Okay, sounds crazy, but I sew mine together like a nine patch and then cut like a D9P. To do this, 1 determine width of sashing, multipy by 2, + 1" for seams. Then cut to length of block side. Use contrasting square in center of this ...it will become the corner stones. After sewing all together, I cut same as I do when making a D9P. You do have to be careful if your block hss a definate top and bottom or left to rt orientation and place in the nine patch accordingly. I get near perfect sashing and cornerstones every time.