Ladies from my church knot comforter tops on Wednesday nights. I don't help with the knotting but I do donate comforter tops and help with binding.
We don't make separate binding for the comforters, we turn the backing fabric to the front then use that for binding. I was never pleased with my corners then I remembered a Eleanor Burns program from years ago. She showed how to self bind with mitered corners.
It took me awhile to remember how to do it. I'm going to share the process with you and this way it will be in writing so I can review it for myself.
After the top is knotted, you trim the batting to the edge of the top then cut the backing. You need to cut the backing twice the size of what you want to show on the top. If you want to show 1/2" binding, you cut the backing fabric at 1".
The backing fabric for this tutorial was trimmed at 1.5", the binding that shows on the top of the comforter will be 3/4".
On the inside of each corner, mark 3/4" lines and 1.5" lines. (Whatever size you want your binding to be, the outside lines are half the size of what the backing is trimmed to.) You've made a square inside of these lines.
Eleanor recommends folding the fabric over and pressing the 3/4" line which is a good idea. I don't do that because the batting in these comforters is polyester. Polyester and a hot iron don't mix well together for me.
Lay a ruler so a line intersects the intersections of the square and mark a line on top of the ruler.
Make sure the lines goes through the 3/4" lines on both sides.
Fold the corner so it makes a triangle and pin like shown.
Stitch the line starting at the 3/4" line, make sure you back stitch.