Richard Farlow sends a tip using a combination of two commands to create mitered edges in objects.
"The Interfere tool and the Slice tool are two separate 3D editing commands available in AutoCAD. The Interfere tool finds the area where two or more objects intersect, and creates a 3D object of that area. This gives you edges to work with when you proceed with the Slice command. Slice will cut an object into two pieces along a defined plane.
"For modeling compound miters to find miter or bevel angles, such as multisided planter boxes, first extrude the parts through each other. Then use the Interfere tool and retain the interference object it creates. Now you have vertices which are easy to osnap to in order to Slice using a three-point pick."
Notes from Cadalyst Tip Patrol: In this tip, Interfere creates an object that you can snap to when creating a cutting plane with Slice. Otherwise, you can't select intersection points of solid objects.