JUKI DLN-6390 Engineer's Manual page 35

Adjustment Procedures
For DLN-6390 Series, bobbin case with idle-protection spring is
used. Perform the points below to adjust the pressure of the idle
prevention spring.
When bobbin runs idle.
When stitches are not
well tightened.
1) Adjusting the pressure of idle-protection spring
1 When the idling amount of the bobbin is excessive at the
time
of thread trimming, raise idle-protection spring 1 in the bobbin
case and adjust the idling amount within the range where
the
sewing is not affected.
2 Insert an old sewing machine needle or the like into the bobbin
case and remove the spring so as to raise it as shown in the
figure.
3 Adjust the pressure of the spring by changing the height of
the spring.
(Be careful that the height of the spring is as parallel as
possible.)
4 When setting the spring, first, put one of ears and put the
other ear in the state that the center section of the spring is
raised. (Be careful that the spring is not deformed.)
* Part No. of bobbin case spring : G181687500E
2) Setting the bobbin into the bobbin case
1 Pass the thread through thread slit A, and pull the thread in
the direction of arrow mark F. By so doing, the thread will
pass under the tension spring and come out from notch B.
2 Check that the bobbin rotates in the direction of arrow mark
D when bobbin thread C is pulled.
3 Securely insert the bobbin case into the hook until the end of
the hook is reached in the state that bobbin thread is pulled
out approximately 20 mm from the bobbin case.
(Caution) 1. When waste thread or cloth dust infiltrates
in section E (between bobbin case and
bobbin), and disturbs the rotation of bobbin,
unexpected sewing trouble will be caused.
Remove waste thread or cloth dust gathered
inside the bobbin periodically when
replacing the bobbin or the like.
2. When sewing is performed in the state that
the bobbin case is not securely inserted into
the hook, unexpected troubles may be
caused. When setting the bobbin case to
the hook at the time of replacement of
bobbin or the like, securely insert the
bobbin case into the hook until the end of
the hook is reached.
Increase the pressure of idle-
a
protection spring.
Decrease the pressure of
a
idle-protection spring.
31
Results of Improper Adjustment