Logging; the principles and general methods of operation in the United States . t of rock moved and the difficulties of trans-porting drilling machinery and equipment to the site of the work. There are three forms of drills used for hand work; namely,the churn drill, the jumper drill and the hand drill. Churn Drill. — This is the most economical form of drill forholes up to 30 feet in depth and from i| to 2^ inches in diameter. The drill consists of a i|- or i^-inch round iron bar of therequired length, on one end of which is welded a steel chisel bitfrom 30 to 100 per cent wider than the diam
Logging; the principles and general methods of operation in the United States . t of rock moved and the difficulties of trans-porting drilling machinery and equipment to the site of the work. There are three forms of drills used for hand work; namely,the churn drill, the jumper drill and the hand drill. Churn Drill. — This is the most economical form of drill forholes up to 30 feet in depth and from i| to 2^ inches in diameter. The drill consists of a i|- or i^-inch round iron bar of therequired length, on one end of which is welded a steel chisel bitfrom 30 to 100 per cent wider than the diameter of the rods of different lengths are required for drilling a deephole. The drill is operated by raising it from 18 to 24 inches andallowing it to drop, the weight of the drill furnishing the power. 270 LOGGING One man can operate a drill for holes 3 feet or under in depth, twomen for those of medium depth and three or four men for thedeepest holes. Trautwine gives the following as an average ten hours workfor a churn drill: Character of rock. Depth Hard gneiss, granite or silicious limestone Tough compact hornblende Solid quartz Ordinary limestone Sandstone to 10 Jumper Drill. — These are shorter than churn drills and areoperated by two or more men, one of whom sitting down holds thedrill and revolves it about | of a revolution after each stroke,while the other men strike the drill head with 8- or 12-poundsledge hammers. The drill rods are of |-inch octagon steel and the bits are i^or i\ inches wide. The maximum depth for efhcient work witha three-man jumper drill ranges between 6 and 8 feet. Since it can be held on the exact spot, this drill can be usedfor smaller holes than a churn drill. It is also best for con-glomerate rock, because it is not so easily deflected by pebbles. The amount of work performed in ten hours by three men, oneholder and two strikers, using a jumper is approximately as fol-lows for 6-foot holes :^ Character of rock. Feet.
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Keywords: ., bookcentury1900, bookdecade1910, bookpublisheretcet, bookyear1913
