JUKI MF-7900 Series Engineer's Manual page 71

Adjustment procedures
2. Adjusting the height of the needle bar
(1) Loosen setscrew ❾ in the needle bar bracket and adjust the
height of the needle bar.
(2) After adjusting the height of the needle bar, adjust clearances
C provided between needles ❽ and needle holes H in the
throat plate to equal and fix the needle bar with setscrew ❾ .
* Refer to "4.-(10) Height of the needle".
3. Adjusting the needle guard
Standard position of the rear needle guard
(1) Lateral position of rear needle guard
It is the standard that the lateral position of rear needle guard
❶ is the position where the rear needle guard ❶ receives the
needle in the range of B.
(2) Position of the height of the rear needle guard
It is the standard that the clearance provided between crest line
A of rear needle guard ❶ and the top end of right needle is 1.5
to 2 mm when top end of the looper ❸ comes from the extreme
right position to the center of right needle.
(3) Pressing amount of the rear needle guard
It is the standard that when top end of the looper ❸ comes
from the extreme right position to the center of right needle, the
clearance provided between the right needle and top end of the
looper ❸ is 0 to 0.05 mm, when top end of the looper ❸ comes
to the center of middle needle, the clearance provided between
the middle needle and top end of the looper ❸ is 0 to 0.05 mm,
and the pressing amount of the top end of needle touches the
rear needle guard ❶ .
* For the details, refer to the standard adjustment procedure in
"4.-(12) Adjusting the needle guard".
4. Adjusting the front needle guard
(1) Height of the front needle guard
It is the standard position that the height of front needle guard
❷ is positioned higher by 3.3 ± 0.5 mm than rear needle guard
❶ .
(2) Clearance provided between the needle and the front needle
guard
It is the standard that the clearance provided between the nee-
dle and front needle guard ❷ is 0.2 to 0.5 mm.
* For the details, refer to the standard adjustment procedure in
"4.-(12) Adjusting the needle guard".
Results of Improper adjustment
◦ When the position of the height
of the needle bar is excessively
different, stitch skipping, needle
breakage, thread breakage, etc.
will be caused.
◦ When the adjustment value is
excessively different from the
specified value, needle breakage
or stitch skipping will be caused.
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