Brother LH4-B800E Service Manual page 105

4. Adjustment
4-13-8. Adjusting the upper thread scissors opening timing
Approx. 1—1.5 mm
Turn on the power and set the sewing machine to the home position. Then press the RESET key to lower the presser
foot.
1. Loosen the screw q, and then adjust the support plate r so that the back plate w and the cam e overlap by
approximately 1—1.5 mm.
If the amount of overlap is too small, the upper thread scissors will not open properly and the upper thread
scissors and the cutter may touch each other.
2. Loosen the screw t to adjust so that the clearance between the back plate w and the cam e is approximately 2
mm. Reduce this clearance if you would like the upper thread scissors to open more quickly.
3. Check that the distance (A) between the upper thread scissors y and the center of the needle u is 5.5—6 mm.
If the distance (A) is less than about 4.5 mm, the upper thread scissors y may touch the needle when they
*
open, which may result in needle breakages.
If the distance (A) is outside the range of 5.5--6 mm, loosen the screw i and move the dog o in the direction
of the arrow slightly. Then tighten the screw i, turn the power back on, set the sewing machine to the home
position nd then press the RESET key to check the adjustment.
4. Check the operation in test feed mode.
* Refer to the operating procedure given in "1-10. Upper thread trimmer mechanism".
4 - 18
o
i
w
e
Approx. 2 mm
y
(A) 5.5 - 6 mm
u
Approx. 2 mm
q
r
w
LH4-B800E
t
e
w
Approx. 1—1.5 mm
Approx. 1—1.5 mm
e
q
t r