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 serve this same purpose.

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

Weaving involves two sets of threads that cross each other. The warp threads are stretched lengthwise on the loom. The weft threads are inserted crosswise, passing over and under the warp. The warp ends are usually fastened to two beams—one at each end—to keep the threads parallel and taut. Weaving starts at one end and moves toward the other. The beam holding the finished fabric is the cloth beam; the other is the warp beam. These beams can act as rollers, allowing the weaver to make cloth longer than the loom itself. As weaving progresses, warp threads unroll from the warp beam, and the woven cloth rolls onto the cloth beam (also called the takeup roll). The unrolled woven section is the fell. Not all looms have two beams: a warp-weighted loom uses a single beam, with warp yarns hanging down 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 between raised and unraised warps—through which the weft can be inserted. Simple shedding, lifting odd and even threads alternately, creates a tabby weave. More complex sequences produce weaves like twill. Picking is passing the weft through the shed; each crossing is a pick. Conventional shuttle looms run at about 150 to 160 picks per minute. Battening presses each new weft thread against the fell, preventing gaps in the fabric. Two secondary motions are also common: taking up winds the new fabric onto the cloth beam, while letting off releases warp from the warp beam. An automatic loom also needs a tertiary motion—a filling stop motion—that brakes the loom if the weft thread breaks. Such looms require 0.125 to 0.5 horsepower (100 to 400 watts) to operate.

A typical loom has two beams held apart, plus components to aid shedding, picking, battening, and taking up. The frame and these devices vary widely. Looms are specialized for different weaves and for the weaver’s lifestyle: nomadic weavers prefer light, portable looms, while those in cramped homes might use tall upright looms or ones that fold away.

Manual threading of weft over and under warp is slow, so most weaving uses shedding devices. These pull some warp threads aside to form a shed. At least two sheds (shed and countershed) are needed for tabby weave; more complex weaves like twill, satin, diaper, or figured weaves require more sheds. Some techniques, like tapestry and knotted-pile carpet, use manual shedding or none at all, because the slow pace of color changes or knotting makes faster shedding unnecessary. Heddle-rods and shedding-sticks are simple to make from sticks and yarn, and are common on vertical and backstrap looms. They allow elaborate brocades and are also used on modern tapestry looms. At its simplest, a heddle-bar is a stick placed across the warp and tied to individual threads.