Sett is often discussed in relationship to a balanced plain weave (BPW). A BPW has the same number of warp and weft yarns per square inch. The easiest and most conventional way to guesstimate a BPW sett is to wrap a yarn around a ruler using light tension that mimics how the yarn will behave when relaxed. Count the number of wraps and divide this number by two. By taking half the yarns away, you allow room for the weft to interlace with the warp in equal proportion—assuming you are using the same weight weft.
This is just a place for you to start. You need to take into account the setts available to you, your structure, and the desired look of your fabric, a lacy scarf requires different materials and sett than a mat. Some structures and yarn combinations like a sett closer than a balanced sett, and some like a little more open sett. There are many aspects to sett, as your knowledge deepens so will your approach to setting your fabric in the rigid-heddle world. Here are a few blog posts that will help you think about selecting sett.
Open, Balanced, and Close Setts
Sett In a Multi Heddle World includes a discussion of Ashenhurst calculator
Take-Up and Shrinkage
Take-up is the amount the fabric will rebound once it is released from the loom. Shrinkage is how much the fabric will change once it is washed. The amount of take up and shrinkage, depends on the fibers used, yarn construction, and the weave structure. A general rule is to allow 10-15% for cotton, 15-20% for wool, and 25-30% for highly elastic yarns, but results vary and if being precise is important that swatching or sampling is a good idea.
Take-up and shrinkage rates can also be influenced by structure. Plain weave fabric or fabrics with plain weave between picks, for example Summer and Winter and overshot, take-up less than fabrics that don’t have plain weave picks such as twill and lace. In general, I calculate my take-up on the fiber content and if I know my structure will take up more I’ll use the upper end of the conventional range.
The total length you would like your project or projects to be, extra length, “loom waste”, to tie onto the front and back apron rods, and any extra length required between projects if you are making more than one project on the same warp.
When using the direct warping method 16″-18″ is an average amount of loom waste, when using the indirect method and about 22″-24″ is the average. The amount can vary depending on your loom, your project, and your warping style. Loom waste also includes any extra length you need between projects. Loom waste isn’t all “waste”, it can be used for fringe.
Number of Warp Ends
The total number of warp ends in your project. If you are using the direct warping method, keep in mind you are threading 2 ends at a time when threading the slots so you have to divide your total number of ends by two to determine how many slots you need to fill to get the correct number of ends. If you are using odd ended structures or colorwork the indirect number is recommended.
Adjusting for Structure or Color Repeats and Balances
A repeat is the fundamental element of your cloth. It could be the structure or color order or both. This element is repeated over and over again to your desired width and length. You can have more than one kind of repeat in your fabric.
A balance is a small portion of the repeat that creates either an even distribution of structural repeats across the width of your warp or the same interlacement at either selvedge. Balances are sometimes, but not always, needed to give the cloth structural integrity.
Once you have determined the number of ends it takes to weave your optimal width, divide it by your structure or color repeats to determine if they fit evenly into your width. To do this divide the number of ends it takes to complete one repeat into the number of ends.
You may need to add ends to complete a repeat or add a balance. Enter this number into the “end adjustments for repeats and balance” space.
Width in the Reed/Rigid Heddle
The total number of warp ends divided by your sett, will give you the woven width of your project with take-up and shrinkage estimations. Use this figure to center your project.
The total amount of yarn you will need to warp your loom.
You can be more precise with this calculation by estimating your picks per inch and multiply that figure by your width in the rigid-heddle reed, woven length, and take-up and shrinkage. I tend to cheat and just estimate a bit less yardage than my warp since no loom waste estimate is required for weft. The formula to figure out your exact yardage is width × sett × picks × length × take-up and shrinkages
Most patterns don’t give you this number, but I like to have a ballpark figure for how much extra I need to weave to get the final length I’m aiming for. If you are weaving one project on the warp, you can just weave until you can’t weave anymore. If you are weaving multiple projects, it may be helpful to make this calculation.