Patent ID: 7798751

Claim:
A method of drilling a hole in a workpiece, comprising: mounting a tubular inner housing within a bore of a tubular outer housing; mounting a motor assembly in the inner housing; providing an annular pneumatic cylinder between the inner housing and the outer housing; inserting a drill bit into a chuck of the motor assembly; supplying air pressure to the motor assembly to rotate the chuck and to the pneumatic cylinder to move the inner housing between the retracted and extended positions; providing forward and rearward sealed annular fluid restrictor chambers between the inner housing and the outer housing containing hydraulic fluid; providing a bypass passage between the forward and rearward chambers; while moving the inner housing forward, causing hydraulic fluid to flow from the forward chamber through the bypass passage to the rearward chamber to limit the speed of the movement to the extended position; and adjusting the flow rate of the hydraulic fluid through the bypass passage to select a desired speed.