Core drill

Truck-mounted core drill

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.[1] For drilling masonry, carbide core drills can be used, but diamond is more successful when cutting through rebar.[2]

The earliest core drills were those used by the ancient Egyptians, invented in 3000 BC.[3] Core drills are used for many applications, either where the core needs to be preserved (the drilling apparatus used in obtaining a core sample is often referred to as a corer), 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 drill string 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.

An oriented core goniometer, commonly used when analyzing cores for contacts and other structural features

Before the start of World War Two, John Branner Newsom, a California mining engineer, invented and patented a core drill that could take out large diameter cores (>5 ft.) up to 10 feet in length for mining shafts. [4] This type of shaft-sinking drill is no longer in use as it was cumbersome, prone to jamming with cuttings, thus slow compared to conventional shaft sinking techniques, and only worked effectively in soft rock formations. Modern shaft-sinking technology accomplishes the same faster and at a much cheaper cost.

Core drills come with several power choices including electric, pneumatic, and hydraulic (all of which require power sources, such as a generator).

  1. ^ "Diamond Core Bits vs Carbide Core Bits". 10 December 2012. Retrieved 4 August 2014.
  2. ^ "Concrete Drilling Tutorial". Retrieved 4 August 2014.
  3. ^ Jacques W. Delleur (12 December 2010). The Handbook of Groundwater Engineering, Second Edition. Taylor & Francis. p. 7 in chapter 2. ISBN 978-0-8493-4316-2.
  4. ^ Boone, Andrew R. (December 1943). "He Bores Bigger Holes". Popular Science: 104–107.