Troubles And Corrective Measures - JUKI MO-6700D Series Manual

6. TROUBLES AND CORRECTIVE MEASURES

Trouble
1. Needle thread breakage
Case (1)
Threading
Thread path
Needle guard
Needle
Needle heat
Thread
Thread tension
Contact
Double thread hooking
(only for double chain stitch)
Defective double chain-off thread
(only for double chain stitch)
Case (2)
The thread is entangled with the thread
guide, or the machine head has been
incorrectly threaded.
Scratches, burrs or rust on the pawls
or needle holes of the throat plate,
stitch tongue, lower looper, double chain
looper, needle thread take-up, needle
thread presser spring, thread guide,
or tension discs causes friction.
The needle hits the needle guard intensely,
and sharp edges are produced on them,
causing thread breakage.
The needle is too thin for the thread.
The needle gets very hot, depending on
the type of materials, number of plies and
sewing speed, and causes the thread to
burn and break.
The thread is weak because of its poor quality.
The thread tension is too high.
The double chain looper or lower looper
has been improperly positioned and strikes
the feed dog or throat plate.
Poor drawing up of the needle thread
causes the looper to catch it again.
Refer to the clause referring to defective
double chain-off thread.
Check and Corrective measures
Refer to the threading diagram.
(Refer to the Instruction Manual)
Remove such scratches, burrs, etc. and
perform thread path finishing. Replace major
components such as looper, which have
been deformed, causing thread breakage.
Replace the needle and needle guard if
they have worn,
Replace the needle by a proper one.
Use a thinner needle. Reduce the sewing
speed. Use the needle cooler. Use an S-point
needle or needle for synthetic thread.
Replace the thread by one with good quality.
Reduce the thread tension. Check whether the
needle thread take-up guide and needle thread
guide are positioned too high, causing such
excessive thread tension.
Properly position the double chain looper or
lower looper.
Increase the needle thread tension. Properly
position the thread cam. Properly position the
double chainstitch thread guide.
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