Negative Let-Off Mechanism

Negative let-off is a mechanism for controlling the rotation of the beam on a weaving, warp knitting or other fabric forming machine where the beam is pulled round by the warp against a breaking force applied to the beam.

Main parts:
1. Warp beam.
2. Beam ruffle.
3. Chain.
4. Machine frame.
5. Weight lever.
6. Pivot.
7. Fulcrum.
8. Weight.

Let-off mechanism:
The warp beam ruffle is wrapped around by chain. The one end of the chain is fixed at . i.e. at the m/c frame whereas the other end is connected to fulcrummed device to the weight lever , which is pivoted  and a dead weight  is placed which can be moved along the length of the weight lever.

In this system the tension of the warp is regulated by the friction between chain and the beam ruffle. The friction is controlled by dead weight on the weight lever and the distance of deadweight from the pivot. Heavier the dead weight and longer the distance of it from the pivot lesser the let-off.

The warp beam dia gradually decreases as weaving proceeds. So it’s necessary to increase the let-off rate. If the dead weight is kept on the same place, the let-off rate will remain unchanged. So an experienced worker is required to change the dead weight gradually with the change of the warp beam dia. As a result irregular tension occurs and the rate of yarn breakage may increase.

Conclusion:
Negative let-off mechanism is a very simple and manual mechanism. It is suitable for light and medium weight fabrics. It is mainly used in old looms and for weaving of plain cotton fabric

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