JUKI MO-6800S Series Engineer's Manual page 66

WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the sewing machine.
Trouble
14. Double chainstitch needle
thread is loose.
15. Uneven overlocking stitches
The knotting position of the up-
per and lower looper threads
varies as shown below.
16. Uneven double chainstitches
Cause (1)
14-1) Thread tension 1-A)
14-2) Thread cam 2-A)
2-B)
14-3) Needle 3-A)
14-4) Double chainstitch 4-A)
needle thread take-
up guide
15-1) Looper thread ten- 1-A)
sion
15-2) Looper thread take- 2-A)
up
15-3) Knife width 3-A)
15-4) Thread path 4-A)
15-5) Presser foot 5-A)
15-6) Thread stand 6-A)
16-1) Thread tension 1-A)
16-2) Presser foot 2-A)
2-B)
Cause (2)
The looper thread tension is too high,
and the needle thread tension is too low.
The thread cam draws out an insuffi-
cient amount of thread.
The thread cam timing is bad.
The needle is too thin for the thread used.
Drawing amount of the needle thread is
insufficient.
The upper and lower looper thread ten-
sions are not enough.
The looper thread take-up (left) is too
high.
The knife width is unsuited for the over-
edging width.
Scratches on the thread path catch
thread.
The presser foot cones into contact
unevenly with the throat plate and feed
dogs and tends to meander.
Thread dose not come out smoothly.
The looper thread tension is not
enough.
The presser foot comes into contact
with the throat plate unevenly.
The presser foot pressure is not
enough.
Checking order and adjusting procedure
Reduce the looper thread tension to a minimum,
and increase the needle thread tension.
Refer to the pertinent Standard Adjustment.
Refer to the pertinent Standard Adjustment.
Replace the needle with a proper one.
Refer to the pertinent Standard Adjustment.
Slighrly increase the upper and lower looper
thread tensions.
Slightly lower the looper thread take-up (left).
Make the overedging width slightly smaller than
that given for the knife width.
Check the thread path for scratches.
Make the presser foot come into contact with
them evently.
Make the thread come out smoothly.
Slightly increase the tension.
Make the presser foot come into contact with the
throat plate evenly.
Increase the presser foot pressure.