An attachment for clamping a portable drill to a work piece includes a foot member which positions a portable drill with respect to a work piece. A contact pad applies pressure to the surface of the work piece. Located between the contact pad and the means for engagement of the portable drill is a guide path in which a housing is slidably mounted. Affixed to the housing is a means for applying a vertical force and a collet member. Said means being anti-back drivable. The vertical force is applied to a mandrel so that the mandrel expands the collet. Once the collet has been expanded, a force is placed on the contact pad and on the means for engaging the portable drill. Consequently, the portable drill is held in place at the desired location for drilling a finish hole using minimal force.