An abrasive rotary tool includes a tool shank defining an axis of rotation for the rotary tool, and an abrasive external working surface. The abrasive external working surface includes a resin, and a plurality of porous ceramic abrasive composites dispersed in the resin, the porous ceramic abrasive composites including individual abrasive particles dispersed in a porous ceramic matrix. At least a portion of the porous ceramic matrix comprises glassy ceramic material. A ratio of the average porous ceramic abrasive composite size to the average individual abrasive particle size is no greater than 15 to 1.

An abrasive rotary tool includes a tool shank a flexible planar section positioned opposite the tool shank. The flexible planar section forms a first abrasive external surface on a first side of the flexible planar section and a second abrasive external surface on a second side of the flexible planar section. The flexible planar section facilitates abrading, corners of a workpiece across multiple angles relative to the axis of rotation for the rotary tool through bending of the flexible planar section when the abrasive external surfaces are applied to a corner of the workpiece.

An abrasive rotary tool includes a tool shank a flexible planar section positioned opposite the tool shank. The flexible planar section forms a first abrasive external surface on a first side of the flexible planar section and a second abrasive external surface on a second side of the flexible planar section. The flexible planar section facilitates abrading, corners of a workpiece across multiple angles relative to the axis of rotation for the rotary tool through bending of the flexible planar section when the abrasive external surfaces are applied to a corner of the workpiece.

A diameter expansion drill bit used for inserting in a prepared hole perforated in a framework to expand a diameter of a portion of the prepared hole by grinding has a plurality of blade sections that grind the portion of the prepared hole, a blade holding section that holds the plurality of blade sections movably in a radial direction respectively, and a shank section that supports the blade holding section, and the plurality of blade sections move to spread outwardly in the radial direction with respect to the blade holding section by centrifugal force due to rotation.

A diameter expansion drill bit used for inserting in a prepared hole perforated in a framework to expand a diameter of a portion of the prepared hole by grinding has a plurality of blade sections that grind the portion of the prepared hole, a blade holding section that holds the plurality of blade sections movably in a radial direction respectively, and a shank section that supports the blade holding section, and the plurality of blade sections move to spread outwardly in the radial direction with respect to the blade holding section by centrifugal force due to rotation.