JUKI MO-6700D Series Manual page 59

Trouble
12. Problems with double chain stitch
chain-off thread.
Case (1)
Adjustment of loopers
Needle Guard
Position of the throat plate
Throat plate
Presser foot
Main feed dog
Double hooking
Thread tension
Case (2)
Adjustment of the loopers for producing
chain-off thread without materials requires
higher accuracy.
The needle guard (C) is too high,
damaging loops.
The needle comes into contact with the front
edge of the needle hole in the throat plate.
The lateral position of the throat plate with
respect to the feed dogs is wrong, causing
chain-off to drop in.
A dent exists on the flat part between the
rear edge of the needle hole and feed dog
groove.
Dent
The rear pressure foot is indented and not
flush with the presser foot sole, so that it
cannot hold chain-off thread.
The leading edge of the main feed dog is
too sharp and cuts chain-off thread.
The needle thread is not drawn up fully
because of the insufficient return of the
double chain looper or wrong threading.
If the feed pitch is too small, the cam
timing will be advanced.
The needle is bend or chain-odd thread
runs back due to excessive needle thread
tension.
Both the needle thread and looper thread
tension are too low.
Check and Corrective measures
Refer to the related Standard Adjustment.
Refer to the related Standard Adjustment.
Correctly position the throat plate.
Repair or replace the throat plate, since such
dent causes chain-off thread to slip out.
Replace it, or correct it to make it flush with
the presser foot sole.
Buff the leading edge of the main feed dog.
Refer to the related Standard Adjustment for
the return of the double chain looper. See the
threading diagram for correct threading.
Retard the cam timing.
Reduce the needle thread tension.
Slightly increase the both tensions.
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