The encyclopdia britannica; a dictionary of arts, sciences, literature and general information . Fig. 9. Fig. Fig. 6.—New IngersoU Drill. others the drill-bit is caused to reciprocate by means of combinationsof crank and spring. None of these machines is entirely satisfactory,and but few are in use. Among percussion rock-drills operated by electricity are theBladray, Box, Durkee, Marvin and Siemens-Halske. The Marvindrill works with a solenoid; most of the others have crank and springmovements for producing the reciprocations of the piston. Poweris furnished by a small electric motor, eit
The encyclopdia britannica; a dictionary of arts, sciences, literature and general information . Fig. 9. Fig. Fig. 6.—New IngersoU Drill. others the drill-bit is caused to reciprocate by means of combinationsof crank and spring. None of these machines is entirely satisfactory,and but few are in use. Among percussion rock-drills operated by electricity are theBladray, Box, Durkee, Marvin and Siemens-Halske. The Marvindrill works with a solenoid; most of the others have crank and springmovements for producing the reciprocations of the piston. Poweris furnished by a small electric motor, either mounted on the machineitself, as with the Box drill, or more often standing on the groundand transmitting its power through a flexible shaft. Although ratherfrequently used, electric percussion drills cannot yet be consideredentirely successful, at least for mine service, in competition withcompressed air machines. Another type of electric drill, however. some degree of symmetry, in roughly concentric rings, as shownby figs. 9 and 10. The centre holes are blasted first, and arefollowed^ by the others in
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectencyclo, bookyear1910
