Unfortunately I’ve seen this in most major brands of miter saws. You can square the blade in fixed position, but then the sliding action is off about 1/16”. I can get the sliding action to cut square to the fence, but then the fixed cutting is off by the 1/16”. My research tells me the machining process is off somewhere. I believe the rails aren’t machined parallel to the blade. It’s very frustrating! Dewalt seems to be the only company that can get all the parts machined properly so the components are square and parallel.
