scob

A scob is a weaving defect where the weft yarn fails to interlace properly with a sequence of warp threads, creating a gap or slack area in the cloth. Instead of passing over and under the warp in its proper sequence, the weft thread either floats across several warps without binding, or the weft picks skip entirely, leaving those warp threads unwoven. The result is a visible disturbance in the fabric surface, usually appearing as a thin horizontal line or hollow where the weft should have secured the weave.

Scobs range from single-pick faults, where one weft shot misses one or two warps, to multi-pick defects spanning several centimetres of cloth width. A scob affecting only a few warp ends may go unnoticed in heavy cloth but is immediately apparent in fine or transparent weaves. The defect is distinguished from other weft faults by the deliberate or mechanical nature of the skip rather than a break in the yarn itself.

Scobs most commonly result from mechanical failure in the loom's weft insertion mechanism. On shuttle looms, a bent reed or a dull shuttle point may cause the weft to deflect mid-pick. On modern projectile, rapier, or air-jet looms, misalignment of the weft guide, blocked needle eyes, or timing errors between weft insertion and warp shed movement are typical culprits. Tangled or slubbed weft also increases risk, as the thickened yarn may jam in the reed opening and be carried over uninserted warp ends.

Preventive maintenance focuses on keeping the reed straight, checking for burrs on shuttle points or guides, and ensuring precise timing synchronisation between the weft insertion device and the loom's main motion. Regular inspection of warp tension and shed opening geometry reduces the likelihood of weft missing its target.

Quality control staff identify scobs during cloth inspection by holding fabric to light and running a hand across the surface to feel discontinuities. Depending on the cloth grade and market, a single scob may render that piece unsuitable for sale, requiring either careful repair by hand or classification as second quality.