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Updated: May 5, 2025
When working with rock drills, a shaft can be sunk 10 to 20 feet a month, against 7 to 8 feet by hand, and a level may on the average be driven 45 to 50 feet a month by rock drills against 10 or 12 feet by hand. When, however, a large surface for operating on is exposed, hand-drilling may be profitably employed.
I inspected the works and the rock drills. These work through the agency of compressed air, and at a cost of 15 rupees a day for coal for each drill, the same tool which is used in drilling by hand. It is doubtful whether hand-drilling is not cheaper, but the latter is far slower, and hence does not pay as well, rapid progress being absolutely essential.
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