JUKI MO-6800S Series Engineer's Manual page 25

Adjustment procedures
1) Returning amount of the double chain looper
Loosen clamping screw ❷ of double chain lopper driving arm ❶
to make this adjustment.
2) Longitudinal motion (Avoid motion)
1. Open the rear cover ❻ of the sewing machine.
2. Loosen the screw ❽ slightly.
3. Turn the eccentric pin ❼ to make adjustment.
To increase the longitudinal motion A, turn the eccentric pin ❼ to
⊕ direction.
To decrease the longitudinal motion A, turn the eccentric pin ❼
to ⊖ direction.
(Caution) Depending on the initial direction of the eccentric pin
❼ , the adjustment direction becomes opposite.
<Distance between eccentric pin ❼ and screw ❽ >
When the distance is minimum :
The longitudinal motion A becomes maximum. To
whichever direction you turn, the longitudinal mo-
tion A decreases.
When the distance is maximum :
The longitudinal motion A becomes minimum. To
whichever direction you turn, the longitudinal mo-
tion A increases.
4. Tighten the screw ❽ after the adjustment.
5. At the end of the adjustment, close the rear cover ❻ .
3) Clearance between the double chain looper and the needle
1. Loosen clamping screw ❷ of double chain lopper driving arm ❶ .
2. Turn fine-adjustment screw ❺ to adjust the clearance by moving
double chain lopper driving arm ❶ back and forth.
Adjust so that the clearance of 0 ± 0.05 mm is provided between
crest B of the lower end of scarf of double chainstitch needle ❹
and double chain looper ❸ .
At this time, the tip of double chain looper ❸ should be located
inside the side face of double chainstitch needle ❹ .
Results of Improper adjustment
Excessive returning amount
o
of the double chain looper will
cause frequent stitch skipping
when filament thread is used.
Insufficient returning amount
o
of the double chain looper will
cause frequent needle thread
stitch skipping when a spun
thread is used.
If the avoid motion is too large,
o
triangle stitch skipping will often
occur.
Insufficient avoid motion will
o
cause the needle tip to hit the
looper, producing scratches on
the needle tip or looper.
Excessive clearance will cause
o
frequent needle thread stitch
skipping.
Insufficient clearance will cause
o
to looper to hit the needle,
leading to needle breakage or
scratches on the blade point of
looper with consequent needle
thread breakage.
– 13 –
Bad needle
entry
Good needle
entry