I once thought of patenting this thing, instead, I leave it to you to post it if you wish. It’s also an expose’ on making tools out of concrete! This miter jig consists of concrete with polypropylene fibers for added strength. It describes a perfect 45 angle and the ‘table’ (piece of Corian on top) is at a dead 90 to the work. This, as seen, can even be used with material that is not flat. The work is clamped via cams. One routers the first pass on top of tape, feeding the router in a way as to prevent tear out. A second pass is done freehand with the tape removed. The idea is to not blow through the perimeter. This needs to only be done to one of the meeting miter surfaces. With a second router (plunge) on a sled, and without moving the work, a spline slot is cut. This ensures that the two miters line up perfectly.