What you need is a Jody Barrows Square in a Square ruler. It allows you to sew a straight piece of fabric on each side of your block. You then use the rules to cut off the excess at the right angle. It saves making triangles that stretch and is the easiest way I have found to do it. The quilt currently on my bed was made with that ruler. Check with your local QS they may offer a class if they sell the ruler. There may be a web site. Our local guild had a woman who teaches it demo it for us. It has been around since 1995.