Chicago : Engineering and Contracting Pub. Co. · leaf 313
t handicappedas under the former system. The tripod machine has drilled as high as96 ft. of 12-ft. holes in a 10-hr. day, whilewith the hammer drills 93 ft. is an excellentdays work and 65 ft. more nearly the average. A good contract quarryman, drilling byhand, would average 8 ft. of deep hole… … Fig. 1. Hammer Drills for Drilling Holes 8 Ft. Deep at Jacksboro, Texas. air or steam drills for all of the purposes towhich they might be applied profitably. Thedevelopment of the hand feed air hammerdrill now enables hand drilling to be dispensedwith entirely, at a great saving of time, laborand…
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