Brother T-8421D Instruction Manual page 92

If the needle bar lift amount is too large
• It will cause poor tightening of the right thread.
• Both the left and right seams will become uneven, and skipped stitches or thread breakages will occur.
• Upper thread trimming errors may occur, or the upper thread may be cut too short. (T-8422D/T-8452D/
T-8722D/T-8752D)
• The upper thread trailing length after thread trimming will be too long. (T-8422D/T-8452D/T-8722D/T-8752D)
If the needle bar lift amount is too small
• Skipped stitches and thread breakages will occur.
• The upper thread trailing length after thread trimming will be too short. (T-8422D/T-8452D/T-8722D/
T-8752D)
8
Loosen the screws (10), and then remove rotary
hook base cover FL (11) and FR (12).
The screws (10) are designed so that they cannot
be removed from the rotary hook base cover FL
(11) and FR (12) to prevent them from being lost.
9
Loosen the set screws (13) (three each at left and
right).
However, be careful not to loosen them too much,
otherwise the set screws (13) will touch the inside
surface of the rotary hook base and the pinion gear
(14) will not be able to turn. Loosen the set screws
by the minimum amount which will still allow the
rotary hook to move freely.
10
Turn the rotary hook by hand to align the rotary
hook tip (15) with the middle of the needle.
Do not turn the machine pulley at this time.
11
Tighten the set screw (13).
Tighten the three set screws (13) a little bit at a
time in order so that the pinion gear (14) does not
become tilted.
12
Remove the tape that is securing the machine pulley.
13
Use an oil-based marker pen to color in the hollow
of the needle.
14
With the needle raised, turn the machine pulley
forward while pushing the needle against the rotary
hook tip (15) with your finger to make a mark from
the rotary hook tip (15) in the hollow of the needle.
15
Check that the distance (C) from the intersection
between the mark from the rotary hook tip (15) and
the center line of the needle to the top edge of the
needle hole is 1 to 1.5 mm.
<T-8421D/T-8422D/T-8722D>
• If the distance is not 1 to 1.5 mm, loosen the screw (5) again and adjust the height of the needle bar.
79