Hydraulically controlled drill unit

Claim 1

A drill unit adapted for controlled axial movement of a drill from a retracted position toward a workpiece, comprising a housing, a quill mounted within said housing and axially movable with respect thereto, a spindle rotatably mounted in said quill and axially fixed with respect thereto, said spindle having means at its outer end to receive the shank of a drill, means for rotating said spindle, piston means fixed to said quill defining a first chamber and a second chamber on either side of said piston means between said housing and said quill, said second chamber being disposed between said piston means and the workpiece, a cylinder having a piston disposed therein dividing said cylinder into a third chamber and a fourth chamber, said second chamber and said third chamber being in fluid communication and containing a substantially non-compressible fluid, means for controlled admission of compressed gas to said first chamber whereby said piston means and said quill are urged toward the workpiece, large capacity flow control means disposed between said second chamber and said third chamber adapted to permit rapid flow of the substantially non-compressible fluid from said second chamber to said third chamber to thereby permit rapid advancement of said quill and said spindle toward the workpiece, control means responsive to the axial position of said quill and said spindle adapted to close said large capacity flow control means when the drill reaches a preselected position adjacent the workpiece, and small capacity flow control means disposed between said second chamber and said third chamber adapted to permit flow of the substantially non-compressible fluid from said second chamber to said third chamber at a preselected controlled slow rate relative to said large capacity flow control means to thereby permit the drill to be fed into the workpiece at a controlled rate.