Delta MD 11871 Manual page 24

Adjusting the lower thread tension
The lower thread tension rarely needs to be adjusted, as it was
setting by the manufacturer for general sewing work.
The lower thread tension is correct if you can pull the thread out
of the bobbin easily but with a slight resistance.
However, the lower thread needs to be adjusted for particularly
lightweight or heavy fabrics.
You set the lower thread tension by using the regulating screw
on the bobbin case. Adjust the screw using the small
screwdriver provided.
Remove the bobbin case:
Low tension:
Higher tension:
Checking the lower thread tension
The easiest way of checking the lower thread tension is by sewing a medium
zigzag stitch on the fabric in question.
Use the appropriate needle and threads.
You can get a clearer picture by using different colours for the upper and lower
threads.
Sew a few zigzag stitches.
The thread tension is correct if the lower threads are not visible on the top surface
of the fabric.
Make sure that you always sew even stitches (see diagram on the left).
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Model Number: MD 11871
Stitch type
selection dial
8
9
Turn the screw anticlockwise
Turn the screw clockwise.
Stitch
Stitch length
regulator
Elastic
1
+
decorative
-
stitch
Stretch-
1
overlock +
-
(elastic)
Double-
1
+
overlock
-
(elastic)
Upper
thread
tension
-
2 - 6
-
2 - 6
-
2 - 6
26