To get "straight" diagonal seams for joining binding....
lay one strip over the end of the other extending about 1/4" on end of each piece. Put needle in the "v" of upper left and sew to "v" of lower right. Putting the needle in the "v" is not into the fabric but is to line up the seam on the edge. Works every time to get good straight joinings. Look at my program on www.quilterstv.com on binding. There are two and will have to scroll thru to find both of them. The newer one addes to the original.