Problems With Sewing And Corrective Measures - JUKI LG-158 Instruction Manual

26. PROBLEMS WITH SEWING AND CORRECTIVE MEASURES

Problems
1. Needle thread
breakage.
a. Needle thread
ravels and wears
out.
b. Thread breaks at
step-sewing part.
c. Due to inferior
quality of the needle
thread.
d. Needle thread
breaks at the start
of sewing or slips
out.
e. Bobbin thread
breaks.
2. Skip-stitching
Causes
① Bruise on thread path, needle point,
blade point of sewing hook and groove
of bobbin case holder rotation stopper
on backside of throat plate.
② Tension of needle thread is too strong.
③ Hardly no clearance between bobbin
case opening lever and bobbin case
holder.
④ Needle and the sewing hook are hitting
each' other.
⑤ The oil supply to the sewing hook is
insuffi cient.
⑥ Needle is too fi ne against the using
thread.
① Lifting amount of presser foot and
walking foot is too small.
① When the twist has fl ows and knots or
constrictions are formed.
② When old threads are used sometimes
they break easily with slight pressure.
① Position of the thread take-up lever is
not at the upper dead point.
① Bobbin is defective and rotation is not
smooth.
② When thread hards get between the
bobbin and the bobbin case opener.
① Clearance between the needle and
blade point of hook is too wide.
② Timing of sewing hook and needle is
either too fast or too slow.
③ Presser foot is "fl oating". (When
pressing pressure is too weak.)
④ Installed angle of the needle is bad.
○ Polish off the bruise of blade point of hook with
a fi ne mesh paper fi le. Finish the groove part of
throat plate by buffi ng.
○ Refer to the chapter on "8. THREAD TENSION".
○ Loosen the set screw of the bobbin case opening
lever and make the clearance between bobbin
case opening lever and bobbin case holder to 0.4
mm(1/64")
(Refer to the chapter on "13. ADJUSTING THE
BOBBIN CASE OPENING LEVER".)
○ Tap the hook driving shaft saddle lightly and
adjust the clearance between the needle and
the blade point of the sewing hook. (Refer to the
chapter on "11. ADJUSTING THE WALKING
FOOT AND PRESSER FOOT".)
○ Adjust the oiling amount to the sewing hook.
○ Refer to the chapter on "STANDARD STITCHING
SPECIFICATIONS".
○ Increase the lifting amount of presser foot and
walking foot. (Refer to the chapter on "20.
ADJUSTING THE LIFTING AMOUNT OF THE
PRESSER FOOT AND THE WALKING FOOT".)
○ Exchange the thread.
○ Exchange with new thread.
○ Bring the thread take-up lever to the upper dead
point and start sewing.
○ Exchange the bobbin with a new one.
○ Take out the bobbin and after removing the
thread hards, reset the bobbin.
○ Adjust the clearance between the needle and the
blade point of sewing hook. (Refer to the chapter
on "11. ADJUSTING THE WALKING FOOT
AND PRESSER FOOT".)
○ Adjust the timing of needle and sewing hook.
(Refer to the chapter on "11. ADJUSTING THE
WALKING FOOT AND PRESSER FOOT".)
○ Tighten the pressure regulating thumb screw.
○ Refer to the chapter on "4. HOW TO INSTALL
THE NEEDLE".
– 14 –
Corrective measures