A loom is a machine or device for weaving thread or yarn into textiles. Looms can range from very small hand-held frames, to large free-standing hand looms, to huge automatic mechanical devices. A loom can also refer to an electrical cable assembly or harness such as a wiring loom.
In practice, the basic purpose of any loom is to hold the warp threads under tension to facilitate the interweaving of the weft threads. The precise shape of the loom and its mechanics may vary, but the basic function is the same.
The earliest attestation of loom with its specific meaning quoted by the Oxford English Dictionary is from the Nottingham Records of 1404, but handwoven cloth existed much earlier, perhaps as far back as 8000 BC.
Handweavers today tend to use looms with at least four shafts or harnesses. Each shaft contains a set of heddles through which yarn can be threaded (and attached, through a variety of mechanisms, to the front and back beams of the loom), and by raising the harnesses in different combinations, a variety of patterns can be achieved. Looms with two such shafts are used for weaving tabby or even weave fabrics. Multishaft looms with eight, twelve, sixteen or more shafts are available.
The shafts on a floor loom are controlled by a series of pedals called treadles. This is an important development, since it keeps the weaver's hands free to manipulate the shuttle and it is easy to raise and lower warp threads in selected combinations. As the fabric is woven it is rolled around the cloth beam, as unwoven warp or yarn is unrolled from the warp beam, so the length of the weaving is not limited by the size of the loom. A table loom is similar, but, as the name suggests, it is smaller and equipped with hand levers rather than treadles, since it is made to sit on a stand or on top of a table.
A computer assisted loom has no actual treadles as the computer program dictates which harness or shaft is lifted, either by a manual pedal or air cylinders, hydraulic cylinders or electric solenoids. A loom that can only lift the shafts is called a rising shed loom or a Jack loom. A loom that can sink and lift the shafts at the same time is either a Counterbalance (CB) loom or a Countermarch loom (CM), these looms are called a sinking shed loom. Most CB looms are a four harness, a CM loom can use many harnesses up to about thirty two harnesses.
A harness is a complete set of loom parts; a lamm, a shaft and an upper harness of cords or jacks. A shaft is a frame which holds a set of heddles which guide some of the warp but not all on one shaft, there is always more than one shaft on a loom.
The first completely automated loom was made by Jacques Vaucanson in 1745. A different power loom was built by Edmund Cartwright in 1785. Originally, powered looms were shuttle-operated but in the early part of the 20th century the faster and more efficient shuttleless loom came into use. Today, advances in technology have produced a variety of looms designed to maximize production for specific types of material. The most common of these are air-jet looms and water-jet looms. Computer-driven looms are now also available to individual (non-industrial) weavers.
Industrial looms can weave at speeds of six rows per second and faster.
Shedding. Shedding is the raising of the warp yarns to form a shed through which the filling yarn, carried by the shuttle, can be inserted. The shed is the vertical space between the raised and unraised warp yarns. On the modern loom, simple and intricate shedding operations are performed automatically by the heddle frame, also known as a harness. This is a rectangular frame to which a series of wires, called heddles, are attached. The yarns are passed through the eye holes of the heddles, which hang vertically from the harnesses. The weave pattern determines which harness controls which warp yarns, and the number of harnesses used depends on the complexity of the weave.
Picking. As the harnesses raise the heddles, which raise the warp yarns, the shed is created. The filling yarn in inserted through the shed by a small carrier device called a shuttle. The shuttle is normally pointed at each end to allow passage through the shed. In a traditional shuttle loom, the filling yarn is wound onto a quill, which in turn is mounted in the shuttle. The filling yarn emerges through a hole in the shuttle as it moves across the loom. A single crossing of the shuttle from one side of the loom to the other is known as a pick. As the shuttle moves back and forth across the shed, it weaves an edge, or selvage, on each side of the fabric to prevent the fabric from raveling.
Battening. As the shuttle moves across the loom laying down the fill yarn, it also passes through openings in another frame called a reed (which resembles a comb). With each picking operation, the reed presses or battens each filling yarn against the portion of the fabric that has already been formed. Conventional shuttle looms can operate at speeds of about 150 to 160 picks per minute.
With each weaving operation, the newly constructed fabric must be wound on a cloth beam. This process is called taking up. At the same time, the warp yarns must be let off or released from the warp beams (Corbman, 1975).