This is taken from my new book, Weaving for Beginners, on page 280. The information is also found in my Book #1, Winding a Warp and Using a Paddle. See the chapters devoted to sett (epi).
Make your weaving easier: Use the 80% number
(Ashenhurst’s percentage)
In industry, a balanced looking fabric is actually a bit more warp predominant than precisely balanced. It looks balanced at a glance, but upon inspection, you will see that there are more warps per inch than wefts per inch. We handweavers can use this principle, too. I almost always do when I want a generally balanced weave. The way to achieve this look is to take 80% of the maximum sett using the Ashenhurst calculation.
(More on the percentages on pages 280 (Beginner’s Book) and 93 (Book #1).
Why it’s so wonderful to weave with a slightly closer warp sett:
1. The edges of the cloth (selvedges) don’t draw in as much, so the selvedges
don’t break. The extra warps instead of 50-50 hold out the warp width.
2. You don’t have to make sure the weft is put in very loosely. The natural
diagonal the shuttle makes when you throw it through, from the last row of
weaving to the beater, is usually enough slack for the weft’s pathway. (If the
weft is put in without any diagonal, it will pull in the edges of your cloth.)
3. There is less trouble with warp breakage. Fragile warp threads can be used
because there are more of them to pull their weight on the job.
4. There are fewer wefts (picks) per inch so the weaving goes faster.
Now, don’t those reasons sound enticing?
In general, whenever I’m debating between two numbers for a sett, I’ll choose
the denser number for the above reasons. That means, if I were debating
between 6 and 8‑epi, I’d tend to choose the higher number of 8. If I’m weaving
an open shawl, however, I want it more open than the 80% number, for sure.
Of course, my sample will be the ultimate test. Read on for when not to use the
80% number.