The principles of how warps and wefts bend are valuable to understanding a lot about weaving–especially why cloth draws in and causes selvedge threads to break.
The principles apply for so many aspects–for example, for weaving balanced or near balanced fabric, the warp tension must not be too tight. That would prevent the warps from bending. If the tension is too tight, the warps will be straight and that will force the wefts to do all the bending. Besides draw-in problems, the cloth will be more weft face with the wefts beaten down more than for a balanced look.
The warp tension should be just enough to get a shed for fabric that has a balanced look. So many students I see have the tension much too tight. Tight tension is only desirable for weft faced textiles. (Then you must bubble the weft or the draw-in will be too much.)
Here’s how the bending works in different sett (epi) situations,
and how it affects your cloth’s draw-in.
Balanced plain weave is shown in Figure 518a.
“Balanced” means there are the same number of warps per inch (epi) as wefts per inch. You can see that both the warps and the wefts bend or curve. The diagonal of the wefts in the sheds
provides the slack needed to allow for the wefts to bend. The warps bend after the cloth is taken off the loom when there is no longer any tension on them. Remember, you allowed for this occurrence in planning the length of the warp by adding in an allowance for “take-up.” See page 290.
In weft-faced weaving, the warps are straight and the wefts do all the bending. See Figure 518b. Notice that the warps are farther apart than for balanced plain weave. Fewer ends per inch (epi) force the wefts to bend so much that there needs to be much more weft in the shed than for balanced weaves. To allow for the yarn to bend over and under the warp threads, more diagonal, or
even bubbling of the weft is needed. Read about bubbling on page 128.
In Figure 518c, the warps are very close together (more ends per inch), and they are bending, but the wefts are straight. This is warp-faced plain weave. Warps that close force the wefts to be straight. These warps take up much more than those in balanced weaving do, because they have to curve so much over and under the wefts. Less slack or weft diagonal is needed because the wefts are straight and do not bend.