. The elements of railroad engineering . Fig. 417. 932 RAILROAD CONSTRUCTION. working of the drills. The arm E at right angles to thecolumn slides up or down the column by means of the collar F, and may be clampedin any position by the clamp drill is carried on this armand revolves about it as an axis,thus giving a wide range ofaction. Usually two drills aremounted on each column. Insinking shafts and driving tun-nels, as well as in mine work,compressed air is used instead ofsteam, which loses much of itspressure through use of compressed air greatlypromotes ventilation.
. The elements of railroad engineering . Fig. 417. 932 RAILROAD CONSTRUCTION. working of the drills. The arm E at right angles to thecolumn slides up or down the column by means of the collar F, and may be clampedin any position by the clamp drill is carried on this armand revolves about it as an axis,thus giving a wide range ofaction. Usually two drills aremounted on each column. Insinking shafts and driving tun-nels, as well as in mine work,compressed air is used instead ofsteam, which loses much of itspressure through use of compressed air greatlypromotes ventilation. Percus-sion drills are under a pressureof from 60 to 70 lb. per squareinch. In one hour one will drilla hole froni 2 to 2^ inches indiameter and from 4 to 10 feetin depth, depending upon thecharacter of the rock, the positionof the strata, and the size of themachine. The cost of drillingwill vary from 8 to 20 cents perFig. 418 lineal 15()1. Drill-bits are of different shapes, beingvaried to suit the work to be done. For uniform hard rock,the bit is cross-shaped, with the arms of equal length and atright angles to each other. For seamy rock, the arms ofthe bits are of equal length, but cross each other X soft rock, frequently a bit with a Z-shaped cutting edgeis used. Fig. 419 shows the usual form of drill-bit, and Fig. 420 thetool for sharpening same. On surface work, a drill isusually worked by one man; in tunnel work, two men are RAILROAD CONSTRUCTION. 933 commonly employed. The man in charge of the drill iscalled the drill runner and his assistant the helper or or four men are requiredin moving and placing the largerdrills. I
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
