Handbook of construction plant, its cost and efficiency (1914)
Dana, Richard Turner, 1876-1928 · Chicago, The M. C. Clark Publishing Co. · leaf 260
^ *~.--ki£Nv … Fig. 89. Drilling Down Holes with the Little imp 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 iys…
Contractors' operations · Building
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