Setting the Seam...Why?
 

Since day one, I have always read, watched, or been told to set my seam with the iron (give it a good pressing) before pressing the seam to one side, or open. When I asked why, I've always gotten some cryptic answer in, mystic, "quiltese." I'm baffled. Would someone please give me a more scientific reason to "set my seam." Thanks.

Setting the seam from the back, then pressing it to one side from the front accomplishes two things that I've experienced: 1) It seems to "nestle" the thread into the layers of fabrics, and 2) The seam is now warmed and very pliable to send that seam to one side or the other when ironing from the right side . . . no overlaps or little tucks at the seam.

You'll find that your measurements stay very true as well.

Hope this helps.

I also think it makes the block lie flatter

I think it matters only when accuracy is really important for a quilt top. Many of the tops I make are the fast and easy type where absolute accuracy has little to do with outcome -- patterns such as "Falling Charms" from the Missouri Quilt Company, for example. Fast and furious works fine for those types of patterns where you don't have to match triangles to squares, etc.

I think it always looks nicer when setting the seams. The seams also line up better.

It is one of those things that you do, not really sure why, but the seams do lay nicely.

You know how sometimes you run your fingernail down a seam to ease the sense of 'gathering' or along a fold of a piece of paper because it makes it "sharper"? That's why I "set the seam" before pressing the block/strip open. Just makes it look a bit neater and easier to abut the seams when joining to another section or clock. :)

Jan in VA

You can try this. Sew 2 patches together, now just unsew them by clipping the stitches from one side or the other. Should be pretty easy to grab the stitches with your seam ripper. Now sew them together again, and this time set the seam. If you try and unpick the seam it will be more difficult because the thread has embedded itself into the fabric a bit.

I quit setting seams. I have made several hundred square in a square blocks. The second and fourth triangle added just never laid as flat as the first and the third. I never could figure out why. Then one time I just put the first triangles on and pressed them open before I put the second triangle on. That time the second triangles laid as flat as the first ones. The difference is the first ones didn't get set and because the second triangles were already on and got set when I pressed the first ones open.