JUKI LK-1900AN, Engineer'S Manual

Page: 25 / 140

– 13 –
Adjustment procedures Results of Improper adjustment
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.
o
If the angle for fixing the crank
balancer
6
is inadequate, vibra-
tion of sewing machine opera-
tion will be intensified.
o
If the sewing machine is used
for a long time while the fix -
ing position is inadequate, the
operational life of the main shaft
bearing may be shortened.
o
If the crank balancer
6
is not
moved in the direction of the ar-
row mark
B
, there may be inter-
ference with the sewing machine
frame.
Adjustment procedures Results of Improper adjustment
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.
o
If the backlash is excessive, the
hook noise will be increased.
o
If backlash is too small, the
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.
o
If the front or rear position of
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.