27. Troubles In Sewing And Corrective Measures - JUKI LU-1500N Serie Manual De Instrucciones

27. TROUBLES IN SEWING AND CORRECTIVE MEASURES

Troubles
1. Thread breakage
(Thread frays or is worn out.)
(Needle thread trails 2 to 3
cm from the wrong side of the
fabric.)
2. Stitch skipping
3. Loose stitches
4. Thread slips off the needle
eyelet simultaneously with
thread trimming.
5. Thread slips off the needle
eyelet at the start of sewing.
6. Thread is not cut sharply.
7. Thread remains uncut after
thread trimming.
( B o b b i n t h r e a d t r i m m i n g
failure when stitch length is
comparatively short.)
8. Thread breaks at the start of
sewing after thread trimming.
Causes
1 Thread path, needle point, hook blade point or
bobbin case resting groove on the throat plate
has sharp edges or burrs.
2 Needle thread tension is too high.
3 Bobbin case opening lever provides an exces-
sive clearance at the bobbin case.
4 Needle comes in contact with the blade point of
hook.
5 Amount of oil in the hook is too small.
6 Needle thread tension is too low.
7 Thread take-up spring works excessively or the
stroke of the spring is too small.
8 Timing between the needle and the hook is ex-
cessively advanced or retarded.
1 Timing between the needle and the hook is ex-
cessively advanced or retarded.
2 Pressure of the presser foot is too low.
3 The clearance provided between the top end of
the needle eyelet and the blade point of hook is
not correct.
4 Hook needle guard is not functional.
5 Improper type of needle is used.
1 Bobbin thread does not pass through the ten-
sion spring of the inner hook.
2 Thread path has been poorly fi nished.
3 Bobbin fails to move smoothly.
4 Bobbin case opening lever provides too much
clearance at the bobbin.
5 Bobbin thread tension is too low.
6 Bobbin has been wound too tightly.
1 Thread tension given by the tension controller
No. 1 is too high.
1 Thread tension given by the tension controller
No. 1 is too high.
2 Clamp spring has improper shape.
3 Bobbin thread tension is too low.
1 The blades of moving knife and counter knife
have been improperly adjusted.
2 The knives have blunt blades.
3 Bobbin thread tension is too low.
1 Initial position of the moving knife has been
improperly adjusted.
2 Bobbin thread tension is too low.
1 The needle thread is caught in the hook.
– 55 –
Corrective measures
™ Remove the sharp edges or burrs on the
blade point of hook using a fi ne emery pa-
per. Buff up the bobbin case resting groove
on the throat plate.
™ Decrease the needle thread tension.
™ Decrease the clearance provided between
the bobbin case opening lever and the bob-
bin.
Refer to "21. ADJUSTING THE BOBBIN
CASE OPENING LEVER".
™ Refer to "19. NEEDLE-TO-HOOK RELA-
TION".
™ Adjust the amount of oil in the hook prop-
erly.
Refer to "7. LUBRICATION".
™ Increase the needle thread tension.
™ Decrease the tension of the spring and in-
crease the stroke of the spring.
™ Refer to "19. NEEDLE-TO-HOOK RELA-
TION".
™ Refer to "19. NEEDLE-TO-HOOK RELA-
TION".
™ Tighten the presser spring regulator.
™ Refer to "19. NEEDLE-TO-HOOK RELA-
TION".
™ Refer to "20. ADJUSTING THE HOOK
NEEDLE GUARD".
™ Replace the needle with one which is thicker
than the current needle by one count.
™ Thread the bobbin thread correctly.
™ Remove rough parts with a fi ne emery pa-
per or buff it up.
™ Replace the bobbin or hook with a new one.
™ Refer to "21. ADJUSTING THE BOBBIN
CASE OPENING LEVER".
™ Increase the bobbin thread tension.
™ Decrease the tension applied to the bobbin
winder.
™ Decrease the thread tension given by the
tension controller No. 1.
™ Decrease the thread tension given by the
tension controller No. 1.
™ Replace the clamp spring with a new one
or correct the current one.
™ Increase the bobbin thread tension.
™ Refer to "22. POSITION OF THE COUN-
TER KNIFE AND ADJUSTMENT OF THE
KNIFE PRESSURE".
™ Replace the moving knife and counter knife
with new ones, or correct the current ones.
™ Increase the bobbin thread tension.
™ Refer to the Engineer's Manual.
™ Increase the bobbin thread tension.
™ Shorten the length of thread remaining on
the needle after thread trimming.
Refer to "15. THREAD TENSION".