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 P. Tools and machinery of the granite industry. In: Chronicle of the Early American Industries Association, 2006: 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 four-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 nine-pound sledgehammer.
Jacking was a severe test of strength and endurance. In a drilling contest, a quarryman single-handedly drilled a hole in granite 673mm (26.5 inches) deep in 15 minutes. A double jacking team drilled a hole in granite 1515mm (59.6 inches) deep in 15 minutes. However, for production drilling, single-jacking might make 203mm (eight inches) of hole in an hour in rock of average hardness; double-jacking might make two feet.
In very hard rock, 12 hours of double-jacking might make less than 25mm (roughly one 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 51mm to 152mm (two to six 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 1400 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, John George Leyner, by adapting techniques for boring gun barrels, developed a hammer drill with a hollow drill bit. His drill blew the cuttings from the hole with a jet of air through the centre 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?