Abstract: A tool body defines an axis of rotation for the tool and has a periphery surrounding said axis. A plurality of cutter bits are carried by said body and protrude substantially radially from said periphery and have free ends. Said cutter bits are arranged in a plurality of groups which are spaced in the direction of said axis. The free ends of the cutter bits of each of said groups define a circle. The circles defined by the free ends of the cutter bits of said groups increase in diameter in one direction along said axis.

Abstract: Apparatus for drilling holes and installing roof bolts therein for the support of a mine roof includes a prime mover operably connected to a mobile body portion having a pair of spaced apart individually operated drill units. Each drill unit is movably supported on a horizontal frame portion of the mobile body portion by a carriage. The carriage is reciprocally mounted on a plurality of parallel spaced transversely extending beam members that are rigidly secured to the horizontal frame portion. A fluid actuated piston cylinder assembly connected to the carriage is operable to transversely move the carriage with the drill unit along a path transverse to the longitudinal axis of the mobile body portion for drilling holes at preselected spaced intervals in the mine roof. The movement of the carriage is remotely controlled from an operator's station that is protected by an overhead canopy.

Abstract: Concrete structures including horizontal structures such as slabs, sub-beams and main beams and vertical structures such as internal walls, external walls and columns are broken by a static load applied to the concrete structure by a loading member of a static loading means, which causes bending stress to build up in the concrete structure and finally brings about breakage of the structure. The static load may be applied by hydraulic means, preferably mounted on a movable vehicle.