Monday, May 26, 2008

Calculating Sett

By Leigh

When it comes to calculating sett, I am a great fan of using charts. My favorite sett charts are found in the appendix of Peggy Osterkamp's New Guide to Weaving Volume 1: Winding a Warp and Using a Paddle. (You can see samples of these charts at her website, here.) Usually I can find what I need on one of these charts, however, I do have some oddball yarns that I've picked up here and there, which sometimes aren't listed.

Such is the case with the 16/3 cotton I want to use for my next multiple tabby weave experiment. So far, I've mostly used 8/2s cottons, because that's what I have a lot of. But I want to weave some everyday table napkins in navy and white, and I need a lighter weight warp yarn to go with the heavier navy weft.

Peggy's charts don't list 16/3 cotton, so I'm going to have to resort to another method to calculate the sett. I've decided to try something new, so here I am, thinking "out loud." Trying to explain concepts to others always helps clarify them for me. I only hope that in the end, all of this makes sense to you too!

The first step for any method is to figure out the wraps per inch.

Wraps per inch (WPI) can be calculated in one of two ways. The first way is to physically wrap the yarn around a one inch measure and to count how many wraps it takes to achieve a solid inch of yarn. A more detailed description of how to do this is here.

The second way is by using the Ashenhurst Rule.

The Ashenhurst Rule calculates the wraps per inch without doing the wrapping. This is especially helpful for fine or slippery yarns. This method is found in Winding a Warp and Using a Paddle, on page 90. If you don't have that book and would like to read a more detailed explanation, you can find the excerpt here.

Here's the formula:

WPI = 0.9 x √ of YPP

WPI = wraps (diameters) per inch
√ = square root of
YPP = yards per pound

The key to this one is knowing the yards per pound of the yarn. Sometimes this information is readily available, sometimes not. In my case I have absolutely no idea. However, I can figure it out with a McMorran Balance.

I considered doing a tutorial on how to use the McMorran Balance, but Laritza at Yorksett Arts & Crafts already has a good one, so I will refer you to it; just click here.

Using my McMorran Balance, I discover that the ypp is 5250. Grabbing my calculator and plugging that number into the formula, I get:

0.9 x √ of 5250 = 65.25 WPI.

Okay. So 65 and a quarter wraps will give me a solidly covered inch of my yarn. However, I need to make room for the weft, so that requires another calculation (this version also from Osterkamp):

Sett = WPI x weave firmness

This is how I learned to calculate sett.

WPI ÷ 2 = epi for balanced plain weave
WPI x 2/3 = epi for balanced 2/2 twill

Where WPI = wraps per inch and
..............epi = ends per inch

This gives what Peggy calls "maximum sett" for a balanced weave. If the sett is closer, then the fabric becomes warp dominant. One the other hand, the weaver may want a softer fabric. We have two choices here too. One can either weave a bunch of samples to decide what is best, or one can try ....

Allowing for the Purpose

This is something else found in Peggy's book. She lists suggested percentages to use depending upon the weave firmness wanted. This is based on the purpose for which the cloth will be used. You can find the box chart on page 93 of her book, or read the excerpt online here.

The threading draft I am planning to use is a broken twill, and my yarn is 65.25 WPI, so here are my calculations:

65 WPI x 2/3 (or .67 on my calculator) = 43 epi maximum sett

Taking Peggy's recommendation for 80% of maximum sett, (see "Sett: Making Your Weaving Easier").

43 x .8 = 34 epi to start.

So there you have it. The art and science of calculating sett. The science is in the math, and the art is in the weaver's choices based on knowledge and experience.

There are a couple of other methods, but these are the only ones I have experience with so far. I'd love to hear your thoughts and experiences, so please leave a comment if you feel so inclined.

Posted 26 May 2008 at http://leighsfiberjournal.blogspot.com

Related posts:
Another Way to Calculate Sett
Measuring Wraps Per Inch (WPI)
How to Use a McMorran Balance (Yorksett Arts & Crafts)

15 comments:

  1. Peggy Osterkamp's book is another one on my wish list! And, at the risk of sounding greedy, I'd also like a McMorran balance.... For now I use the actual wrapping method around a little inch gauge or - for a fine yarn - a cm gauge: a little wooden rectangle with a piece cut out of the appropriate length.

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  2. Wow, so much to learn from in this post - thankyou!

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  3. Hi Leigh,

    I think that part of Osterkamp's book alone is worth the price of the book. Two things. One, it is probably impossible to weave a balanced weave sett at half the wpi. Think about how warp and weft cross each other: there is some up and down in the crossing as well as side to side. That is why the maximum sett is 90% and that is for upholstery and that is really really stiff! Second, if you look on p. 91 she tells you another way to calculate ypp by using official standards. The full table of standards is on p. 113.

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  4. Peg, I was hoping you'd comment on this as I know you use this method. There was a lot more I wanted to include, but the post was long enough as it is! Thanks for adding some of that info.

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  5. Great information. Thanks for taking the time to put it all in writing.

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  6. Mixture of art and math here. The math side is pretty concrete. The art side, is my right brain looking at the fiber itself, what weave structure(s) I'm working with, the kind of drape I want, and what the end purpose of the piece is going to be -- so often, I wind up using the math as the basis, then the art as a way to "feel" what I just know from experience is going to work a bit better or what direction I want to experiment in.

    All of Ms. Osterkamp's books are so good! What a wealth of information.

    And what a great blog post, Leigh. This one is a bookmark for sure.

    Weave on!
    Jane

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  7. Well put, Jane! It seems to me that the "art" side of fiber and textile arts often do get expressed as feelings. But I'm realizing that even those are based on experience. Hopefully, the more I weave, the more natural the whole process will become.

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  8. Hey Leigh, there's a Meme going around these days and I've been tagged, so in turn have tagged you. Go to my blog for instructions. We've exchanged emails from time to time and I look forward to learning more about you~

    p.s. This sett instruction is teriffic- thanks!!

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  9. Perfect timing! I had just taken out my sett calculations for my next project and was mulling them over a final time. The percentages system is new information for me! I've been expecting to have to use some trial and error for this project as there are a lot of extra factors in it, but so far I have been using Sharon Alderman's formula in Mastering Weave Structures:

    sett = wpi x R divided by (T+R )

    where R is thenumber of ends in one pattern repeat, and T is the number of intersections in one pattern repeat.

    She has some diagrams to help readers understand how to count intersections (i.e. each time the weft passes from the one plane of the cloth to the other). Unfortunately hese can be a little confusing because her 3rd diagram (for 1/3 twill) has an error in it. You can download the corrections (errata) for the book at the Interweave Press site, although I'm not sure whether they caught this particular one.

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  10. whoops, that was unclear in my last comment. Sett=

    wpi x R
    ------
    (T + R)

    I used different letters for the variables than Sharon Alderman did, but you get the idea.

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  11. Trapunto, thank you for sharing this. Sharon Alderman's is one that I haven't tried. Her book is on my "must get" list, though I was hoping to wait until a second edition with the errata corrected!

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  12. Great Info, Leigh. Thank you.

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  13. Thanks for this! I have some silks from Habu that I have been wondering how I am going to find a sett for (as in 80 to 120 epi.)

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  14. I am belatedly thanking you for helping me figure out something that has been plaguing me for the past day!!! I have a weird yarn that I'm designing with, and I couldn't figure out how to sett it. Thanks to you, I'll finally be able to!

    (I can never get the actual wraps per inch to be consistent, so I've distrusted that method for a while. Now I can just use my calculator!)

    Thank you!

    Sue

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