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A rotary drill with two hardened knurled cones which cut the rock as they roll. Also known as roller bit.

Related Terms


The speed at which a drill can cut through rock or other material. penetration test


A rock-drilling method performed by two men, one striking the rock with a long-handled sledge hammer while a second holds the drill and twists it between strokes. Also known as double jacking.


An instrument used to measure small distances in the field of an eyepiece by using two parallel wires, one of which is fixed while the other is moved at right angles to its length by means of an accurately cut screw. Also known as bifilar micrometer.


A surface blasting method used when no rock drill is necessary or one is not available; consists of placing a charge of gelignite, primed with safety fuse and detonator, in close contact with the rock or boulder and covering it completely with stiff damp clay.


An electrode array used in a lateral search conducted during a resistivity or induced polarization survey, or in drill hole logging, in which one current electrode is placed at infinity while another current electrode and two potential electrodes in proximity are moved across the structure to be investigated.


1.The restoration of the diameter of a borehole by reaming. 2. The breaking down of the walls between two contiguous drill holes. 3. The machine-shaping of metal or plastic by pushing or pulling a broach across a surface or through an existing hole in a workpiece.


  1. A small artificial channel cut through earth or rock to carry water for irrigation or drainage. 2. A long narrow cut made in the earth to bury pipeline, cable, or similar installations.


Total weight or pressure, expressed in pounds or tons, applied to the drilling stem to make the drill bit cut and penetrate the geologic, rock, or ore formation.


A machine for breaking rock between two steel jaws, one fixed and the other swinging. Also known as jawbreaker.


A general type of bit made in many shapes which does not produce a core and with which all the rock cut in a borehole is ejected as sludge; used mostly for blasthole drilling and in the unmineralized zones in a borehole where a core sample is not wanted. Also known as borehole bit; plug bit.

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