Dobby loom

A Dobby loom is a type of floor loom that controls all the warp threads using a device called a dobby. (The word dobby is a corruption of "draw boy" which refers to the weaver's helpers who used to control the warp thread by pulling on draw threads.) A dobby loom is an alternative to a treadle loom. Both are floor looms 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. Each shaft controls a set of threads. Raising or lowering several shafts at the same time gives a huge variety of possible sheds (gaps) through which the shuttle containing the weft thread can be thrown.

Dobby looms first appeared around 1843, roughly 40 years after Joseph Marie Jacquard invented the Jacquard device that can be mounted atop a loom to lift the individual heddles and warp threads.

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 electric 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.

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 is not very useful. 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 this 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 process, so this too is rarely done.

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