread. If the tension is weak, strengthen the bobbin thread tension.
®
Make
the needlethread tensionstronger.
(D Increase the pressureof presserfoot.
(D
Use
a bobbincasewitha
spring.
F.
Needle
thread
cannot
be
cut
(bobbin
tlircad
is
cut)
1. Skip stitching at the end
of sewing cycle
•
Defective
needle
insertion
• Stroke of take-up spring too big
• Timing
of
sewing
hook
bad
0
Correct
the
installed
angle
of the
needle
and
change
the
curved
needle.
®
Make
the
stroke
of the
take-up
spring
smaller
(5~7mm).
0
Inspect
the
skip-stitching
at
low
speed
and
correct
the
timing
of
the
sewing
hook
(Make
the
timing
of the
sewing
hook a little
quicker
than
normal
lockstitching
machine).
2. One
part
of
blade
of
trimming knife
docs
not
cut
well
• The trimming
parts
of
moving knife and fixed knife arc
not sticking together at trimming time.
(The angle of the fixed knife, its position and the slant
of the cutting point are not matched with the cutting part
of moving knife.
Remove
the needle plate, and
move
the knife with your hand and try cutting the
#50 cotton thread (3 strands at the same time). If the 3 threads are cut evenly,
it's
adequate
but
if
not:
(V Sharpen the fixed knife blade (IV-5).
0
Correct
the
inclined
angle
of the tip of the
fixed
knife
(IV-5).
@ Re-adjust the installed position of the fixed knife (IV-3).
29
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