JUKI MO-6000S series Engineer's Manual page 81

Trouble
2. Looper thread breakage
3. Needle breakage
Case (1)
Thread path
Adjustment of the looper thread take-up
Thread tension
Thread
Position of the thread guides
Double chain looper avoid (only for double chain
stitch)
Needle heat
Needle entry
Upper looper position
Contact with the looper
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Case(2)
Scratches, burrs, rust, etc, on the paw of the throat plate,
stitch tongue, looper, looper thread take-up, thread
guide, or tension discs causes friction.
The looper thread take-up or thread guide has been
improperly positioned, causing excessive thread
tension.
The looper thread tension is too high.
The thread is weak because of its poor quality.
The upper looper thread guide is too high, and the thread
taking balance is disturbed, resulting in the thread
breakage.
The double chain looper strikes the needle at the back,
causing the thread breakage.
The needle gets hot, and the looper thread breaks when
it comes in contact with the hot needle at the time of
needle stop.
The needle entry has not been correctly adjusted, and
the needle strikes the throat plate or presser foot.
The upper looper juts out too much or it is too low.
The needle strikes the looper, resulting in needle
breakage.
Check and Corrective measures
Remove such scratches, burrs, etc. and carry out thread
path finishing. Replace loopers or other components which
have been deformed, causing thread breakage.
Refer to the pertinent Standard Adjustment.
Reduce the tension while checking the tension balance
other looper thread.
Replace the thread by one with good quality.
Refer to the pertinent Standard Adjustment.
Correct the longitudinal motion of the double chain looper
so as not to cause the looper to strike the needle.
Refer to the clause relating to the needle heat causing
needle thread breakage.
Correct the needle entry.
Refer to the related Standard Adjustment.
Re-position the looper so that it does not come in contact
with the needle. Adjust the longitudinal motion of the
double chain looper for the contact of its back with the
needle.
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