Then he set up an arrangement like this to actually cut the miters. The sacrificial pieces give a edge to run along a temporary fence. They also become built in clamping points to glue up the miter. I also put a chamfer on the other 3 edges of the part that drapes down before I glued it up. I put in a couple of biscuits to help with alignment. After the glue up, I chiseled most of the sacrificial pieces off, and cleaned the rest of it with a plane. I didn't take very long to do, and it really gave a nice joint doing it this way