Fig. 3 illustrates a spring-tooth harrow. In this harrow the
independent frames are carried upon wheels, and a seat for the
operator is mounted upon standards supported by the two frames. The
teeth consist of flat steel springs of scroll form, which yield to
rigid obstructions and are mounted on rock shafts in the same manner
as in the walking harrow before described. The levers enable the
operator to raise the teeth more or less, and thus free them from
rubbish and also regulate the depth of action.
[Illustration: FIG. 3.--Spring-tooth Harrow.]
Another variation of the harrow with great pulverizing and loosening
capabilities consists of a main frame, having a pole and whipple-trees
attached: to this frame are pivoted two supplemental frames, each of
which has mounted on it a shaft carrying a series of concavo-convex
disks. The supplemental frames may be swung by the adjusting levers to
any angle with relation to the line of draught, and the disks then act
like that of the disk plough (see PLOUGH), throwing the soil outward
with more or less force, according to the angle at which they are set,
and thus thoroughly breaking up and pulverizing the clods. Above the
disks is a bar to which are pivoted a series of scrapers, one for each
disk, which are held to their work with a yielding action, being
thrown out of operation when desired by the levers shown in connexion
with the operating bar. Pans on the main frame are used to carry
weights to hold the disks down to their work. The cut away disk harrow
differs from the ordinary disk harrow in that its disks are notched
and so have greater penetrating power. The curved knife-tooth harrow
consists of a frame to which a row of curved blades is attached. Other
forms of the implement are illustrated and discussed in _Farm
Machinery and Farm Motors_ by J. B. Davidson and L. W. Chase (New
York, 1908).