A hand-held pneumatic-hydraulic drill unit employs modular drilling and clamp-up assemblies to perform a complete drilling cycle. The drilling cycle consists of: (1) clamping the drill unit to a work piece and/or a template that positions the drill unit relative to the workpiece; (2) advancing a rotating tool bit to perform the desired machining operation; (3) withdrawing the tool bit from the machined opening; and (4) releasing the clamping mechanism that secures the drill unit to the workpiece. The drill unit includes a pneumatic motor subassembly that is advanced toward and retracted from a workpiece by a hydraulically actuated feed cylinder. The motor subassembly and feed cylinder are axially aligned with one another. The clamp-up assembly of the drill unit also includes a clamp cylinder that is activated solely by hydraulic pressure. A modular, pneumatically actuated hydraulic pump is mounted on the drill unit and supplies pressurized hydraulic fluid to the feed and clamp cylinders. Variations in drilling depths, drilling speeds, feed rates, drilling thrusts, and clamp-up forces can be effected by changing modular components of the drill unit.