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Carved in Stone
Posted By Brooke Wisdom On October 1, 2010 @ 6:00 am In Articles,Carved In Stone,Departments | No Comments
J is for Jack
The early days of drilling created a test of strength and endurance for miners.
By Bill Langer
Jack (n.) — used as a form of address for an unknown person — ‘It is common among schoolboys … to address a stranger as Jack’ (Barrére and Leland, 1889, Dictionary of slang, Vol. 1, p. 490); (v.) a method of drilling a hole in rock — ‘It is believed that the terms single and double jacking came from “Cousin Jack,” a nickname for a Cornish miner.’ (Wood, 2006, Tools and machinery of the granite industry, p. 45).
In the late 19th century, most rock drilling was done by ‘jacking.’ Single-jacking was when one man would hold a drill rod, strike the drill with a 4-pound hammer, and on the backswing, give the drill a twist so that on the next blow the drill would impact fresh rock. Double-jacking was used for deeper holes where one man would hold and twist the drill rod while his partner struck it with a 9-pound sledgehammer.
Jacking was a severe test of strength and endurance. In a drilling contest, a quarryman single-handedly drilled a hole in granite 26 1/2-inches deep in 15 minutes. A double-jacking team drilled a hole in granite 59 5/8-inches deep in 15 minutes. However, for production drilling, single-jacking in rock of average hardness might yield 8 inches of hole in an hour; double-jacking might make 2 feet. In very hard rock, 12 hours of double-jacking might make less than 1 inch of progress. Old miners would talk about working all day in rock so hard that they had to leave a man behind with his finger on the spot where they had been drilling so the next shift could pick up where they left off.
Jacking was not efficient enough to meet the increasing demand for mined and quarried material. Improvements came circa 1870 in the form of steam and pneumatic piston or “slugger” drills. The drills contained solid drill rods firmly clamped to a piston and were mounted on tripods to support their weight and resist recoil. Some piston drills ran from 200 to 600 strokes per minute and penetrated at a rate of 2 to 6 inches per minute.
The hammer drill, invented in the early 1890s, operated by having a piston hammer strike the end of a drill rod that slid freely in a chuck. The drill was not attached to the piston, so the piston could move faster — around 1,400 strokes per minute. The drills were known as ‘buzzies’ because of their high speed, but the hammer drill could not be used in downward holes because there was no way to get rid of the powdery cuttings that cushioned the blows. Buzzies could only be used in applications where the dust would fall out of the hole by gravity. Consequently, they were also known as ‘widow makers’ because, when used to drill in granite and other silica-rich rocks, the dust falling out of the drill holes and inhaled by miners could cause deadly silicosis.
In the late 1890s, J. George Leyner adapted techniques for boring gun barrels and developed a hammer drill with a hollow drill bit. His drill blew the cuttings from the hole with a jet of air through the center of the drill rod and wetted the dust with water injected through the drill steel. His invention greatly reduced the amount of airborne dust from drilling and probably spared thousands of granite quarrymen and miners from early deaths from silicosis.
Pretty cool, ’eh Jack?
Bill Langer is a geologist with the Mineral Resources Team of the U.S. Geological Survey and can be reached at 303-236-1249 or via e-mail at firstname.lastname@example.org.
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