Sewing Set-in Seams: 9 Easy Steps For Adding Squares, Triangles, Or Diamonds For Quilting

Do you find yourself shying away from sewing diamonds and some triangles because you think that sewing the set-in seams (or Y seams) will be too difficult and your corners will be a mess?

The large squares between the star points were
sewn using the set-in seam technique shown below.

For many years in my quilting, I avoided anything that wasn’t a straight seam, even though there were quilts I really wanted to make.

Then there came a day when I saw a picture of a quilt I really wanted to make. Then the desire to tackle the set-in seams was greater than the will to avoid them.

With a little practice and some tips from a friend, I discovered that they really aren’t that difficult, they just take some time. If someone figures out a way to speed sew set-in seams, that person will become the hero of quilters everywhere.

Obviously, I haven’t figured a speedy way to piece these out yet, but I have mastered set in (or Y) seams, and my method is described below.

If you click on each picture, you will see a larger image so you can get a close look.

This is the square I will add between the points of two diamonds. 
Whether you are adding squares, triangles, or sewing diamonds, the process is the same. The first thing you need is to make sure that your stitching ends 1/4 inch away from the raw edge of the fabric where you will add the square or triangle. In the picture to the left, two diamonds have been sewn together and the seam ends 1/4 inch away from what would be the center of a star. Some quilters backstitch at the end because there will not be stitching that will cross over that seam. I generally do not, I just leave long tails on my threads.
Next, take the piece that you will be adding – in this case, I am adding a square – and line it up with your diamond. There should be a 1/4 inch on the square that extends beyond the seam that holds the diamonds together. In addition, the tip of your diamond should extend beyond the square (assuming you have not trimmed the tips of your diamonds).

Pin along the seam line. In this picture, you can see how the tip of the diamond extends beyond the square. I pin very carefully. I think the key to successful set-in seams is making sure that all of the individual patches line up and fit correctly.
Many quilters begin at the tip of the diamond to sew their set in seam. I have found that my accuracy increases when I start at the center and sew to the outside. I do understand that there is extra bulk at that seam that may be avoided if you start at the edge. However, because I can put my needle directly in the hole of the last stitch, I prefer to start in the center. I also like to sew have the diamond on the top – that way I can see where the other seam ends. By pinning carefully, the fabric is less likely to stretch, and the resulting patch is more likely to be flat.
This is what the center will look like after you have sewn one side of the square or triangle. You can see that I have left the threads a little longer than normal, and I have avoided the bulk of backstitching.
Now you are ready to attach the second side of your square. You will need to fold the diamonds in weird kinds of ways in order to make sure that your center sides line up. The corner of the square should like up with the second diamond (the one you will be attaching the square too). The tip of that diamond will extend beyond the end of your square, just as it did when you sewed the other side. Once you have pinned the square and diamond together, you are ready to sew.
When I add this site, I will have the square on the top.I can still see where the seam ends and I should place my needle to sew this side, but I won’t be distracted by other stitching. Because I have done careful pinning, I will be sure that the diamond and square will fit together correctly without stretching either.
Once your stitching has been finished, this is what the corner seam will look like – before you press it. You may notice the extra-long tails on the threads. I have not backstitched any of these seams. And they will be pressed with both sides folded facing in the same direction. Between the security of being folded inside the seam and any quilting that is done, I have had success in keeping these corners sewn together. The reason for backstitching is to make sure that the stitching doesn’t come out. 
This is what the seam looks like after it has been pressed. You will see that I press the seams facing toward the square (or triangle) that was added. In addition, the seam between the two diamonds is folded to one side. You may want to check out the article on sewing diamonds for star quilts to get more details. In that article, the seams between the diamonds are pressed open, which is an option. Whether you press your seams open or to one side as you sew your star, you will press the squares with the seam allowances facing toward the square (or triangle).

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