In a core drilling apparatus to be equipped with a pilot drill in use,
- a mandrel body which is elongated and has opposed ends with one of said ends adapted to be rotatably coupled to a rotary drive means and a longitudinally extending externally threaded portion intermediate said distal ends and the other of said distal ends defining a driver surface and means for securing said pilot drill to said other end so that the pilot drill projects from said driver surface,
- a core drill body having an axis of rotation and opposed ends and a hole therethrough which is centered on the axis of rotation and opening at said opposing ends of the drill body, a first portion of the hole opening at one of said ends and having internal threads, and a second portion of the hole opening at the other of said ends of the drill body, a circular cutting edge provided at said other end about said other end opening, said second portion having a diameter which is radially enlarged relative to the first portion to enable the second portion of the hole to receive a core of work material cut by the cutting edge,
- the externally threaded portion of the mandrel body being threaded into the internally threaded first portion of the hole,
- latch means for providing a positive rotatable coupling between the bodies of the mandrel and the core drill for performing a cutting operation, and alternatively, releasing the positive rotatable coupling for permitting threaded movement of the mandrel body in the core drill body for ejection of the cut core from the hole, said latch means including a first and second abutment means each having a coupling surface extending along parallels to a plane coinciding with the longitudinal axis of the mandrel body, between points spaced apart from one another in the plane axially of the mandrel body, and an abutment surface extending in a plane transverse the longitudinal axis of the mandrel body at a point operatively offset from the coupling surface of the respective first or second abutment means axially of the mandrel body,
- means for rotatably coupling and axially fixing the first abutment means to one of the mandrel body and the core drill body,
- means mounting the second abutment means on the other of said mandrel body and said core drill body for axial movement on said other body between a first position in which the respective coupling surfaces and abutment surfaces of the first and second abutment means are aligned with one another and abutted with one another respectively, in planes coinciding with and transverse the axis of the mandrel body, respectively, and a second position in which the respective abutment surfaces of the first and second abutment means are operatively disengaged and spaced apart from one another axially of said other body, and
- means whereby the coupling surfaces of the first and second abutment means are interengageable with one another when the second abutment means are moved axially on said other body to the first position thereof, to positively couple the bodies of the mandrel and the core drill, and the respective first and second abutment means, for rotation in unison with one another about the longitudinal axis of the mandrel body for the cutting operation, and alternatively, disengageable from one another when the second abutment means are moved axially on said other body to the second position thereof, to permit the mandrel body to be threadedly moved in the core drill body for the ejection operation,
- the driver surface being recessed in the second portion of the hole, relative to said other end of the core drill body, when the second abutment means are in the first position thereof, and the length of said threaded portion and the distance between said first and second positions of the second abutment means being of sufficient lengths to enable the mandrel body to be threadedly moved in the core drill body to an ejection position in which the driver surface is substantially coplanar with a plane defined by said cutting edge when the second abutment means are moved axially on said other body to the second position thereof.