Rotary drilling apparatus

摘要

A drilling apparatus having a central axis 18 and comprising a drill bit 14 arranged to be offset from and hence orbit that axis 18, wherein part of the cutting surface of the drill bit 14 intersects the axis 18 throughout its orbit. The device may further incorporate a housing 12 which acts as a further cutting means and it may include more than one drag bit. The driving means may comprise a planetary gear system.