A machine for boring a shaft in earth strata or the like. An annular support ring means having an outside diameter approxiately equal to the diameter of the shaft which is selectively engageable or disengageable with the shaft wall by the use of clamping means is disclosed. A carriage means which is slidably mounted on the annular support ring means and orbital thereabout is also disclosed. A rotary cutting wheel means having a diameter substantially smaller than the diameter of the shaft is mounted on the carriage means and is axially displaceable with respect thereto for movement in a direction which may be parallel or inclined with respect to the axis of the shaft. Various drive means for moving the carriage means circumferentially about the annular support ring means, and for moving the rotary cutting wheel means in an axial direction with respect to the carriage means, and for rotating the rotary cutting wheel means are described. The use of the machine to make an overlapping helical path cut in earth strata whereby a generally cylindrical shaft is created is also described.