With Regard To Lubrication - JUKI DNU-1541 Engineer's Manual

Troubles
Loose stitches
(Balloon stitches or isolated
idling loop)
Loose stitches
(Needle thread rises.)
Irregular stitches

(2) With regard to lubrication

Troubles
Oil does not enter the hook.
Causes
Bobbin thread is not
passed to the fork end of
bobbin case tension spring.
Thread paths have been
poorly finished.
Bobbin fails to move
smoothly.
Bobbin case is improperly
engaged.
Thread is not well tightened
in the reverse feed.
Height of the feed dog is too
high.
Feed timing is excessively
advanced.
Hard-to-slip thread is used.
Needle thread has not
been fully pulled up.
Stroke of the thread take-
up spring is improper.
Thread paths have been
poorly finished.
Bobbin thread tension is too
low.
Bobbin has been wound
too tight.
Pressure of the idle
prevention spring is too
high.
Causes
Oil amount in the oil tank is
too small.
Oil amount adjusting screw
is improperly adjusted.
Lead groove in the hook
shaft is clogged with dust.
Checking
Check the bobbin thread
route.
Check the finish of the
respective thread paths.
Check the change of
bobbin thread tension.
Compare the height with
the standard value.
Check the stroke of the
thread take-up spring.
Check the finish of the
respective thread paths.
Check the state of bobbin
winding.
Check the idling amount of
the bobbin.
Checking
Check the oil level.
50
Corrective measures
Correctly pass thread to the bobbin
case.
Finish using a fine emery paper or
buff.
Replace the bobbin or the hook.
Replace the bobbin case or the hook.
Use the optional walking foot and
presser foot.
Refer to "(4) Height of the feed dog".
Lower the height by 0.2 mm than the
standard value.
Retard the feed timing.
Use silicone oil.
(Refer to "(4) Others *").
Increase the needle thread tension.
Use the optional walking foot.
(Top-devided type)
Adjust the thread take-up spring to
move to approximately 1 mm from
the initial position when hook draws
thread maximumly.
Finish with a fine emery paper or buff.
Increase the tension of the bobbin
thread.
Decrease the tension applied to the
bobbin winder.
Decrease the pressure of the idle
prevention spring.
Corrective measures
Refer to "(15) Lubrication".
Draw out the hook shaft and wash
the lead groove.