Drill bit carrier with replaceable cutting edges also includes improved pilot drill for accuracy

摘要

The drill bit (1) carrier is tipped with interchangeable cutters (2) and includes a central bore (3) for a pilot drill. This is held and guided by its cylindrical shank (4) and has cutting edges (6) and swarf clearing grooves (7) of the spiral drill type. The innovative feature is the provision of a polygonal cross-section at the end (8) of the pilot drill shank, gripped in a matching polygonal recess in the end of the central bore (3) of the main carrier. The end (8) of the shank (4) is pentagonal (9), and over almost its entire length, has a chordal-, i.e. D-section, -flattening, (11), which is the extension of one surface of the polygon. The pilot drill (5) is secured in the central bore (3) by a screw (12) pressing against the flat (11). The end of the pilot drill shank is supported against an axially adjustable setscrew (14). The shank has a smaller diameter than the remaining pilot drill section, producing a corresponding shoulder (15).