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An Improved Drill for Drilling Coal and other Substances.
An Improved Drill for Drilling Coal and other Substances.
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机译:一种用于钻探煤炭和其他物质的改进型钻头。
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摘要
11,565. Timmins, W., and Engelrest, J. May 21. Rock drills, rotary. Twist drills are formed to bore a smaller hole in advance of the cutting- edges a, by means of the cutting-edges b, which may or may not be re-entrant.
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