Y-Seams

Y-Seams are where three seams come together to form a Y. The most common place on a quilt where you will do Y-Seams is when you want to miter the corners of a quilt border, but they can also sometimes be found inside quilt blocks, too. Often two of the seams come together at a 90° angle and the third seam sticks out from the point of those seams at a 135° from each of the first two seams, but it is possible for the seams to be at any angles from each other, for instance, they could all be at 120° from each other. Regardless of the angles these seams are from each other, the technique for doing Y-Seams is the same.

Math and Cutting Instructions:

• Designate one piece as the Base Piece, often a piece with a 90° corner, like a square or the main body of your quilt top, or sometimes a Hexagon with a 120º corner.
• You will also need two strips to sew onto the Base Piece, like whatever you have chosen for your border.
  • These two strips need to have the same width as each other.
  • The length of the strips need to be the length of the base piece + (the width of the adjacent strip × the number of Y-Seams you are making with this particular strip).
    • Example 1: The base piece is 6½" square. You are framing it with 3½" border strips with miters (Y-Seams) at all four corners.
      • Each border strip will be involved in two miters (Y-Seams) each.
      • The length needs to be: 6½" + (3½" ×2) = 6½" + 7" = 13½"
    • Example 2: The base piece is a hexagon whose sides are each 3½" long. (All of these angles are 120°). We are adding a 3½" strip to two adjacent sides to create some artistic 3D-type shading.
      • Each strip will only be involved in one Y-Seam each.
      • The length needs to be 3½" + (3½" × 1) = 3½" + 3½" = 7"

Note: if your base unit is a hexagon, at least one of the sides you will be sewing a strip onto will be an unsupported bias edge. If you want to support this edge so that it doesn't stretch, I suggest ironing in a spray starch or starch alternative like Best Press™.

Sewing Instructions:

1. Prepare the base piece
   1. Turn your base piece wrong side up.
   2. Find the corner where you will be making the Y-Seam.
   3. Make a mark ¼" from each edge at this corner, forming an X.
   4. If you will be making Y-Seams at more than one corner of the base unit, make similar marks at each appropriate corner.
2. Prepare the strips that will be sewn onto the base
   1. Mark the back of each strip a distance from the end of the strip that is equal to the width of the strip.
      1. Example, the strips are 3½" wide
      2. Measure 3½" down the length of each strip and make a mark at this point.
3. Place the first strip along the edge of the base unit, right sides together, aligning the mark on the back of the strip with the corner of the base unit.
4. Sew the first strip to the base unit, with the base unit on the top as you sew.
   1. Do NOT start at the edge of the base unit.
   2. Start at the X you made in Step 1, sew four or five stitches forward, stop, sew backwards back to the X, then sew forward to complete the seam. This will lock the seam to keep it from coming unraveled, as the other two seams will NOT cross this seam.
   3. If this strip will be involved in another Y-Seam at the other end, stop at the X at the other end of the seam, sew backwards four or five stitches, then sew forward again, and stop again at the X.
5. Fold the end of the first strip back on itself and away from the corner of the base unit. You do not want it to get caught in the stitching when you sew the second strip onto the base unit.
6. Place the second strip along the edge of the base unit, right sides together, aligning the mark on the back of the strip with the corner of the base unit, in a similar way to what you did with the first strip.
7. Sew the second strip to the base unit, with the base unit on the top as you sew, being careful that you don't catch the first strip in this seam.
   1. Once again, do NOT start at the edge of the base unit.
   2. Start at the X, again locking the end of the seam with a section of backstitching, the same way you did with the first strip.
   3. If the other end of this second strip is also involved in another Y-Seam, also stop at the second X and lock the seam with another section of backstitching.
8. Fold the base unit in half through the corner where you are making the Y-Seam, right sides together and pin it out of the way of the strips. Line up the outer edges of the two strips, right sides together. You do not want the base unit getting caught in the next seam.
   1. For a square or rectangle base unit, it will be folded to look like a triangle.
   2. For a hexagonal base unit, it will be folded to look like a trapezoid.
9. Draw a line to mark the next seam line.
   1. If the base unit has a 90º angle, then draw the line starting from where the first 2 seams end, toward the outer edge of the loose ends of the strips at a 45º angle.
   2. If the base unit has a 120º angle, then draw the line starting from where the first 2 seams end, toward the outer edge and loose ends of the strips at a 30º angle, as measured from the outer edge of the strip.
   3. No matter what the angle, the drawn line should extend as a straight line from the fold of the base unit.
10. Sew the two strips together, being careful to NOT catch the base unit in this seam.
    1. Start at the point where the first seams end, and lock this seam with a section of backstitching, the same way you locked the first two seams.
    2. Sew on the line to the edge of the strips.
11. Carefully trim off the excess fabric from the seam allowance of the strips, cutting ¼" away from the seam, and being careful to not cut the base unit.
12. Unfold the unit. You should now have three seams meeting together at one point, forming a Y.
13. Press the first two seams towards the strips and press the third seam to one side.
14. To form diamonds from the strips attached to the hexagon, now trim the other end of the strips to line up with the edges of the hexagon.

Note: Some quilt designers will have you trim your strips on the diagonal before you sew them onto the base unit. The technique for sewing the three seams is the same, just be careful that you don't stretch the unsupported bias edges.