24 
BULLETIN 463, U. S. DEPARTMENT OF AGRICULTURE, 
Fig. 13. — Breaking up clods with a disk harrow. 
very tenacious it should be harrowed with a disk harrow (fig. 13) 
ahead of the grading machine, and after the material has been 
moved over toward the center of the road the lumps of sod should be 
thrown out. A method sometimes followed is to skim off the sod, 
by means of hand shovels, ahead of the grading machine, but this 
method is expensive and seldom justified. 
Whether or not it is necessary to contend with any considerable 
quantit}^ of sod, the use of a disk harrow usually will prove helpful 
in securing a smooth uniform road surface with the grading machine. 
In general it is sufficient to give the loosened material a thorough 
harrowing after the road has been brought approximately to its 
required shape, but 
before the final shap- 
ing is done. 
Where continuous 
long stretches of road 
are to be graded with 
grading machines, it 
frequently is econom- 
ical to substitute a 
traction engine for 
the teams and to em- 
ploy two machines. 
Where this is done 
the first machine is 
connected immedi- 
ately behind the trac- 
tor, either directly 
behind or to one side, as the conditions require, and the second 
machine is connected behind and to one side of the first. Otherwise 
the method of operation is not essentially different from that already 
described. 
The rate at which a road can be graded up with a grading machine 
varies to a great extent, and depends largely on the character of 
the soil. Where the original cross section of the ground is approxi- 
mately level, such as that shown in the model (PL II). the cross 
section of the finished road similar to that shown in figure 12, and 
the soil conditions not unfavorable, a grading machine drawn by six 
well-trained horses should cut out the side ditches and shape the road 
in from 20 to 35 round trips. Allowing for a reasonable amount 
of lost time, the rate at which the team travels should average from 
11 to 2 miles per hour, and under the circumstances assumed above, 
the length of road graded per day should average not less than 
one-fourth mile. Such favorable conditions seldom are found for 
any considerable stretch of road, except in the prairie sections of the 
