A portable, air powered drill has an automated feed system and an adjustable dwell for producing countersunk holes in a workpiece. The feed system uses hydraulic cylinders and pneumatic control logic to control the feed rate, and the dwell time of a countersink drill bit at the end of the drill stroke. A movable mechanical stop permits an operator user to adjust countersink depth. The control logic provides fully automatic feed of the drill bit, and adjustment of the dwell time to consistently produce identical countersunk holes in a variety of workpiece materials.