JUKI LK-1900AN Engineer's Manual page 25

Adjustment procedures
If the main shaft eccentric cam 8 is not fixed, this adjustment
should be carried out after defining its position and fixing it.
1. Loosen the two set screws 7 of the crank balancer 6 .
2. Using the four set screws 2 , remove the crank rod cover 1 .
3. Turn the main shaft in the direction of forward rotation A so
that the needle bar 3 lowers and the clearance between the
needle bar connecting 4 and the needle bar bushing, lower 5
is 5.7 mm (LK-1903AN: 4.6 mm).
4. In the state that the two set screws 7 of the crank balancer
6 assume the horizontal condition and they are moved in the
direction of the arrow mark B , keep the close contact with the
main shaft eccentric cam 8 and tighten the two set screws 7 .
When tightening these two set screws 7 , the screws should be
tightened reciprocally.
Adjustment procedures
1. Lower shaft backlash
1) Loosen the two set screws 1 .
2) Turn the lower shaft rear metal 2 in the direction of the ar-
row and adjust the backlash, keeping the metal to contact
closely with Face A.
Size of backlash is 0.1 mm at the tip of the driver 5 . The
shaft is required to rotate smoothly.
3) Tighten the two set screws 1 .
(Caution) When eliminate the backlash, the direction of rota-
tion should always be kept in the direction of the
arrow.
2. Lower shaft connection/disconnection
1) Loosen the two set screws 7 .
2) The lower shaft 6 can be taken out if it is pulled in the
direction C of the arrow.
3) When mounting the lower shaft 6 , insert it in the lower
shaft rear metal 2 and the lower shaft gear 3 . Apply one
of the set screws 7 to the flat section 8 of the lower shaft
6 and tighten it approximately in the center. Tighten the
remaining set screw 7 .
* Connection and disconnection of the lower shaft 6 become
easy if the above-mentioned backlash has been relieved in
advance. In this case, backlash adjustment must be done after
the lower shaft 6 has been installed.
Results of Improper adjustment
If the angle for fixing the crank
o
balancer 6 is inadequate, vibra-
tion of sewing machine opera-
tion will be intensified.
If the sewing machine is used
o
for a long time while the fix-
ing position is inadequate, the
operational life of the main shaft
bearing may be shortened.
If the crank balancer 6 is not
o
moved in the direction of the ar-
row mark B , there may be inter-
ference with the sewing machine
frame.
Results of Improper adjustment
If the backlash is excessive, the
o
hook noise will be increased.
If backlash is too small, the
o
lower shaft gear 3 or the oscil-
lator 4 will give rise to frictional
wear. In addition, this can be a
cause of crank rod lock-up.
If the front or rear position of
o
the lower shaft rear metal 2 is
displaced at the time of backlash
adjustment, this can also be a
cause of the lock-up of oscillator
4 or the crank rod.
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