As a new quilter and clumsy in my old age, I am not good with the bias edges. I just did it the old fashioned way using 7 1/2 inch blocks, sewing corner to corner and squaring up to a 13 1/2 inch block after sewing the hourglass. I cut the block at 4 1/2 inches and ended up with a 12 1/2 inch block after squaring up just a wee bit from the edges, being careful to keep the corners as even as possible so they would match up. It is working for me so if you don't like bias edges, there is an alternative which most of you I'm sure are already aware.