JUKI LH-4500C Series Instruction Manual page 184

Phenomenon
① Clearance between the needle and the
2. Stitch skipping
hook blade point is too great.
② Timing between the needle and the
hook is excessively advanced or
retarded.
③ Pressure of the presser foot is too low. ◦ Tighten the presser spring regulator.
④ When the needle thread slips out of the
rotary disc.
⑤ Improper type of needle is used.
⑥ Synthetic thread or thin thread is used. ◦ Wind the thread on the needle.
⑦ Stitch skipping occurs at the beginning
of sewing.
⑧ Stitch skips when sewing multilayered
parts of the material.
⑨ Stitch skipping occurs when the materi-
al thickness changes, i.e., from a two-
ply part to a multi-layered part and vice
versa.
① Bobbin thread does not pass through
3. Loose stitches
the forked end of the tension spring on
the bobbin case.
② Thread path has rough surface.
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.
⑦ The presser foot does not securely
press the multi-layered section of the
material.
⑧ Needle eyelet is too small for thickness
of thread, preventing smooth take-up
motion of the thread take-up lever.
⑨ With respect to tensing of thick
thread, neither needle thread tension
nor bobbin thread tension can be
increased, resulting in production of
isolated idling loops.
⑩ Isolated idling loops are produced
during the reverse feed stitching.
Cause
◦ Refer to
◦ Refer to
◦ Refer to
◦ Replace the needle with one which is thicker than
◦ Use the optional needle clamp wire.
◦ Run the sewing machine under the soft start mode
◦ Use the needle thread guide and precisely adjust
◦ Move the presser foot toward the operator.
◦ Thread the bobbin case correctly.
◦ Remove rough parts with a fine emery paper or
◦ Replace the bobbin or hook with a new one.
◦ Refer to
◦ Adjust the bobbin thread tension.
◦ Decrease the tension applied to the bobbin winder.
◦ Change presser foot with the hinging presser
◦ Retard the hook timing by 2 to 3 degrees.
◦ Use the needle thread take-up eyelet.
◦ Use the needle thread presser.
◦ Use the bobbin thread tension spring t0.3 (2261
◦ Retard the hook timing.
– 179 –
Corrective measures
"8-1. Needle-to-hook relation"
"8-1. Needle-to-hook relation"
"8-1. Needle-to-hook relation"
the current needle by one count.
by 2 to 3 stitches from the sewing start.
the hook timing.
At this time, be careful not to allow the presser foot
to come in contact with the needle.
buff it up.
"8-4. Adjusting the bobbin case
opening lever" p.110.
(B1524512FBE).
(The presser foot with large front and rear
elevation angles is pRefer to rable.)
2808).
p.105.
p.105.
p.105.