Abstract: A piston mounted in a tool body is perpendicularly movable relative to the tool's longitudinal axis. A tool bit mounted on the piston protrudes perpendicularly away from the tool's body, relative to the longitudinal axis. A coupler rotatably and drivingly couples the tool to a line boring machine. The machine is operated to rotate and longitudinally move the tool along the longitudinal axis into a work piece bore, to position the rotating tool bit's cutting tip adjacent a selected internal circumferential portion of the work piece. Pressurized hydraulic fluid is then controllably applied to the piston, through the tool, to perpendicularly outwardly advance the piston relative to the longitudinal axis, forcing the rotating cutting tip into the work piece to cut a snap-ring groove. A spring mounted between the body and the piston biases the piston toward the longitudinal axis, retracting the tool bit when the fluid pressure is relieved.