Troubles And Corrective Measures - JUKI LH-3500A series Instruction Manual

9. TROUBLES AND CORRECTIVE MEASURES

TROUBLES
. Thread breakage
(Thread s untwsted
or scraped.)
(Needle thread 2 to
3 cm s left on the
wrong sde of the
fabrc.)
(Bobbn thread
comes out of the
bobbn.)
2. Sttch skppng
CAUSES
1 There s a sharp edge or burr on
the thread path, needle pont, hook
blade pont or bobbn case restng
groove on the throat plate.
2 Needle thread tenson s too hgh.
3 Bobbn case openng lever
provdes an excessve clearance
at the bobbn case.
4 Hook blade pont hts the needle.
5 Hook s not lubrcated properly.
6 Needle thread tenson s too low.
7 Thread take-up sprng s too tght
and ts stroke s too small.
8 Needle-to-hook tmng s wrong.
9 Thread untwnes.
!0 Unform thread loops cannot be
formed when makng chan-off
thread.
!1 Bobbn s wound wth excessve
amount of thread. (In partcular,
filament thread)
1 Clearance between the needle and
the hook blade pont s too great.
2 Needle-to-hook relaton s wrong.
3 Pressng force of the presser foot
s not enough.
4 Needle bar heght s wrong.
5 Needles are a lttle too thn.
6 Synthetc thread or thn thread s
used.
7 Sttch skppng occurs at the
begnnng of sewng.
8 Sttch skps when sewng
multlayered parts of the materal.
9 Sttch skppng occurs when the
materal thckness changes, .e.,
from a two-ply part to a mult-
layered part and vce versa.
CORRECTIVE MEASURES
™ Remove sharp edge or burr using a fine
sandpaper. Polsh the surface of the
bobbn case restng groove on the throat
plate using a buffing wheel.
™ Adjust the needle thread tenson.
™ Reduce the clearance.
(Refer to
guide", p.
™ Refer to
p. 27.
™ Increase the amount of ol suppled to the
hook accordng to
amount of oil in the hook", p.
™ Adjust the needle thread tenson.
™ Reduce the tenson of the sprng and
ncrease the stroke.
™ Refer to
p. 27.
™ Wnd the thread on the
needle.
™ Use the thread gude equpped wth felt
pad.
™ Use the optonal needle clamp wre.
™ Wnd the bobbn wth thread by 80 % of ts
capacty.
™ Refer to
p. 27.
™ Refer to
p. 27.
™ Tghten the presser sprng regulator.
™ Refer to
p. 27.
™ Replace the needle by thcker ones.
™ Wnd the thread on the needle.
™ Use the optonal needle clamp wre.
™ Run the sewng machne under the soft
start mode by 2 to 3 sttches from the
sewng start.
™ Use the needle thread gude and precsely
adjust the hook tmng.
™ Move the presser foot toward the operator.
At ths tme, be careful not to allow the
presser foot to come n contact wth the
needle.
– 53 –
"6-5. Adjusting the inner hook
37.)
"4-17. Needle-to-hook relation",
"4-4. Adjusting the
9.
"4-17. Needle-to-hook relation",
"4-17. Needle-to-hook relation",
"4-17. Needle-to-hook relation",
"4-17. Needle-to-hook relation",