－37－
9. BAD SEWING CONDITION & ITS CAUSE AND REMEDY
[NOTE]
Please fix the troubles during the sewing machine operation with referring to the
following instructions.
Beside, if the trouble conditions are not coming under these classification, please
contact the sewing machine dealers nearby.
Bad condition Cause Remedy
Ref. page
& Item
Poor thread quality Use better quality thread
----
Tight upper thread tension Adjust thread tension
6-3
Strong thread take up spring
Adjust thread take up spring
properly
7-13
Upper thread is thicker than
needle size
Change needle to suitable
size
----
Damages on shuttle hook or
driver
Change them new ones or
grind them with buffing wheel
or grind stone
----
Damages inside presser foot
needle hole
Change it new one or grind it
with buffing wheel
----
Needle and shuttle hook are not
in proper timing
Adjust the timing
----
Slow down sewing speed
6-2(5)
Use silicon oil
----
1.
Upper thread
breakage often
happens
Thread melts with needle heat
Use needle cooler
----
Thread tension discs are not
opened at trimming
Adjust thread tension release
7-16
Thread take up spring swings too
much
Adjust thread take up spring’s
swing stroke
7-12
Upper thread is broken before
regular trimming
Adjust fixed knife and needle
plate position
7-11
Needle size is bigger than thread
size
Change needle to suitable
size
----
Pre-tension is too tight Adjust pre-tension
7-14
Thread guide is in wrong position
Adjust thread guide position
properly
7-5
Needle and shuttle hook are in
bad timing
Adjust the position properly
7-2
Adjust trimmer cam position
7-9
Adjust movable knife position
7-10
2.
Upper thread
is pulled out
from needle
Trimmer timing is not correct
Adjust synchronizer position
7-17
Too short bobbin thread by
bobbin spinning at trimming
Use non racing spring with
bobbin
----
Bobbin thread tension is too tight
Loosen bobbin thread tension
spring
6-3(1)
Decrease pre-tension
7-14
Adjust trimmer cam position
7-9
Adjust synchronizer position
7-17
Make thread take up swing
stroke smaller
7-12
Advance thread tension
release timing
Control unit
Adjust thread guide position
properly
7-5
3.
Skip stitch
happens at
start sewing
Thread tail from needle is very
short after trimming
Thread tail from needle is very
short after trimming
Decrease pre-tension
7-2
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