27.
TROUBLES
IN
SEWING
AND
CORRECTIVE
MEASURES
Troubles
Causes
Corrective
measures
1.
Thread
breakage
(Thread frays or is worn
out.)
(Needle
thread
trails 2 to
3 cm from
the
wrong side
of
the
fabric.)
® Thread path, needle point,hook blade point
or bobbin
case
resting
groove
on
the
throat
plate
has
sharp
edges
or
burrs.
(D Needlethread tension is too high.
(D Bobbin
case
opening lever provides an
excessive
clearance
at
the
bobbin
case.
® Needle comes incontact withthe blade point
of
hook.
(D Amount of oil in the hook is too small.
® Needle thread tension is too low.
® Thread take-upspringworksexcessivelyor
the stroke of
the
spring is too small.
®
Timing
between the needle and the hook is
excessively
advanced
or
retarded.
o Remove the
sharp
edges
or burrs on the blade
point of hook using a fine emery paper. Buffup
the
bobbin
case
resting groove on ttie
throat
plate.
o
Decrease
the
needle
thread
tension.
0
Decrease
the
clearance
provided
between
the
bobbin
case
opening lever
and
the
bobbin.
Refer
to
"20.
ADJUSTING
THE
BOBBIN
CASE
OPENING
LEVER".
o
Refer
to
"18.
NEEDLE-TO-HOOK
RELATION".
0 Adjust
the
amount
of oil in the hook properly.
Refer
to
"6.
LUBRICATION".
o
Increase
the
needle
thread
tension.
o Decrease the tension of the spring and increase
the stroke of the spring.
o
Refer
to
"18.
NEEDLE-TO-HOOK
RELATION".
2. Stitch skipping
®
Timing
between the needle and the hook is
excessively
advanced
or
retarded.
® Pressure of the presser foot is too low.
d) Theclearance
provided
betweenthe top end
of the
needle
eyelet
and
the
blade
point of
hook
is
not
correct.
@ Hookneedle guard is not functional.
® Improper type of needle is used.
o
Refer
to
"18.
NEEDLE-TO-HOOK
RELATION".
o Tighten the
presser
spring regulator,
o
Refer
to
"18.
NEEDLE-TO-HOOK
RELATION".
o
Refer
to
"19.
ADJUSTING
THE
HOOK
NEEDLE
GUARD".
o
Replace
the
needle
with
one
which is thicker
than
the
current
needle
by
one
count.
3.
Loose
stitches
(D Bobbinthread does not pass through the
tension spring of the inner hook.
(D Thread path has been poorlyfinished.
®
Bobbin
failsto movesmoothly.
®
Bobbin
case openingleverprovidestoomuch
clearance
at
the
bobbin.
® Bobbin
thread
tension is too low.
® Bobbinhas been wound too
tightly.
o
Thread
the bobbin
thread
correctly.
0
Remove
rough
parts
with a fine
emery
paper
or
buff it up.
0
Replace
the
bobbin or
hook
with a
new
one.
0
Refer
to
"20.
ADJUSTING
THE
BOBBIN
CASE
OPENING
LEVER",
o
Increase
the
bobbin
thread
tension.
o
Decrease
the
tension
applied
to
the
bobbin
winder.
4.Thread
slips
off
the
needle
eyelet
simultaneously
with
thread
trimming.
® Thread tension givenbythe tensioncontroller
No. 1 is too high.
0
Decrease
the
thread
tension given by
the
tension
controller
No.
1.
5.Thread
slips
off
the
needle
eyelet
at the
start
of sewing.
® Threadtension
given
bythe tension
controller
No. 1 is too high.
@ Clampspringhas improper shape.
® Bobbin
thread
tension is too low.
o
Decrease
the thread tension given by the tension
controller
No.
1.
o
Replace
the
clamp
spring
with a
new
one
or
correct
the
current
one.
o
Increase
the
bobbin
thread
tension.
6.
Thread
is not cut sharply.
® The blades of
moving
knife
and counter
knife
have
been
improperly adjusted.
®
The
knives
have
blunt blades.
® Bobbin
thread
tension is too low.
o
Refer
to
"21.
POSITION
OF
THE
COUNTER
KNIFE
AND
ADJUSTMENT
OF
THE
KNIFE
PRESSURE".
o
Replace
the
moving knife
and
counter
knife with
new
ones,
or
correct
the
current
ones,
o
Increase
the
bobbin
thread
tension.
7.
Thread
remains
uncut
after thread trimming.
(Bobbin
thread
trimming
failure
when
stitch length
is comparatively short.)
0
Initial
positionof the
moving
knife
has been
improperly
adjusted.
® Bobbin
thread
tension
is too low.
o Refer to the Engineer's Manual,
o
Increase
the
bobbin
thread
tension.
8.
Thread
breaks
at
the
start
of
sewing
after
thread
trimming.
0 The needle thread is caught inthe hook.
o
Shorten
the
length of
thread
remaining on
the
needle
after thread trimming.
Refer
to
"14.
THREAD
TENSION".
50
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