lock off

When a length of woven fabric comes off the loom, the warp threads that run lengthwise through the cloth are still under tension and liable to slip loose at the selvedge or cut edge. Locking off means turning or twisting those exposed warp strands back into the fabric structure itself, binding them mechanically so they cannot pull free and cause the cloth to unravel during subsequent handling, finishing, or use.

The method depends on fabric type and loom configuration. On shuttle looms, operators may turn warp ends by hand or use a simple hand tool to twist threads back into the selvage edge; on modern rapier or air-jet looms, locking off is often performed as a finishing operation after the cloth is removed. Some mills twist the threads into a tight spiral; others loop them back and stitch them down with thread or temporary adhesive. The key is creating enough friction and mechanical interlocking that the warp cannot slide out under the tension of normal handling.

Poor locking off shows up quickly in quality control. Unraveling begins within days or weeks depending on how the cloth is stored or transported, starting at the cut edge and working backward along the length. This is especially problematic for natural fibers like cotton and wool, which show the defect more visibly than synthetics, and for lightweight fabrics where the selvedge is naturally delicate.

The term comes directly from the action: the warp thread is locked off from its tension and its escape route. It is distinct from other edge-finishing methods such as binding or hemming, which cover the edge; locking off preserves the edge structure itself. It is also routine maintenance rather than a defect correction, performed at the mill as standard procedure before cloth ships to finishing plants or customers.