. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. k, granite, and other uniform rocks the + bit does goodwork, and drills a round hole because the rock is uniformly hard, andthe drilling is consequently slow. The Z bit, shown in the illustration, is designed and used to amoderate extent in soft rocks, or in work where seams and soft places SHARPENING TOOLS FOR DRILL BITS. 191 are found in the line of the hole. This bit is sometimes modified byhaving the middle edge straight across, thus making an ^ instead of aZ, but there is
. Machinery for metalliferous mines : a practical treatise for mining engineers, metallurgists and managers of mines. k, granite, and other uniform rocks the + bit does goodwork, and drills a round hole because the rock is uniformly hard, andthe drilling is consequently slow. The Z bit, shown in the illustration, is designed and used to amoderate extent in soft rocks, or in work where seams and soft places SHARPENING TOOLS FOR DRILL BITS. 191 are found in the line of the hole. This bit is sometimes modified byhaving the middle edge straight across, thus making an ^ instead of aZ, but there is little preference between the two, and either one isbad enough for the blacksmith to dress. To summarise, in gneiss and homogeneous rocks free from faults,the ordinary chisel-shaped bit is to be preferred, as it, perhaps, in suchrocks, cuts faster than any other shape of bit, and smiths can morereadily sharpen it. In schistose rocks wherein layers of uneven hardness,with numerous fissures are encountered, the chisel bit does not answerso satisfactorily, as the drill seeks the softer material, gets out J of line,.
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyo, bookyear1902
