JUKI MO-6800S Series Engineer's Manual page 67

WARNING :
Turn OFF the power before starting the work so as to prevent accidents caused by abrupt start of the sewing machine.
Trouble
17. The looper thread bulges out
18. Looper thread bite
19. Knotting position is not correct.
Right side
Knots are
deflected to
the upper
looper side.
20. Uneven material feed
Cause (1)
17-1) Knife width 1-A)
17-2) Adjustment of the 2-A)
looper thread take-up
18-1) Knife width 1-A)
18-2) Adjustment of the 2-A)
looper thread take-up
19-1) Threading 1-A)
19-2) Adjustment of the 2-A)
looper thread take-up
2-B)
20-1) Presser foot pres- 1-A)
sure
20-2) Presser foot 2-A)
2-B)
20-3) Tilt of feed dogs 3-A)
20-4) Height of feed dogs 4-A)
20-5) Adjustment of differ- 5-A)
ential feed
Cause (2)
The knife width is too small for the over-
edging width.
The looper thread take-up draws out
excessive looper thread.
The knife width is too large for the over-
edging width.
The looper thread take-up draws out
insufficient amount of looper thread.
Re-threading after thread breakage,etc.
has been done erroneously.
The height of the looper thread take-up
(left) is not correct.
The upper looper thread guide (right) is
too short.
The presser foot pressure is too high.
The hinge is too stiff.
Scratches on or defective finish on the
presser foot sole produce friction be-
tween the presser foot and materials.
The front is too high.
A different in level exists between the
main feed dog and differential feed dog.
The differential feed has been improp-
erly adjusted.
Checking order and adjusting procedure
Use a knife having width suited to the overedging
width.
Decrease the radius of the looper thread take-up
(left). Raise the looper thread take-up (right).
Use a knife having width suited to the overedging
width.
Increase the radius of the looper thread take-up
(left). Lower the looper thread take-up (right).
Refer to the threading diagram.
Raise the looper thread take-up (left) to increase
the amount of upper looper thread, and the knot-
ting position moves toward the lower looper side.
Lengthen the upper looper thread guide (right).
Reduce the presser foot pressure except for the
uneven material feed due to packering.
Remove the stiffness provided no hinge play is
produced.
Buff the presser foot sole for good surface finish.
Make the front down. However, be sure to align
the differential feed dog with the main feed dog.
Eliminate the difference in level.
Provide differential feed suited to the material.