JUKI MH-380 Instruction Manual page 55

140331
Troubles
3. Inadequate tight-
ness of stitches
Causes
2 An independent seam is skipped on the
looper thread.
Needle
This trouble is caused when the needle
failed ·to come down through a trian-
gular loop formed by the looper thread.
3 Seam is skipped on the needle thread
due to insuffi cient interlooping.
Needle
Looper
This trouble is caused when the needle
thread is inclined extremely to the left.
If it is caused in the use of a chemical
fi ber thread.
If it is caused in the use of a synthetic
fi ber thread.
1 Needle thread tension is too low.
2 Looper thread tension is too high.
3 Looper thread take-up does not supply
a suffi cient length of thread.
4 Thread is too thick for the needle size.
5 Set position of the frame thread eyelet
is not suitable.
6 Position of the thread take-up lever is
not suitable.
7 Throat plate does not fi t.
™ Verify the looper motion.
Verify the clearance between the looper and
the needle.
Refer to "17. NEEDLE-TO-LOOPER RELA-
TION".
™ Check the timing of the looper thread take-up.
Refer to "19. POSITIONING THE LOOPER
Looper
THREAD TAKE-UP".
™ Increase the looper thread tension slightly.
Refer to "8. THREAD TENSION".
™ Verify the thread is correctly passed through.
Refer to "6. THREADING THE MACHINE
HEAD" and "7. THREADING THE LOOP-
ERS".
™ Verify the looper motion.
Verify the clearance between the looper and
the needle.
Refer to "17. NEEDLE-TO-LOOPER RELA-
TION".
™ Reduce the sewing speed.
™ Apply silicon oil lubricant.
Refer to "11. ATTACHING THE NEEDLE".
™ Use a needle for chemical fi ber threads.
™ Reduce the sewing speed,.
™ Apply silicon oil lubricant.
Refer to "11. ATTACHING THE NEEDLE".
™ Tighten the needle thread tension nut.
Refer to "8. THREAD TENSION".
™ Loosen the looper thread tension nut.
Refer to "8. THREAD TENSION".
™ Change the threading order in the looper thread
guide.
Refer to "19. POSITIONING THE LOOPER
THREAD TAKE-UP".
™ Try to use a different needle.
Refer to "11. ATTACHING THE NEEDLE".
™ Try to lower the position.
Refer to "21. POSITION OF THE FRAME
THREAD EYELET".
™ Try to push it up.
Refer to "20. POSITION OF THE THREAD
TAKE-UP LEVER".
™ Replace it with other throat plate which has
larger needle hole.
– 35 –
Corrective measures