Abstract: Apparatus for cutting a chamfer on an upper edge of a concrete slab includes a hub designed for installation on the threaded output spindle of an angle grinder, and a specially-modified diamond-grit-edged rotary blade which mounts on the hub. For a preferred embodiment of the hub, an attachment collar is unitary and concentric with both a blade mounting flange having countersunk blade-attachment screw holes and a blade centering shoulder on the flange. The attachment collar has at least one pair of flattened parallel sides for receiving a wrench used to tighten the hub on the output spindle. The blade which is equipped with both countersunk attachment holes and a central positioning aperture sized to fit closely over the blade centering shoulder, is attachable with countersinking screws to the mounting flange so that the head of each screw is flush with the surface of the blade.