– 167 –
Troubles Causes Corrective measures
4. Thread slips off
the needle eyelet
simultaneously with
thread trimming.
Thread tension given by the tension
controller No. 1 is too high.
Thread take-up spring stroke is too large.
○
Decrease the thread tension given by the
tension controller No. 1.
○
Decrease the stroke.
5. Thread slips off the
needle eyelet at the
start of sewing.
Thread tension given by the tension
controller No. 1 is too high.
Clamp spring has improper shape.
Bobbin thread tension is too low.
Thread take-up spring stroke is too large.
○
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.
○
Decrease the stroke.
6. Faulty intertwining of
the needle thread and
bobbin thread at the
beginning of sewing.
The bobbin thread clamp pressure is
high.
○
Decrease the bobbin thread clamp pressure.
Refer to
"8-5. Adjusting the position of
counter knife, knife pressure and clamp
pressure" p.110
.
○
Hold the needle thread on the material.
7. Thread is not cut
sharply.
The blades of moving knife and counter
knife have been improperly adjusted.
The knives have blunt blades.
Bobbin thread tension is too low.
○
Refer to
"8-5. Adjusting the position of
counter knife, knife pressure and clamp
pressure" p.110
.
○
Replace the moving knife and counter knife
with new ones, or correct the current ones.
○
Increase the bobbin thread tension.
8. Thread remains uncut
after thread trimming.
(Bobbin thread
trimming failure
when stitch length is
comparatively short.)
Initial position of the moving knife has
been improperly adjusted.
Bobbin thread tension is too low.
○
Refer to
"8-5. Adjusting the position of
counter knife, knife pressure and clamp
pressure" p.110
.
○
Increase the bobbin thread tension.
9. Thread breaks at the
start of sewing after
thread trimming.
The needle thread is caught in the hook.
○
Shorten the length of thread remaining on the
needle after thread trimming.
Refer to
"4-1. Thread tension" p.33
.
10. When a heave-weight
material is sewn, the
material warps.
The feed amount of the top feed is
inadequate.
○
Decrease the feed dog height and reduce
the feed amount of the bottom feed. (Refer
to the Engineer's Manual for the adjustment
procedure.)
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