JUKI MO-6700D Series Manual page 58

Trouble
10. Triangle double chain needle
thread stitches are skipped.
The needle fails to catch the
needle thread loop on the double
chain looper, resulting in the stitch
skipping shown below.
Defectively interlaced loop
Needle thread
The needle thread extends
to the adjacent stitch.
11. Overlocking chain-off thread is bad.
Provided that no chain-off trouble oc-
curred when sewing operation was
done with materials set on the machine.
Case (1)
Double chain looper
Adjustment of looper
Thread tension
Stitch length
Needle guard
Double-chain stitch needle thread
guide.
Position of the throat plate
Feed dog
Adjustment of looper
Thread tension
Case (2)
The chain looper is too high and too close
to the throat plate, or has bad shape.
The return is not enough, causing the
needle to miss the loop.
The needle thread tension is too low.
The stitch length is as small as 1.5 mm
or less.
A needle guard is too high, and catches
needle thread loops.
The needle thread guide is installed too
high, and it fails to tense the thread.
The throat plate has been improperly
positioned longitudinally, and chain-off
thread gets in between the main feed dog
and throat plate, causing defective chain-off
thread.
The auxiliary feed dog has scratch.
The auxiliary feed dog is too high, and
interferes with chain-off thread. The auxiliary
feed dog is too low.
(Lower than the main feed dog by more
than 0.5 mm)
Adjustment of loopers for producing
chain-off thread without materials requires
higher accuracy.
The thread tension is too low.
The needle thread tension is too high,
causing damaged balance with other
thread tension.
Check and Corrective measures
Correct the height of the chain looper by
pushing it down until it cones into contact
with the stopper. Replace the chain looper
having a bad shape.
Refer to the related Standard Adjustment.
Slightly increase the needle thread tension.
Slightly increase the stitch length.
Adjustment of loopers for producing chain-off
thread without materials requires higher
accuracy than that with materials.
Refer to the related Standard Adjustment.
Refer to the related Standard Adjustment.
Correctly position the throat plate.
Repair or replace the auxiliary feed dog.
Refer to the pertinent Standard Adjustment.
Refer to the related Standard Adjustment.
Slightly increase the tension.
Check whether the needle thread take-up
guide or needle thread guide is positioned
too high with consequent excessive needle
hread tension. And if so, correct it.
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