An automatic tool for machining interior surfaces of stationary work. A hollow shaft is rotated and moved axially, and a cutting member carried on a radial slide on one end of the shaft is moved by a push rod through an axial to radial motion transmitting device to vary the diameter of the bore. Axial movements of the push rod and shaft are delivered by input cylinders, the piston of which are connected to output sensing pistons which operate slave piston drive slides, indicating motion along two axes.