Brother b831 Service Manual page 59

BB Needle to Rotary Hook Timing
Rotary hook point
Needle
Needle guard
0.05—0.1 mm
>1
•Needle
-j- 1.5 mm
I j 2.4 mm
Remove the needle plate and feed dog, and set the feed dial to 0.
The needle to rotary hook point gap should be 0.05 to 0.1 mm. Loosen set screws O. O. ©. and adjust the horizontal
position of the rotary hook base O to adjust the gap.
Adjust the needle guard so the needle lightly contacts the needle guard after adjusting the gap.
Firmly tighten set screws O- O. O after the adjustment is completed.
Needle Bar Lift Stroke
* The rotary hook point should be aligned with the needle center when the needle is raised 2.4 mm from the down
position. Loosen the lower shaft gear 0 set screw O and shift the lower shaft gear 0 horizontally to adjust.
* The screw stop on the rotary hook shaft prevents alignment using the pinion gear.
* Tighten the set screw 0 of the lower shaft gear 0 without changing the screw stop used.
Needle Bar Height
* The needle hole edge to rotary hook point gap should be 1.5 mm when the rotary hook point is aligned with the needle
center. Loosen screw 0 and adjust the vertical needle bar position to adjust.
* Firmly retighten screw 0 after the adjustment is completed.
* The rotary hook bushing determines the height of the rotary hook complete. The rotary hook complete to needle plate
gap is a fixed distance (1.2 mm).
HB Bobbin Case Opener Adjustment
0.2 mm
1. Install the feed dog and needle plate.
2. Firmly tighten the bobbin case opener O in place with set screw 0.
3. The rotary hook 0 tobobbin caseopener O gapshould be0.2 mm when thebobbin caseopener 0 is pulled all theway
inthe direction of the arrow. Loosen screw 0 and adjustthe horizontal position of the bobbin case opener O to adjust
the gap.
* Be sure to firmly retighten screw 0 when the adjustment is completed.
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