harness
The part of a loom comprising the heddles, with their means of support and motion, by which the threads of the warp are alternately raised and depressed for the passage of the shuttle.
harness: the warp-lifting mechanism inside a loom
In weaving, a harness is the assembly of heddles, frames, and linkages that controls which warp threads rise and fall with each pick of the shuttle. On a floor or power loom, the harness sits above the weaving plane and connects to a treadle (foot-operated) or cam (mechanical) drive that cycles it up and down. This vertical motion creates the shed, the triangular opening through which the shuttle passes, carrying the weft thread across the warp.
A harness typically consists of a wooden or steel frame holding multiple heddles, which are wire or cord loops. Each heddle grips one warp thread at its eye, a small opening near the center. By raising certain heddles while lowering others, the weaver or machine selects which threads stay down and which lift. The pattern of which heddles lift on each pick determines the cloth structure, whether plain weave, twill, satin, or a jacquard pattern.
Harness shafts and complexity
Simpler looms use two or four harnesses, one per shaft; raising shaft one while lowering shaft two creates a basic shed. Dobby and jacquard looms employ many more shafts, up to 32 or beyond, each with its own harness. The harness bars (the frame members) are usually hardwood like maple or ash, chosen for stiffness and resistance to wear. Heddles themselves are made from polished wire, twisted nylon cord, or (in older looms) from linen thread wound around wire frames.
Wear and timing are critical. Heddles degrade from abrasion against the warp threads and may snap, creating dropped stitches downstream. The heddles must all rise and fall by the same amount at the same instant, or the shed will be uneven and the shuttle may catch. Adjustments to harness height, heddle spacing, and timing require mechanical skill and are often made during loom setup or troubleshooting.
The term harness comes from its function of harnessing or controlling the warp threads. In the wider textile hierarchy, the harness is one component of the shedding motion, which also includes the cams, linkages, and treadles that drive the harness. Understanding harness design and condition is essential for production engineers tuning loom performance and for technicians diagnosing weave defects or loom stoppages.