I'm a beginning weaver with a rigid-heddle loom. I'm having trouble keeping the width of a piece the same. When I weave scarves, they get narrower and narrower as I go. The width at the end can be as much as two inches narrower than at the beginning. What am I doing wrong?
Your problem is one that we have all faced as beginning weavers. If you place the weft straight across in the shed and then beat, the weft has to change from being straight to curving over and under the warp threads. To do this, it will have to pull the warp threads closer together.
If you were weaving on a shaft loom and inserted the weft straight across, eventually you would end up breaking warp threads. Warp tension on shaft looms has to be tighter than on a rigid-heddle loom, and when the reed hits the cloth as you beat, the reed's teeth can become like knives and cut the edge threads. Looser warp tension on the rigid-heddle loom and the gentler pressing rather than beating that one usually does on these looms allows the warp threads to bend as the heddle reaches the cloth. So while the warp threads don't usually break, the cloth narrows.
On both types of looms, however, the key to a consistent weaving width and minimal wear and tear on edge warp threads is providing enough weft allowance. That is, the length of weft actually placed in the shed needs to be longer than the width of the warp by ten percent or more. (This is with balanced weaves such as twills and plain weave and weaves with a plain-weave base.)
There are several ways to accomplish this, but the most foolproof is to place the weft at about a thirty degree angle. For a shaft loom and relatively smooth threads I advise closing the shed before beating to make sure the weft angle isn't pulled flat as you beat. On the rigid-heddle loom, this isn't necessary; you are less likely to pull on the weft with the hand holding the shuttle as you "beat."