Brother XM3700 Service Manual page 189

Adjustment
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8. Pull down the BH lever to the downmost, and then switch the position to the rear side by pushing the BH lever
from the front to the rear.
9. Set the BH foot.
10. Attach the foot controller, and turn on the power.
11. Execute the bar tack sewing to the double broadcloth with a schappe spun thread #60, and check the number of
stitches of the left reverse stitch and right forward stitch.
*Key point
• Sew the bar tack of the buttonhole till the last. (Fig. 1 "1")
When this sewing is stopped halfway, the next bar tack of the buttonhole is not sewn correctly.
BH lever
12. Loosen the nut 4 of the adjusting screw of the BHF finger assy.
13. Adjust the stitch length of the left reverse stitch by turning the adjusting screw of the BHF finger assy.
*Key point
• The number of left reverse stitch/right forward stitches should be 35 to 50 stitches per 20 mm. And the stitch
difference should be within ±10 stitches.
*Key point
• Loosen the adjusting screw. (Turn to the direction "A")
→ Left reverse stitch length is shorter. (The number of stitches increases) (Fig. 2 "A")
• Tighten the adjusting screw. (Turn to the direction "B")
→ Left reverse stitch length is longer. (The number of stitches decreases) (Fig. 2 "B")
14. Tighten the nut 4 of the adjusting screw of the BHF finger assy to secure the adjusting screw.
*Key point
• When tightening the nut 4 of the adjusting screw, keep the adjusting screw from moving.
Nut 4
Adjusting screw
Left reverse stitch of buttonhole stitch length
BH foot
NG
NG
Flat screwdriver
4 - 36
Schappe spun thread #60
Check
Fig. 1
Broadcloth (double)
OK
A
b
b
B
b
b = 35 - 50 stitches
and
The stitch difference of
"b" and "d" is within 10 stitches.
Fig. 2
Check
1
d 20 mm