Bore bit for very hard material

摘要

An apparatus including a bore bit comprising a bottom part having an active bottom face and a top face substantially parallel to the active face; a top part fixed to suspension cables and having a bottom face facing the top face of the bottom part; a member for limiting the maximum spacing between the two parts; a cylindrical axial bore passing through both parts; a cylindrical guide penetrating into said bore; and at least one ramp-forming recess and at least one ramp-forming extension for co-operating with said ramp-forming recess in such a manner that movement of the top part towards the bottom part is converted into rotary movement of said top part about the vertical axis, with the end of said rotary movement of the top part imparting rotary movement to the bottom part.