Brother BAS-311H Instruction Manual page 87

Problem
Upper thread is not
tight.
0573M
Lower thread is not
tight.
0574M
Uneven thread
tightening at the sewing
start.
Poor seam finish on
underside of material at
the sewing start.
Upper thread trailing
length is irregular.
Cause
Needle is too thin.
Hole diameter in needle hole plate is
too small.
Feed plate is too thin.
Hole diameter of intermittent work
clamp is too small.
Sliding parts of outer rotary hook and
inner hook have little or no sewing
machine oil.
Damage or burring in parts such as the
rotary hook, needle hole plate, needle
or thread path.
Lower thread tension is too strong.
Upper thread tension is too weak.
Thread take-up spring tension is too
weak.
Feed timing is too fast.
Intermittent height of intermittent work
clamp is too low.
Needle and rotary hook
touching.
Lower thread tension is too weak.
Upper thread tension is too strong.
Bobbin spinning
Upper thread trailing length is too long.
Movable knife is blunt.
Fixed knife is blunt.
Sub-tension is too weak.
Thread take-up spring tension is too
weak.
Select a needle that is suitable for the
sewing conditions.
Replace the needle hole plate with one
with a larger hole diameter.
Use a thicker feed plate.
*Recommended thickness: 1.5 mm
Replace the intermittent work clamp
with one with a larger hole diameter.
Lubricate the felts for the sliding parts
of the outer rotary hook and inner hook.
Repair the respective part by buffing it.
Alternatively, replace the part.
Reduce the lower thread tension.
Increase the upper thread tension.
*Adjust the upper thread tension after
adjusting the lower thread tension.
Increase the tension of the thread
take-up spring.
Retard the feed timing.
Adjust the intermittent height of the
intermittent work clamp.
Adjust the driver needle guard.
tip are
Adjust the needle clearance.
Increase the lower thread tension.
Reduce the upper thread tension.
*Adjust the upper thread tension after
adjusting the lower thread tension.
Use an anti-spin spring.
Adjust the sub-tension so that the
upper thread trailing length after thread
trimming is approximately 40 mm.
Replace the movable knife with a new
one.
Sharpen the fixed knife or replace it
with a new one.
Adjust the sub-tension.
Increase the tension of the thread
take-up spring.
BAS-311H
12. TROUBLESHOOTING
Remedy Reference
P. 26
P. 20
P. 26
P. 26
P. 56
P. 38
P. 57
P. 58
P. 26
P. 26
P. 26
P. 61
P. 61
P. 26
P. 56
78