Clearance Between Needle And Rotary Hook - Brother b831 Service Manual

[D NEEDLE AND ROTARY HOOK TIMING ADJUSTMENT
1. Clearance between needle and rotary hook point
Needle
Rotarv hook point
Should touch lightly
Needle guard o
0.05~0.1 mm
1 k
f 1
1P
r
0
sL
qI
(1) Loosen screws (a). ® and ©, and adjust the clearance between the needle and the rotary hook point to somewhere
between 0.05 and 0.1 mm by moving rotary hook O to right or left.
(2) After adjusting the clearance between the needle and the rotary hook point, adjust the needle guard so thatthe needle
and the needle guard lightly touch each other.
* After the adjustment, securely tighten screws ®, ® and ©.
The needle guard on the rotary hook is to prevent the needle from striking the rotary hook point.
* Be sure to readjust the rotary hook needle guard position when replacing the rotary hook.
2. Needle bar rise and height
Rotary hook
point
Needle
1.5 mm (B837)
2.2 mm (B838)
2.4 mm (8837) ^
2.8 mm (8838) ^
Needle bar rise
(1) Turn the feed adjusting knob to position 0.
(2) Loosen screws O lor lower shaft spiral gearO- and move lower shaftspiral gearO totheright orleft so thatthe rotary
hook pointwill be at the center lineof the needle when the needle rises 2.4 mmwith8837, 2.8 mmwith BBSS from its
lowest position.
* The rotary hook shaft has a screw seat, so the above adjustment cannot be made with the pinion gear.
* When tightening screws O for lower shaft spiral gear O. make sure that it is in line with the screw seat.
Needle bar height
(1) Turn the feed adjusting dial to position 0 (8837) or 4 (8838).
(2) Loosen screws O. and move the needle bar up or down to adjust the clearance between the top of the needle eye and
the rotary hook point to 1.5 mm (8837) or 2.2 mm (8838), when the rotary hook point is in linewith the center of
the needle.
* After the adjustment, tighten screw O securely.
Model
Application
Needle bar rise
Feed control dial
Standard Thread cutter Standard Thread cutter
1 18-837
Thick materials 2.4 mm
2.4 mm 0 0
1 18-838
Thick materials 2.8 mm
0
^ ^
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