Brother bas-311hn Instruction Manual page 68

9. TROUBLESHOOTING
Problem
Lower thread winds to
one side.
Lower thread winding
amount is incorrect.
Thread unraveling at
sewing start.
Skipped stitches occur.
60
Cause
Height of bobbin winder tension
assembly is incorrect.
Bobbin presser position is incorrect.
Needle is too thick.
Upper thread trailing length is too short.
Amount of lower thread being fed out
from bobbin is too small.
Sewing start speed is too fast.
Rotary hook tip is missing.
Needle is too thin.
Needle is too thick.
Needle is bent.
Needle is not installed correctly.
Needle and rotary hook tip are
touching.
Clearance between needle and rotary
hook tip is too large.
Needle and rotary hook timing is
incorrect.
Material is flapping.
BAS-311HN, BAS-326H
Remedy
Adjust the height of the bobbin winder
tension assembly.
Adjust the position of the bobbin
presser.
Select a needle that is suitable for the
sewing conditions.
When threading the thread through the
needle, allow a distance of
approximately 42 mm between the
needle hole and the end of the thread.
Adjust the sub-tension so that the
upper thread trailing length after thread
trimming is approximately 42 mm.
Set the feeding amount to
approximately 30 mm.
Adjust the sewing start speed.
Replace the part.
Select a needle that is suitable for the
sewing conditions.
Replace the needle.
Install the needle so that it faces
correctly.
Adjust the driver needle guard.
Adjust the needle clearance.
Adjust the timing.
Replace the needle hole plate with one
with a smaller needle diameter.
Use a thinner feed plate.
* Recommended thickness: 1.5 mm
Process the work clamps and the feed
plate into shapes that can hold the
material near the seam.
Adjust the intermittent height of the
intermittent presser foot.
Reference
P. 26
P. 26
P. 28
P. 23
P. 29
P. 27
*
P. 28
P. 22
P. 22
P. 41
P. 41
P. 40
P. 51
P. 52
*
(Continued on next page)