An impact type of anvil core bit includes a body having a central opening through its bottom drilling face, a plurality of spaced cutters, such as sintered tungsten carbide buttons, being secured to the body and extending downwardly from the face to drill against the bottom of the bore hole outwardly of the central opening, the cutters including inner cutters for forming the core in the bottom of the hole, a cutter ring being secured to the body and circumscribing the opening above the bottom of the hole to shape the core for movement into the central opening.
An annular drilling hammer having an annular bore crown guided between an outer tube and an inner tube. An annular hammer piston periodically strikes the bore crown and has a piston member that is guided in a cylindrical chamber having control apertures which are connected fluidically to a reversing valve. The working medium is delivered to the reversing valve between an inner tube system and an outer tube system. After driving the hammer piston the medium is discharged from the drill between the outer tube and the bore crown. The bore crown is provided with flow channels leading from the rear shoulder through and to the front and/or central aperture of the bore crown. The flow of driving medium through these channels aids the entrainment of bored material, which then is carried out through the inner tube with the aid of a Venturi opening.
A method and apparatus for boring a hole in the earth including a drill bit assembly including a fluid-powered impact engine contained within a drillpipe sub between an ordinary drillpipe and a modified conventional rotary drill bit. The impact engine is powered by pressurized drilling fluid delivered via the drillpipe which acts on a piston to charge an energy accumulator, preferably in the form of a spring. Periodically, the pressurized drilling fluid in the impact engine is vented, allowing the energy accumulator to rapidly transfer its stored energy to an impact bit which is slidingly housed in a rotary bit to strike and fracture the formation.
