JUKI DDL-9000C-S Series Engineer's Manual page 183

Trouble
From the previous page
3. "Balloon" stitches (loose stitches
and looping)
Thread knots are formed on ei-
ther side of material as a random
thread loop.
To the next page
Cause (1)
2-2) Pressing is inappropriate.
2-3) The sewing speed is too high.
3-1) The thread tension is too low.
3-2) The thread take-up spring is
inappropriately adjusted.
Cause (2)
2-A) The pressure is too high.
2-B) The finish of the backside of the
presser is rough.
2-C) The presser is made from Non-
smooth material.
2-A) The stroke of the thread take-
up spring is too short.
2-B) The tension is too low.
2-C) The shape of the thread take-
up spring is inappropriate.
2-D) The thread take-up spring ten-
sion is insufficient.
The following capability is insuf-
ficient at high speeds.
Check and corrective measures
Minimize the pressure. For some materials,
sewing with the presser slightly floated with the
adjustable screw of the minute presser lifter is
effective.
Buff the sole.
Use a fluorocarbon resin presser or a special
processed presser.
Reduce the sewing speed.
Increase the 2nd thread tension.
The thread take-up spring with too short stroke
cannot sufficiently take up the loosened thread
resulting in a higher possibility of balloon
stitches or thread breakage. The thread take-
up spring with too low tension cannot function
well at high speeds or sufficiently take up the
thread resulting in a higher possibility of bal-
loon stitches or thread breakage.
The thread take-up spring with too low tension
cannot function well at high speeds or sufficient-
ly take up the thread resulting in a higher possi-
bility of balloon stitches or thread breakage.
Thread slack may cause catching thread when the
tip of the thread take-up spring is open. If the open
level is too wide, use your finger to close the tip.
When #60 or thicker thread is used, the thread
take-up spring used in the A type is too weak
to exert its effect due to insufficient tension of
the spring at the end of the operation. In such
a case, use a standard type thread take-up
spring (or thread tension).