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A modern core drill is a drill specifically designed to remove a cylinder of material, much like a hole saw. The material left inside the drill bit is referred to as the core.
Core drills used in metal are called annular cutters. Core drills used for concrete and hard rock generally use industrial diamond grit as the abrasive material and may be electrical, pneumatic or hydraulic powered. Core drills are commonly water cooled, and the water also carries away the fine waste as a slurry. For drilling masonry, carbide core drills can be used, but diamond is more successful when cutting through rebar.
The earliest core drills were those used by the ancient Egyptians, invented in 3000 BC. Core drills are used for many applications, either where the core needs to be preserved , or where drilling can be done more rapidly since much less material needs to be removed than with a standard bit. This is the reason that diamond-tipped core drills are commonly used in construction to create holes for pipes, manholes, and other large-diameter penetrations in concrete or stone.
Core drills are used frequently in mineral exploration where the coring may be several hundred to several thousand feet in length. The core samples are recovered and examined by geologists for mineral percentages and stratigraphic contact points. This gives exploration companies the information necessary to begin or abandon mining operations in a particular area.