Take-up is the shortening of yarns during weaving because of the curving of the threads as they interlace. For example, larger yarns take up more than finer ones because they must travel farther in their curves that go over and under the weft. When the separate warps take-up differently, they cannot be put together on a single beam. Read the sections that follow for what to do if you have one beam or two.
Differences in Take-up: When the Two Warps Must Be Tensioned Separately
If the two warps have different take-up, they cannot be put on a single beam because one would become tight and the other would sag as the weaving progressed until a clean shed was impossible. Sometimes you can get by with beaming all the threads on one warp beam when the warp is short. The longer the warp, the more the differences listed below can interfere with the cloth that you planned.
If you have only one beam, one of the warps is weighted separately. The procedure is described in this chapter. When the take-up could be different
Threading Two Warps
The two warps are threaded at one time by selecting the threads for the heddles from each warp’s lease as needed. This is easy to do when you set up the two warps one above the other, with the leases clearly in view.
Each warp has its own lease sticks or lease cords and each is hung over its own broomstick for threading. Hang them with one a little above the other so the leases hang suspended from the broom handles and you can see each lease from your threading position. See Figure. I usually have the main warp on the lower lease sticks and the supplementary one above it. Since threading is more complicated with two warps, it’s most important to be comfortable.
If your extra warp is weighted separately and not on its own beam, anchor it to the back beam with a tight choke tie while you thread. This gives you something to pull against while threading so you don’t tangle the remaining warp.
Taken from Book 2: “Warping Your Loom and Tying On New Warps“