|In weft-faced fabrics, the warp is all but covered by the weft. To accomplish this, you have to space the warps far enough apart that the rows of weft will pack down and cover them. There is a method which can be used as a starting point for experimentation in finding this warp spacing. Use your ruler to wind both the warp and the weft threads together. Alternate the warp and weft threads. Keep them flat. Be careful not to twist or stretch them, but still, push them together until they just barely touch. Finally, count only the warp threads in your inch to get the approximate sett. See Figures A-C. You probably will use a thicker weft yarn than a warp yarn.
In warp-faced fabrics, there are so many more warp threads than weft threads that the weft is all but covered by the warp. Use Ashenhurst’s diameters or wrap the warp threads around your ruler. Then, increase or even double the number per inch you get. See figure below.
If you want a true plaid, then you’d want a precisely balanced sett, so that the warps and wefts are both showing equally. However, look at a machine woven plaid-the warps are denser than the wefts-for ease in weaving.
If a weave has weft emphasis, you can’t have the warp as dense as 80%. Examples are overshot and summer-and-winter fabrics. Use a plain weave sett here because plain weave is the basis for these two weaves. Then, as a starting point, take 60-70% of their maximum sett, depending on the purpose of your cloth.
More information in Weaving for Beginners and Book #1: Winding a Warp & Using a Paddle