Page 34 - Moving the Earth_ The Workbook of Excavation

LAND CLEARING AND CONTROLS

1.34 THE WORK

FIGURE 1.26A Use of sling block.

to a heavier line which passes around another pulley to an anchor. The second pulley is pulled
with almost four times the power of the winch.
The sling block makes possible the use of a double choker on the tree being pulled. The choker
cable is approximately centered in the sling pulley, and both ends are hooked around the tree. Such
a double choker can be of lighter and more flexible cable than a single choker.
Rigging. Multiple blocks require care in rigging and pulling. Two anchors are better than one, as
they spread the cables over a wider space where they are less apt to interfere with each other. Each
block is best fastened to a separate choker, but one may be fastened to each end of a chain passed
behind the stump if it is strong enough to take a double pull; or one to both ends of a chain given
one turn around the stump. It is good practice to notch the stump for each chain used, so that the
chains and blocks will not slide into each other as it yields.
Rigging is done with the lines slack. When they are pulled tight, an inspection should be made
to make sure that no pulley latches have fallen open, as a pull on an open block will bend it and
cut the cable; that no pulleys are jammed with debris, or liable to pull into each other; and that no
chain hooks have become disengaged. As the line is wound in, all blocks should be watched to
make certain that they do not collide. Lines should not be allowed to drag on each other.
If the winch does not carry sufficient line for the distance or the number of lines involved, extra
line can be added by the use of a take-up block, as in Fig. 1.26B. A standard practice is to use the
winch line from the tractor to near the first snatch block, and the extra line for reeving. The take-up
cannot be pulled through a snatch block, and is liable to cause trouble if included in the multiple lines.
The extra line is often carried on a spool supported on a pipe axle and brackets. This should
have a drag brake of some kind, to prevent spinning when paying out. The brake might consist
only of a log leaned against the face or side, or a worker’s gloved hand.

Anchors. It is often a question of whether the stump or the anchor will yield. Anchor lines should
be as low as possible and stump lines high. It may be best to pull the largest stumps first, using sev-
eral smaller ones for anchorage if necessary. In a clean-clearing job, there is always one last stump
for which there is no anchor, and if it is small, it may be pulled out directly; or in any case it will
respond to less elaborate artificial anchors than a large one. On the other hand, a large stump will
be a dependable anchor, and will prevent the need of frequent rerigging when anchors pull out.