67
36. Adjustment of bobbin thread tension
Requirement:
The force required for pulling cotton thread 50/2 or synthetic fiber thread 100/3 off the bobbin must be
approximately 20-25 g.
Check:
z When a threaded bobbin case hangs on its thread, it must not slide downwards by its own weight.
z Upon sharp upward movements of the hand, the thread must run off gradually (fig. 73).
z There must not be any thread waste under the tension spring.
z The tension spring must rest evenly and parallel on the bobbin case.
Adjustment:
z Loosen the knurled screw a little and turn it in again until a resistance is felt when the thread is pulled
off.
Cross-check:
z As described under "Check".
Note:
z Once the bobbin thread tension has been set correctly, tension adjustments should be made only on
the needle thread tension.
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