Abstract: A boring tool having a tool head rotatable about its axis and movable in direction of the axis along a working stroke and a return stroke. A knife having a pair of opposite cutting edges is floatingly mounted in a slot of the tool head extending transverse to the axis thereof and tiltable in the slot between a working position and a withdrawal position in which the cutting edges of the knife project a smaller distance beyond the periphery of the tool head than in the working position to prevent damage of the machined surface during the return stroke of the tool head.