RAILROAD CONSTRUCTION 
305 
by a gasoline cngino, which is moved forward over the proposed 
route in advance of actual rock removal. 
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 for 
holes up to 30 feet in depth and from 1| to 2^ inches in diameter. 
The drill is a IJ- or 1^-inch round iron bar of the nHjuircd 
length, on one end of which is welded a steel chisel bit from 
30 to 100 per cent wider than the diameter of the rod. Several 
rods of different lengths are required for drilling a deep hole. 
The drill is operated by raising it from 18 to 24 inches and 
allowing it to drop. 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 siliceous limestone 
Tough compact hornblende 
Solid quartz 
Ordinary limestone 
Sandstone 
Diameter of 
Depth of 
hole 
hole 
Inches 
Feet 
If 
7 to 8 
If 
5 to 7 
If 
3 to 5 
If 
8 to 9 
If 
9 to 10 
Jumper Drill. — These are shorter than churn drills and are 
operated by two or more men; one, 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 Ij 
or 1^ inches wide. The maximum depth for efficient work with 
a three-man jumper drill does not exceed 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 holes 6 feet in depth :^ 
1 From "Handbook of Rock Excavation," by H. B. Gillette, p. 26. 
