Binding for 60 Degree Corners, from Harriet Hargrave & Carrie Hargrave’s Quilter’s Academy Vol. 4 – Senior Year, p. 124-125.
If you have trimmed the sides of a hexagon quilt to straight edges, you may still encounter 60 degree corners. These are handled in the same manner as a square corner, but the turn is not a true miter. The process is the same but with a small adjustment.
If you are binding many inside and outside corners, be patient. There is a lot of turning and mitering involved.
Start the process by sewing a line of stitching, just a thread narrower than your seam allowance, around all the edges of the quilt. Make a small clip straight from the edge to the inside point, stopping just shy of the stitching. This will allow you to straighten the edge as you apply the binding.
You will find that binding a complex edge like this is easier with narrow binding.
Start sewing the binding onto the edge. Be sure to leave about 8″-10″ at the beginning and start sewing on an outside straight edge, if possible. Sew toward the first inside point and stop with your needle in the down position, using a seam allowance slightly wider than 1/8″.
With the needle still in the fabric, lift the presser foot and pull the edge straight behind the needle so that you create a straight edge. If you have a knee lift for your presser foot, this is the perfect place to use it. The clip that you made will allow the edge to straighten. Continue sewing. Notice that there is no miter here and the binding is standing straight up. The miter will be formed when you hand stitch the binding into place.
Once you get to the outside corner, stop stitching at the seamline, turn the quilt, and backstitch off the edge, making sure you stay at the same angle as the raw edge on the right. You will not be stitching straight but at the 60 degree angle. Pull the quilt away from the needle and fold the binding up. Fold the binding over itself at the corner and align the raw edge of the binding and the edge of the quilt. This is exactly how you miter a square corner – but unlike a square corner, where all the edges align with one another, this time the binding will not align with the top edge of the quilt.
Once you have been around all sides of the quilt, join the ends. Trim all the layers if necessary to keep the seam allowance exactly the same width. Turn the binding to the back, fold over the seam allowance, and align the folded edge with the seam. Hand stitch, suing either a blind or a ladder stitch.