Adjustment To Prevent Triangular Stitch Skipping In The Case Of A Narrow Needle Throwing Width - JUKI MEB-3810N Series Instruction Manual

10-4. Adjustment to prevent triangular stitch skipping in the
case of a narrow needle throwing width
Spreader, left
Outer needle
Stitch skips when the
thread enters here
Needle thread
Inner needle
(lower dead point of inside needle)
A > B
(lower dead point of outside needle)
Throat plate
Looper thread
triangle (C)
Looper thread
Looper, left
A
Needle
B
Needle
❷
❶
❸
For sewing with the narrow needle throwing width of
2 mm or less, the outer needle enters the left side of
the looper thread triangle (C section) when the outer
needle comes down during sewing in the standard
adjustment state. This can cause stitch skipping.
In this case, carry out the following adjustment after
the completion of the adjustment described in
Timing between the needle and the looper" p. 79
and "10-3. (1) Adjusting the needle bar height" p.
82 completed.
1) Turn the hand pulley by hand when the looper
thread is hooked on the looper to lower the outer
needle.
2) Loosen setscrew ❶ in the looper driving shaft guide.
Move looper driving shaft guide ❷ upward to adjust
so that the outer needle enters the looper thread
triangle (C section) when the needle intersects the
looper, left; i.e., A is larger than B (A > B).
A guide of adjustment
When the looper timing is 2.7 mm:
Values A and B
A = Approx. 4 mm
B = Approx. 3 mm
3) Determine the position of looper driving shaft guide
❷ so that clearance d provided between the outer
needle and the looper thread is minimized. Then,
fix the looper driving shaft guide with setscrew ❶.
Take care not to damage or deform needle
thread trimming spring ❸.
Even when the outer needle enters the loop-
er thread triangle (C section) by turning the
hand pulley by hand, the needle sometimes
enters outside the C section resulting in
stitch skipping during sewing. If stitch skip-
ping occurs, adjust dimension d as small as
possible so that the outer thread enters C
section during sewing.
− 83 −
"10-2.