49 BULLETIN 300, U. S. DEPARTMENT OF AGRICULTURE. 
ACCESSORY EQUIPMENT. 
For housing men employed in the operation of drag-line excavators 
many contractors use camp wagons, consisting of portable houses 
mounted on wagons. The most common size is 8 feet wide by 18 feet 
long. The structure costs about $200 and a wagon with 4-inch 
tires about $100. 
SELECTION OF SCRAPER EXCAVATOR. 
In selecting a scraper excavator, the purchaser, in addition to 
choosing the most desirable kind of power and the means of moving 
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REACH OF BOOM /N FEET FROM CENTER Of BOOM LUG AT VARIOUS ANGLES. 
To This Distance add “A” when Distance trom Center of Machine 1s reguired 
. a . . 
lic. 2.—Diagram of scraper excavator showing relation between the length of boom and 
the effective reach of machine. 
over the ground best suited to his particular case, must determine the 
length of boom best suited to his needs. 
Figure 2 is a diagram showing the relation between the length and 
angle of elevation of the boom and the effective reach of the machine. 
In this diagram all distances are referred to the heel of the boom. 
If it is desired to refer horizontal distances to the center of the 
machine, the correction A must, of course, be added; this distance 
varies somewhat with the different makes of machine. The distance B 
of the heel of the boom above the ground likewise varies slightly in 
different machines. 
To determine the maximum clearance of the bucket above the 
ground for different lengths and positions of boom the distance B 
must be added to the vertical heights given on the right-hand margin 
of the diagram, and from this sum must be subtracted the distance C 
