JUKI DLN-6390 Engineer's Manual page 42

Troubles
From the previous page
1-4) Length of bobbin thread at
1-5) Knotting of needle and
1-6) Bobbin thread position is
1-7) Initial position of the needle
1-8) Position of the needle hole
2-1) Needle thread remaining on
2. End of needle thread
comes out on the
cloth at the start of
sewing
3. Wrong side of cloth
at the start of sewing
is dirty. (Long needle
t h r e a d r e m a i n s
under the cloth.)
4-1) Length of needle thread
4. Thread slips off from
needle at the start of
s e w i n g . N e e d l e
thread slips off from
needle immediately
4-2) Same causes and
a f t e r t h r e a d
trimming.
Cause (1)
the start of sewing is too
short.
bobbin threads at the start
of sewing is difficult.
unstable.
bar is improper.
is improper.
the needle tip after thread
trimming is too long.
remaining on the needle tip
after thread trimming is
uneven.
corrective measures as
those of Trouble of "1.
Stitch skipping of 1 to
several stitches occurs at
the start of sewing"
To the next page
Cause (2)
4)-A Bobbin runs idle and end
of bobbin thread is drawn
in bobbin case.
4)-B There is a scratch on
hook and bobbin thread
is cut on the way.
4)-C Counter knife excessively
p r o t r u d e s . ( N e a r t o
needle)
5)-A Speed at the start of
sewing is too fast, and
n e e d l e a n d b o b b i n
threads are difficult to be
interlaced.
6)-A There is no groove for
guiding bobbin thread in
the inner hook.
7)-A Needle rocking position is
on the operator's side
and pressing stitches with
presser is too late.
8)-A Position of throat plate is
improper and the needle
hole in terms of needle
rocking position is located
on the antioperator's
side. As a result, presser
is slow to press stitches.
1)-A Tension of thread tension
No. 1 is too low.
1)-B Thread trimming timing is
too late.
1)-C C o u n t e r k n i f e i s
excessively receded.
1)-A Tension of thread tension
No. 1 is made too high
and thread is cut before
moving knife and counter
knife engage with each
o t h e r s i n c e t h r e a d
trimming timing is too
late. (Trimming on the
way)
1)-B Receding amount of
m o v i n g k n i f e i s
insufficient and there is a
c a s e w h e r e n e e d l e
thread is not caught by
thread draw-out of the
knife unit.
1)-C Blade of counter knife is
too sharp and trimming
on the way occurs.
38
Corrective measures
Increase the spring pressure of idle-
protection spring.
Increase bobbin thread tension.
Correct the scratch on the hook or
replace the hook.
Correct the position of counter knife
according to 4-(7).
Decrease of the number of revolutions of
soft-start.
Increase the number of stitches of soft-
start.
* Normally one stitch per 500 rpm is set.
Check whether there is the groove for
guiding bobbin thread in the hook. If not,
replace the hook with one for thread
trimming.
Adjust the initial position of the needle
bar according to 4-(14).
Correctly fix the position of throat plate
according to 4-(4).
Increase the tension of thread tension
No. 1.
Correct the thread trimmer timing
according to 4-(6).
Correct the position of counter knife
according to 4-(7).
Perform thread trimming by hand with the
procedure described in 4-(6) and stop at
UP stop position. At this time, when the
length of needle thread remaining on the
needle tip is shorter than 10 mm as
compared with the length when
performing thread trimming by pedal
operation, it is thread trimming on the
way. Properly adjust the thread trimming
timing according to 4-(6) and decrease
the tension of thread tension No. 1.
Correct the receding amount of moving
knife according to 4-(4).
Resharpen the counter knife according
to 6-(1) or replace the counter knife.