JUKI LK-1900A Series Engineer's Manual page 101

Trouble
3. Stitch Skipping
4. Thread breakage
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Cause (1)
3-1) Too much clearance between
the needle and the inner hook.
3-2) Inadequate timing adjustment
for the needle and the inner hook.
3-3) Inadequate clearance between
the shuttle driver and the needle
3-4) Material to be sewn is not
properly stretched.
3-5) Needle is bent or blunt.
3-6) Loop of the needle thread
falls down.
4-1) Stratches on the inner hook
A
C
B
D
4-2) Thread enters into the shuttle.
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Cause (2)
4-A) Too much clearance between
the work clamp foot and
sewing object
6-A) Feed timing is too fast.
1-A) Scratches on section
A
(Contact of the inner hook with
the needle)
1-B) Scratches on section
B
(Scratches occur when the
needle is bent or broken.)
1-C)Scratches on section
C
(Needle scratches the inner hook
when removing the inner hook.)
1-D)Scratches on section
D
2-A) Position of the shuttle upper
spring is wrong.
2-B) Blade point section of the
A
shuttle is round.
A
2-C)Position of the shuttle is wrong.
2-D)Needle thread tension is too low.
Check and corrective measures
Adjust the clearance between needle and inner hook.
Adjust timing for the needle and the inner hook.
Adjust the clearance between needle and shuttle driver.
Adjust the work clamp foot height.
Remove the slackness of the sewing object.
Replace the needle.
Attach the needle with the long groove orienting slightly
to the right. (Approximately 20°)
Change the feed timing by the use of the memory switch.
After polishing the blade point of the inner hook with
oilstone, polish it with polishing powder. Properly adjust
the clearance between the needle and the inner hook.
After polishing the blade point of the inner hook, polish it
with polishing powder.
After polishing the blade point of the inner hook, polish it
with polishing powder.
After polishing the blade point of the inner hook, polish it
with polishing powder.
Properly adjust the position of the shuttle upper
spring.
Replace the inner hook.
Properly adjust the position od the shuttle.
Properly adjust the needle thread tension.