Abstract: A square hole drill having a cutterhead configuration whose outline is in the form of a Reuleaux triangle and which also has a planetary gear drive. Two counter revolving motions are present in the drill at the same time. One is the pure rotary motion of the drill's cutterhead about its own shaft. The other is the circular motion of the cutterhead as a unit about a center line due to its eccentric mounting and drive. To achieve the opposite rotation of the unit as a whole compared to the rotation of the cutterhead about its own axis, a combined meshing planet gear and ring gear are used. The planet gear is directly connected to the cutterhead by a shaft rigidly attached to the gear's front side. At the rear side of the planet gear is the eccentrically mounted drive shaft. Surrounding the external teeth of the planet gear is a larger stationary ring gear with internal teeth to continuously engage the planet gear's teeth.