JUKI MO-6000S series Engineer's Manual page 86

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 occurred
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 thread tension. And if so, correct it.
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