JUKI MEB-3200 Engineer's Manual page 49

Adjustment Procedures
3) Adjusting the knife pressure
1. Loosen nut !3 on the bottom face of the presser plate.
2. Slightly tighten fulcrum screw ! 0 to the full and return it by one
to half rotation. Press fulcrum screw !0 so that it cannot be
turned and fix it with nut !3 in the rear.
Check the knife pressure by test trimming of rather thick thread
by hand. Especially check the pressure by test trimming at the
top end and the root of the blade section.
4. If the knife is dull, decrease the amount of return of fulcrum
screw !0 . At this time, tighten fulcrum screw !0 within the range
where the return motion of upper knife 5 and lower knife 1
does not become bad. Then fix it with nut !3 .
(Caution) 1. In case thread trimming failure occurs even
when fulcrum screw !0 is tightened until the
return motion of upper knife 5 and lower knife
1 becomes bad, replace the knife or resharpen
the blade section.
2. When setscrew ! 1 is removed and the knife is
removed together with the knife unit in case of
replacement of the presser set or the like, the
knife pressure does not change. It is not
necessary to adjust the pressure.
3. Apply a small quantity of grease to section B of lower
knife 1 where comes in contact with upper knife
lower cover !4 for a long period of time.
4) Adjusting the position of the thread haul plate
1. Loosen two setscrews ! 6 and move thread haul plate ! 7 to
adjust the position.
1) Normally, move thread haul plate !7 in the direction of arrow
mark D to adjust the position to such an extent that it hides
the blade top of upper knife 5. Then secure an enough
clearance C.
2) When the sewing length is short and the looper thread on
the side of sewing start runs away from the knife at the time
of thread trimming, adjust the position slightly to the reverse
direction from D.
2. For the final confirmation, expel the air and operate the plate
by hand, or actually turn ON looper thread trimming cylinder ! 4
with the test mode 2 or the like, and check that there is no
interference.
When trimming the looper thread, presser goes up and cloth
open mechanism is open.
(Caution) When adjusting the position where the cloth open
mechanism is open, be sure to check the position of thread
haul plate !7 . Position A where the cloth open mechanism
is open requires 1.0 mm or more. If it is less than 1.0 mm,
clearance C may not be secured. (Refer to "(9) Adjusting
the cloth open".)
Results of Improper Adjustment
When the fulcrum screw is excessively
tightened :
™ Return of the knife becomes bad
and needle may interfere with the
knife.
™ Similarly, error is detected due to
the defective return of the looper
thread trimming cylinder and the
sewing machine may stop.
™ Breakage/worn-out of the blade
may be caused since the knife
pressure is excessively high and the
service life of the blade will be
deteriorated.
When the fulcrum screw is insufficiently
tightened :
™ A proper knife pressure cannot be
obtained and thread trimming failure
will occur.
When the thread haul plate excessively
comes out in the reverse direction from
the arrow mark direction of D :
™ The presser steps on the plate
when the presser comes down and
deformation may be caused.
™ Similarly, the presser steps on the
plate, and the upper knife and upper
knife lower cover come down. As a
result, interference with the throat
plate will be caused at the time of
feed.
™ The plate interferes with the holding
plate and presser foot when the
knife works. As a result, breakage
or defective motion will be caused.
When the thread haul plate is
excessively with drawn in the arrow
mark direction of D :
™ The looper thread at the sewing
start runs away from the blade
section of knife at the time of thread
trimming. As a result, thread
trimming failure will be caused.
When the thread haul plate is
excessively put back to this side
(cylinder side) :
™ The looper thread at the sewing
start runs away from the blade
section of knife at the time of thread
trimming. As a result, thread
trimming failure will be caused.
™ The blade section of upper knife is
exposed and material or seams will
be cut at the time of thread trimming.
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