Abstract: An apparatus for creating annular cavities in the bottom of drilled holes in any medium having a body, an axle within the body at one end and rotated by a conventional drill, a reamer secured to the axle at its other end, an inner part enveloping the axle and an outer part enveloping the inner part, both parts being eccentric and rotatable with respect to each other. Their respective eccentricities are such that when opposing each other in opposite directions, the axle is parallel to the outer part. Joint rotation of the parts causes the reamer to move in a planetary manner. The outer part may be held stationary or dragged along by the inner part for joint rotation. Channels are provided within the parts to the reamer to supply cooling water to the reamer and to remove waste material generated by the reamer.