Loom

A loom is a tool for making cloth and tapestry by weaving. Its core job is to keep the warp threads taut so the weft threads can be woven between them. While looms come in many shapes and use different mechanisms, they all work on this same principle.

The word "loom" comes from Old English *geloma*, meaning any tool or machine. By 1404, "lome" specifically referred to a machine for weaving thread into cloth, and by 1838, it had gained the additional meaning of a machine for interlacing thread.

Weaving uses two sets of threads that cross each other. The warp threads are stretched lengthwise on the loom, while each weft thread is inserted over and under the warp. The warp ends are usually fastened to two beams—one at each end—to keep them parallel and taut. The beam holding the finished fabric is the cloth beam; the other is the warp beam. These beams can act as rollers, letting the weaver make cloth longer than the loom itself. As weaving progresses, warp threads unroll from the warp beam, and the woven fabric rolls onto the cloth beam. The section of fabric not yet rolled up is called the fell. Not all looms have two beams: warp-weighted looms, for example, have only one, with warp yarns hanging from it and weighted at the bottom.

A loom performs three main motions: shedding, picking, and battening. Shedding pulls some warp threads aside to create a shed—the gap through which the weft is inserted. Simple shedding, like lifting odd and even threads alternately, produces a tabby weave; more complex sequences create twill and other weaves. Picking is passing the weft through the shed; each crossing is called a pick. Conventional shuttle looms run at about 150 to 160 picks per minute. After each pick, battening presses the new weft thread against the fell to prevent gaps. Two secondary motions—taking up the finished cloth onto the cloth beam and letting off warp from the warp beam—are also needed. For full automation, a tertiary motion, the filling stop motion, brakes the loom if the weft breaks. An automatic loom requires 0.125 to 0.5 horsepower (100 to 400 watts) to operate.

A loom typically needs two beams held apart, plus components to aid shedding, picking, battening, and taking up the fell. The frame and these devices vary widely, with many looms specialized for certain weaves or weavers' lifestyles. Nomadic weavers often use lighter, portable looms, while those in cramped city dwellings may prefer tall upright looms or ones that fold away.

Manual weaving—threading the weft over and under warp by hand—is slow, so most looms use shedding devices. These pull warp threads aside to form at least two sheds (the shed and countershed), enough for tabby weave. More complex weaves like twill, satin, diaper, or figured weaves require more sheds. Some techniques, like tapestry or knotted-pile carpet weaving, use manual shedding or no shedding for the pile, as the slow handwork makes faster shedding systems unnecessary. Heddle-bars and shed-rods are simple shedding methods, made from sticks and yarn, often used on vertical, backstrap, or tapestry looms. A heddle-bar is a stick placed across the warp and tied to individual threads.