Adjustment Of Bobbin Thread Tension - Pfaff Select 1520 Service Manual

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:
When a threaded bobbin case hangs on its thread, it must not slide downwards by its own weight.
Upon sharp upward movements of the hand, the thread must run off gradually (fig. 73).
There must not be any thread waste under the tension spring.
The tension spring must rest evenly and parallel on the bobbin case.
Adjustment:
Loosen the knurled screw a little and turn it in again until a resistance is felt when the thread is pulled
off.
Cross-check:
As described under "Check".
Note:
Once the bobbin thread tension has been set correctly, tension adjustments should be made only on
the needle thread tension.
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