drill feed and retraction mechanism 36 this action initiates the feeding and drilling movement of the drill 39 s spindle and associated chuck 20 and cutter 22 the drilling operation continues at a normal cycle by positively advancing the rotating cutter 22 until the desired depth has been reached at which point the drill mechanism retracts the spindle at the end of the drill stroke cycle shifting sleeve 24 is displaced downward and back upward as described above a counter assembly 40 is mounted to the drill housing on a housing segment 42 above shifting sleeve 24 counter 40 is a numerical digital air pulse counting device adapted to count down from a preset number to zero and then open an internal valve providing communication between an inlet and an outlet thereof counter 40 is provided with a face cover 44 mounted over a dial portion and a manual reset button 46 counter face cover 44 is removably mounted on the counter by fasteners to protect the counter dial and prevent unauthorized tampering with the counter 39 s numerical setting or the reset button 46 counter 40 is connected by a conduit 48 to air source 30 a count valve 50 is a normally open valve having an inlet connected by conduit 52 to air supply conduit 48 and having an outlet connected.