typical GT1790A, Instruction Book

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5. Adjusting bobbin thread tension
Adjust the bobbin thread tension as given below when the bobbin thread is pulled up at the position where thread
slit
❶
of bobbin case comes up.
Purl stitch 0.05
〜
0.15N
Hold the thread end coming from the bobbin case with hand, shake it up and
down lightly and the bobbin case will drop slightly.
Whip stitch 0.15
〜
0.3N
Hold the thread end coming from the bobbin case with hand, shake it up and
down a little more strongly and the bobbin case will drop.
When turning the thread tension screw
❷
clockwise, the bobbin thread tension will be increased, and turning it
counterclockwise, the bobbin thread tension will be decreased.
For synthetic thread, reduce the tension slightly. For cotton thread, please increase the tension slightly. Increase
the thread tension by around 0.05N after the hook has been installed because an anti-spin spring has been installed
in the machine.
Caution When bobbin thread tension is adjusted, check the needle thread tension setting of the memory
switch. (Refer to “V-22. List of memory switch data” p.52)
6. Installing bobbin case
! Warning
Please turn off the power switch and confirm that the motor has stopped before operation to
prevent personal injuries caused by unexpected start.
1) Raise the bobbin case latch lever.
2) Push the bobbin case into the hook so that it is
supported by the hook shaft
❶
and then snap the
latch lever. Press the bobbin case until the
predetermined position is reached, it will click.
1. If the bobbin case is not in the required
position, it can jump out from the hook
to cause the needle thread to tangle on
the hook shaft. Check to be sure that the
bobbin case is properly installed in the
correct position.
2. Because shapes of standard hook and
dry-type hook are different, any type of
hook cannot be replaced by the other.