Sometimes we need to add y-seams when creating a block. This often occurs when adding diamond shaped pieces or simply when we do not want to divide a shape into sections. Here's how to do it...
Step 1: Clip back any stitching within the seam allowance of the inset section. Do no clip beyond the corner point. If a seam already meets at this point, press it open.
Step 2: On wrong side of section to be added, draw in seam line, marking corner point.
Step 3: With right sides of sections together, place a pin through corner points of both sections and match the seam lines together exactly.
Step 4: Position sections under sewing machine and drop the needle into the exact position of the pin. Remove pin and sew first side of the section.
Step 5: Remove from machine. Turn pieces upside down so inset corner is on top and position work under needle again. Place needle into fabric through same point where last seam started. Twist remaining seam lines together so raw edges are even. Sew down second side.
Here's how the finished set in seam of eight-pointed star block looks.