Abstract: A positive feed drill assembly having an air powered motor and an automatic drill feed and retract mechanism with a normal feed, drill, and retract sequence of operation is provided with an improvement to control the number of times the drill can be used to make a hole with a particular cutter. The improvement includes an apparatus associated with the automatic feed and retract mechanism for sensing the cycle of each drilling operation. A counter functioning with the sensing apparatus counts the number of drilling operations. A comparator associated with the counter compares the accumulated number of drilling operations with a predetermined number. A signaling apparatus connected with the counter provides a signal to the operator when the drill assembly has performed the maximum number of drilling operations for that cutter so the operator can replace the cutter before using the drill assembly again.

Abstract: The improved locking means includes a pair of shaft mounted gears that are in mesh with the thread on the exterior of the feed screw mounted in the housing of a positive feed drill. On the opposite ends of the shafts are mounted gears which rotate with the shafts. When the drill tool holder is not to be advanced, the gears and shafts rotate as the feed screw is being rotated and thus do not cause axial movement of the feed screw as the feed screw rotates. A rack gear is located in the housing adjacent the spur gears. A pressure actuated piston is provided to move the rack gear into engagement with the spur gears to lock the spur gears and shafts against rotation. When this occurs, the gears in mesh with the thread on the feed screw act as a fulcrum so that the feed screw and tool holder are moved axially as the feed screw rotates.