Troubles And Corrective Measures - JUKI LBH-1790A Series Instruction Manual

IX. TROUBLES AND CORRECTIVE MEASURES
Troubles
1. Needle thread break- 1. Thread tension at parallel section is too high.
age
2. Pressure or stroke of thread take-up spring is
3. There is a burr or scratch on the blade point
4. Hook timing is not proper.
5. There is a scratch on the thread path.
6. Attaching needle is wrong.
7. Needle is too thin.
8. Needle tip is damaged.
9. Thread breaks when it is bent.
2. Needle thread slips off. 1. Needle thread trimmer opens too early.
2. Whip stitching is not formed at the start of
3. Threading needle thread is wrong.
4. Speed at the start of sewing is too fast.
3. Wobbling at parallel 1. Thread tension at parallel section is too low.
section
2. Bobbin thread tension is too high.
3. Pre-tension is too low.
4. Wobbling at the start 1. Thread tension at parallel section is too low.
of sewing
2. Position of needle thread trimmer is too high.
3. Stroke of thread take-up spring is too large.
5. Needle thread appears 1. Bar-tacking thread tension is too low.
on the wrong side of 2. Bobbin thread tension is too high.
material at bar-tacking
section in dumpling 3. Number of stitches of radial shape is too
condition.
4. Tension at the end of sewing is too low.
6. Stitches float. 1. Bobbin thread tension is too low.
2. Bobbin thread comes off bobbin case.
7. Stitch skipping 1. Button hole is small in terms of the size of
2. Material flops because of light-weight.
3. Attaching needle is wrong.
4. Needle is bent.
5. There is a burr or scratch on the blade point
8. Thread frays. 1. Number of stitches of tie stitching is too small.
2. Width of tie stitching is too wide.
9. Length of needle 1. Width of tie stitching is too narrow.
thread remaining at
the end of sewing is 2. Tension of tie stitching is too low.
too long.
Causes
too large.
of hook.
sewing.(Tension at the start of sewing is too
high.)
many.
presser.
of hook.
Corrective measures
○ Decrease the thread tension at parallel
section.
○ Decrease the tension of thread take-up
spring or decrease its stroke.
○ Buff the blade point of hook. Or, replace
the hook.
○ Adjust again the hook timing with timing
gauge.
○ Polish the thread path with sand paper
and buff it.
○ Adjust again the direction, height, etc.
○ Replace the needle with a thicker one.
○ Replace the needle.
○ Do not pass the thread through the thread
guide pin.
○ Delay the opening timing of the needle
thread trimmer.
○ Decrease tension at the start of sewing.
○ Thread properly again.
○ Set the soft-start function.
○ Increase the thread tension at parallel sec-
tion.
○ Decresase bobbin thread tension.
(Purl stitching : 0.05 to 0.1N )
○ Increase pre-tension.
○ Increase the thread tension at parallel sec-
tion.
○ Lower the needle thread trimmer to such
an extent that it does not come in contact
with the presser.
○ Decrease the stroke of thread take-up
spring.
○ Increase the bar-tacking thread tension.
○ Decresase the bobbin thread tension.
(0.05 to 0.1N )
○ Decrease the number of stitches.
○ Increase tension at the end of sewing.
○ Increase the bobbin thread tension.
○ Perform proper threading the bobbin case.
○ Take care that the winding amount of bob-
bin thread is not excessive.
○ Replace the presser with a smaller one.
○ Delay the hook-to-needle timing.
(Lower the needle bar by 0.5 mm.)
○ Adjust again the direction, height, etc.
○ Replace the needle.
○ Buff the blade top of hook. Or, replace the
hook.
○ Increase the number of stitches of tie
stitching at the end of sewing.
○ Narrow the width of tie stitching at the end
of sewing.
○ Widen the width of tie stitching at the end
of sewing.
○ Increase tension at the end of sewing.
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