Circular drill with centering device

In a cutting head assembly of the type adapted to be rotatably driven about its longitudinal axis and comprising a circular cutting head having a body portion with a plurality of cutting teeth circumferentially disposed with respect to its lower open end, the improvement comprising:

• A. a centering drill inwardly and concentrically positioned within said body portion such that an inner cutting head extends axially outwardly beyond the cutting teeth of said circular cutting head, said centering drill being:
• i) registrable at its periphery with the body portion of said outer circular drill in an initial cutting mode and
• ii) axially depressable within said body portion of said circular cutting head into a mode of non-registry with said body portions of said cutting head as a centering hole is cut, such that said centering drill ceases to rotate as said circular drill engages a surface to be cut, and
• B. a centering drill and coolant plug supporting in its periphery a liquid sealing means engageable with the inner wall of said body portion of said circular cutting head and supporting in its lower mid-portion said centering drill, said body portion including a lubricating channel extending into the body portion and openable so as to flow lubricant, as said centering drill is depressed to its mode of non-registry said centering drill and coolant plug including a plurality of ball detents embedded in its periphery and outwardly extending into complementary registering slots defined in the inner wall of said body portion so as to index said centering drill ad coolant plug with the body portion of said circular cutting head in said initial cutting mode.