Looms & Weaving Techniques

Weaving

Weaving is a textile craft in which two distinct sets of yarns or threads, called the warp and the filling or weft (older woof), are interlaced to form a fabric or cloth. The warp threads run lengthways on the piece of cloth, and the weft runs across from side to side, across the bolt of cloth Weaving is done by intersecting the longitudinal threads, the warp, i.e. "that which is thrown across", with the transverse threads, the weft, i.e. "that which is woven".

The way the warp and filling threads interlace with each other is called the weave. The majority of woven products are created with one of three basic weaves: plain weave, satin weave, or twill. Woven cloth can be plain (in one colour or a simple pattern), or can be woven in decorative or artistic designs, including tapestries. Fabric in which the warp and/or weft is tie-dyed before weaving is called ikat. The ancient craft of handweaving, along with hand spinning, remains a popular craft. The majority of commercial fabrics in the West are woven on computer-controlled Jacquard looms. In the past, simpler fabrics were woven on dobby looms, while the Jacquard harness adaptation was reserved for more complex patterns. Some believe the efficiency of the Jacquard loom, with its Jacquard weaving process, makes it more economical for mills to use them to weave all of their fabrics, regardless of the complexity of the design.

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In general, weaving involves the interlacing of two sets of threads at right angles to each other: the warp and the weft. The warp are held taut and in parallel order, typically by means of a loom, though some forms of weaving may use other methods. The loom is warped (or dressed) with the warp threads passing through heddles on two or more harnesses. The warp threads are moved up or down by the harnesses creating a space called the shed. The weft thread is wound onto spools called bobbins. The bobbins are placed in a shuttle that carries the weft thread through the shed. The raising and lowering sequence of warp threads gives rise to many possible weave structures:
 
plain weave, twill weave, satin weave, and complex computer-generated interlacings. 
 
Both warp and weft can be visible in the final product. By spacing the warp more closely, it can completely cover the weft that binds it, giving a warpfaced textile such as rep weave. Conversely, if the warp is spread out, the weft can slide down and completely cover the warp, giving a weftfaced textile, such as a tapestry or a Kilim rug. There are a variety of loom styles for hand weaving and tapestry. In tapestry, the image is created by placing weft only in certain warp areas, rather than across the entire warp width.

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Loom is a device used to weave cloth. 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 major components of the loom are the warp beam, heddles, harnesses, shuttle, reed and takeup roll. In the loom, yarn processing includes shedding, picking, battening and taking-up operations. 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 or heald frame, also known as a harness. This is a rectangular frame to which a series of wires, called heddles or healds, 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. Two common methods of controlling the heddles are dobbies and a Jacquard Head.  Picking. As the harnesses raise the heddles or healds, 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. The point where the fabric is formed is called the fell. 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. To become fully automatic, a loom needs a filling stop motion which will brake the loom, if the weft thread breaks.  An automatic loom requires 0.125 hp to 0.5 hp to operate. From 1942 the faster and more efficient shuttleless Sulzer Looms and the rapier looms were introduced. Modern industrial looms can weave at 2000 weft insertions per minute. 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. Projectile and rapier looms eliminated the need to take the bobbin/pirn of thread through the shed;  Dobby Loom is a type of floor loom that controls the whole warp threads using a device called a dobby. Dobby is short for "draw boy" which refers to the weaver's helpers who used to control the warp thread by pulling on draw threads. 

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A dobby loom is an alternative to a treadle loom. Each of them is a floor loom in which every warp thread on the loom is attached to a single shaft using a device called a heddle. A shaft is sometimes known as a harness, but this terminology is becoming obsolete among active weavers. Each shaft controls a set of threads. Raising or lowering several shafts at the same time gives a huge variety of possible gaps or 'sheds' through which the shuttle containing the weft thread can be thrown. A manual dobby uses a chain of bars or lags each of which has pegs inserted to select the shafts to be moved. A computer assisted dobby loom uses a set of solenoids or other electronic devices to select the shafts. Activation of these solenoids is under the control of a computer program. In either case the selected shafts are raised or lowered by either leg power on a dobby pedal or electric or other power sources. On a treadle loom, each foot-operated treadle is connected by a linkage called a tie-up to one or more shafts. More than one treadle can operate a single shaft. The tie-up consists of cords or similar mechanical linkages tying the treadles to the lams that actually lift or lower the shaft.

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On treadle operated looms, the number of sheds is limited by the number of treadles available. An eight shaft loom can create 254 different sheds. There are actually 256 possibilities which is 2 to the eighth power, but having all threads up or all threads down isn't very useful. However, most eight shaft floor looms have only ten to twelve treadles due to space limitations. This limits the weaver to ten to twelve distinct sheds. It is possible to use both feet to get more sheds, but that is rarely done in practice. It is even possible to change tie-ups in the middle of weaving a cloth but this is a tedious and error-prone process, so this too is rarely done. With a dobby loom, all 254 possibilities are available at any time. This vastly increases the number of cloth designs available to the weaver. The advantage of a dobby loom becomes even more pronounced on looms with 12 shafts (4094 possible sheds), 16 shafts (65,534 possible sheds), or more. It reaches its peak on a Jacquard loom in which each thread is individually controlled.

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Another advantage to a dobby loom is the ability to handle much longer sequences in the pattern. A eaver working on a treadled loom must remember the entire sequence of treadlings that make up the pattern, and must keep track of where they are in the sequence at all times. Getting lost or making a mistake can ruin the cloth being woven. On a manual dobby the sequence that makes up the pattern is represented by the chain of dobby bars. The length of the sequence is limited by the length of the dobby chain. This can easily be several hundred dobby bars, although an average dobby chain will have approximately fifty bars.

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A computer controlled dobby loom (Computer-Dobby) takes this one step further by replacing the mechanical dobby chain with computer controlled shaft selection. In addition to being able to handle sequences that are virtually unlimited, the construction of the shaft sequences is done on the computer screen rather than by building a mechanical dobby chain. This allows the weaver to load and switch weave drafts in seconds without even getting up from the loom. In addition, the design process performed on the computer provides the weaver with a more intuitive way to design fabric; seeing the pattern on a computer screen is easier than trying to visualize it by looking at the dobby chain.

Dobby looms expand a weavers capabilities and remove some of the tedious work involved in designing and producing fabric. Many newer cloth design techniques such as network drafting can only reach their full potential on a dobby loom.

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Historical Note: Dobby looms first appeared around 1843 -- roughly forty years after M. Jacquard  invented the Jacquard device that that can be mounted atop a loom to lift the individual heddles and warp threads.