288 



ENGINEERING ON THE FARM 



the labor necessary for the construction of large systems. 

 In caving materials a sheathing attachment is pulled with 

 the machine to prevent caving before the tile is in place. A 

 crane attached to the rear of the machine may be used to 

 lower the tile. The tile is laid by workmen. The machines 

 are expensive and require experience and mechanical skill 

 in operation and are suitable for farm use only when handled 

 by contractors who make a business of ditch construction. 

 Grading. The grading of tile trenches is very important, 

 and there are several methods equally good that are in com- 

 mon use. The method of using cross lines is as simple and 

 satisfactory as any. The line of the ditch is marked out by 

 stakes left by the surveyor. The stakes may be 50 or 100 

 feet apart. There are two stakes in a place, one with the top 

 driven level with the surface of the ground, known as the 



After University of Minnesota 



Fig. 236. Method of grading the bottom of a trench for tile 



hub, and the other standing a foot or more above the ground, 

 called the guard. The hub stake is the one from which all 

 measurements are made. The guard stake, driven a couple 



