270 



LOGGING 



One man can operate a drill for holes 3 feet or under in depth, two 

 men for those of medium depth and three or four men for the 

 deepest holes. 



Trautwine gives the following as an average ten hours' work 

 for a churn drill: 



Character of rock. 



Hard gneiss, granite or silicious limestone 



Tough compact hornblende 



Solid quartz 



Ordinary limestone 



Sandstone 



Feet. 



7 to 8 

 5 to 7 

 3 to 5 



8 to 9 



9 to 10 



Jumper Drill. — These are shorter than churn drills and are 

 operated by two or more men, one of whom sitting down holds the 

 drill and revolves it about | of a revolution after each stroke, 

 while the other men strike the drill head with 8- or 12-pound 

 sledge hammers. 



The drill rods are of |-inch octagon steel and the bits are i^ 

 or i| inches wide. The maximum depth for efficient work with 

 a three-man jumper drill ranges between 6 and 8 feet. 



Since it can be held on the exact spot, this drill can be used 

 for 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, one 

 holder and two strikers, using a jumper is approximately as fol- 

 lows for 6-foot holes :^ 



Character of rock. 



Granite 



Trap (basalt). 

 Limestone. . . . 



Hand Drill. — The hand drilling method is similar to jump 

 drilling, except that the operator sitting down holds the drill with 



1 From "Handbook of Cost Data," by H. B. Gillette. Myron C. Clark Pub- 

 lishing Co., Chicago, III., 19 lo. P. 185. 



