The prior art drilling apparatus utilizes augers which may include a lead or pilot bit for starting the hole in the earth, reamers for boring the hole to the desired diameter, and fluted or spiral screw flight augers for removal of earth through the top of the hole.
Various problems exist with the prior art drilling apparatus. For example, when drilling through frozen earth or rock the pilot portion, which may have been welded, soldered or riveted to the reamer, often broke off. Also, when the cutting edge of the pilot or reamer became blunt or dull from use it was necessary to replace the entire apparatus. In addition, sharpening the prior art earth drilling implements resulted in corresponding undesired decreases in the diameter of the hole being bored. Finally, the prior art drills were capable of boring a hole of a single diameter; to bore holes of different diameters a new pilot, reamer and auger unit were required.