Upper Thread Adjustment - SunStar SC-700A User Manual

7) Upper Thread Adjustment

(1) Main thread adjustment device
The tension of the upper thread gets tighter if the tension
adjusting nut① as in Fig. 25 is turned in a clockwise
direction and it gets looser when turned in the opposite
direction. The tension of the thread should differ
according to the sewing conditions which depend on the
material, thread, stitch length, etc. So the tension should
be adjusted as seen fit for the conditions.
(2) Tension adjustment of thread take up lever spring
As in Fig. 25, use a driver in the thread adjustment shaft
groove② to adjust the spring tension. The thread take up
lever spring grows tighter when the driver is turned
clockwise and looser when turned counterclockwise.
(3) Auxiliary thread adjuster
Turn the auxiliary thread tension adjusting nut① in
clockwise direction to make the remaining thread length
on the needle after trimming shorter and in
counterclockwise direction to make it longer, as shown
in Fig. 26. The appropriate length of the upper thread
remaining after trimming is 30~40mm.
(4) Thread release control
The thread release takes place simultaneously with the movement of the trimming solenoid. As seen in Fig. 27, the
amount of thread release is controlled by moving the fixed position of the thread release wire②, which is connected with
the clutch lever①, left and right. Loosen the two fixing nuts③ and pull the cable wire② to the left. Then fasten the nuts
③ to release the thread to a large extent. If the cable wire is pushed to the right and the nuts③ tightened, the thread
release happens on a lesser scale. After adjustment, tighten the nuts③ once again and check whether the opening of the
thread guide plate④ of the thread adjuster is about 0.5-1mm when the thread releaser is in operation. There should be no
opening when the thread releaser is not in operation; the thread guide plates④ should be touching back to back. The
moving stroke of the thread release lever① is 11mm. Adjust such that the thread guide plates④ do not open when the
cable wire is pulled about 0-8mm and that the plates open when the cable wire is pulled about 8-11mm. (See Fig. 27.)
11mm
When the upper thread is weak
When the upper thread is strong
Weaker
Proper tension of the upper thread
Stronger
Longer
Shorter
Opening 0.5~1mm
[Fig. 25]
[Fig. 26]
[Fig. 27]
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