Shed (weaving)

Depending on the type of loom, different devices are used to raise and lower the shed. With a tablet loom, the sheds are raised and lowered by rotating the tablets, or cards. With a floor loom, the shed is created by the harnesses. Inkle looms have one of the more primitive shedding devices, where there is one set of heddles and the shed is created by hand. with a shed-rod Originally there was no shed, and the weft was inserted into the warp by picking the warp threads up individually, as is done in tapestry weaving. After each weft thread is woven the warp threads had to be picked out and lifted again, which made the process slow. To speed up the process various devices were developed to create a reproducible shed, so that the weft could be passed between the separated threads, and so the threads would not have to be separated individually each time. The first type of shedding device was called a shed-rod. It was a rod inserted into the warp to ease in weaving, and came about at the same time as the heddle. Threads were alternated over and under the rod, and the threads that went under the rod went through string heddles attached to a bar. The shed was created in two ways: by raising the shed-rod, and by lifting the heddles. After the shed-rod came the rigid heddle loom, where the shed is created by raising or lowering the rigid heddle. As the loom progressed, the shed-rod was replaced by a second set of heddles, for a total of two shafts with heddles. Eventually looms like the modern floor loom were developed, where there are many shafts which can be raised to create the shed. == Rising shed loom ==

Two different shedding methods were developed for the harness loom-one where any one harness or combination of harnesses was lifted while the other harnesses remained stationary. This type of loom is known as a rising shed loom, and examples include the table loom, dobby loom or the Jack loom. The other method used in harness looms is where some harnesses are raised while others are lowered. The second method lessened the effort of lifting the selected harnesses because they no longer needed to be raised as high as in a rising shed loom. Counterbalance and countermarch looms are of this second type. == Poor shed ==

There are many things that can cause the warp threads not to separate cleanly, and thus produce a poor shed. A slack warp, threads set too closely in the reed, or increase of friction on the first foot or so of the warp where the threads were handled all cause poor sheds. Fuzzy yarns like mohair can also cause a poor shed. To get a better shed the weaver can lift the harnesses while the reed is against the fabric, or raise only one harness at a time. By weaving in a different manner sometimes a good shed can be created. The weaver can also insert a stick into the shed to clear it, and make way for the shuttle though this option is time-consuming. == References ==