EXCAVATING MACHINERY USED IN LAND DRAINAGE. 19 



In the smaller drag-line machines the boom is generally constructed 

 of two channels with cross bracing, while for the larger machines two 

 cross-braced lattice girders are used. The lower ends of the two 

 main members of the boom are spread apart to give stability, while 

 at the upper end the two members are joined, at which point one or 

 more sheaves are placed. The top of the boom is guyed to the top 

 of the A frame which is located near the front of the main engine. 

 The lower ends of the A frame are bolted to the platform while the 

 upper end is guyed to the rear corners of the platform. 



The bucket most frequently used on drag-line excavators is of the 

 scraper type, although the clam-shell and orange-peel buckets are 

 sometimes used for special work. The scraper bucket is connected 

 to the main engine by two steel cables called respectively the hoist- 

 ing and drag-line cables. The bucket is filled by being pulled toward 

 the machine, and when full is raised by the hoisting cable which 

 passes from the bucket over the sheaves in the end of the boom and 

 down to the hoisting drum. There are many patented devices for 

 quickly dumping the bucket, a feature that is important in digging 

 sticky material. The capacity of the scraper buckets range from 

 about five-eighths cubic yard to 3 cubic yards. 



The crew necessary to operate this type of machine consists of two 

 men, an operator and a fireman on the steam machine, or an operator 

 and an oiler on the gasoline or electrically-driven machines. In 

 addition to these, two or more trackmen are required, except in the 

 case of the so-called walking type. 



For movement over the ground the drag-line excavator may be 

 mounted on either wheels, rollers, caterpillar tractors, trucks, or 

 walking shoes. 



Where the ground is uneven or cut up with old channels and sur- 

 face ditches, it is necessary in the case of all traction or roller exca- 

 vators which are not of the rotary type to block or bridge across the 

 depressions and to lay heavy timbers on which to move the machine. 

 Where the machine weighs 25 tons or more the expense of providing 

 a solid foundation becomes quite great. In the rotary type of exca- 

 vator the machine can be revolved and can build its own foundation 

 of earth. 



Drag-line excavators vary greatly in weight, not only with the 

 capacity of the machine but with the manufacturer. Some of the 

 five-eighths-yard stationary types weigh no more than 12 tons. 

 There are a few standard makes of drag-line excavators which, 

 although they may differ in details of construction, are operated in 

 the same manner. They vary in weight from 25 tons to about 110 

 tons. It is especially noteworthy that in all makes the heavier 

 machines are mounted on wooden rollers or on trucks to run on a 

 track. Wheels and caterpillar traction are used only on the lighter 



