Handbook of construction plant, its cost and efficiency (1918)
Dana, Richard Turner, 1876-1928 · New York, McGraw-Hill book company, inc., [etc., etc.] · leaf 260
89. Drilling Down Holes with the Little !mp Drill. Fig. 88. Drilling Up Holes with the Little Imp Air Feed Drill. per shift. One blacksmith with a helper will keep 5 to 7drills supplied with sharp bits. In medium rock a bit must besharpened for each 2 ft. of hole, in hard rock, for each lYz ft.,and… … Fig. 89 A. Mr. T. H. Proskesays: The power drill-sharpener has re-moved many of theshortcomings attend-ant upon the handsharpening process,with the result thatwhere these machinesare used it is possibleto accomplish from 25to 100 per cent moredrilling than underthe old methods. Itake this to mean…
Contractors' operations · Building
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