=23. Guides= are used in all vertical shafts of any considerable depth
and in many highly inclined shafts to keep the cage from swinging
about and striking the sides of the shaft. They are made of wooden
rails, iron rails, or wire ropes. In American mines, timber guides
predominate, although some iron ones are used, and for small shafts
at ore mines wire-rope guides are common. In English mines, wire
ropes, called _conductors_, are very largely used. This difference
in practice is probably due to the fact that in English mines the
shafts are usually round and the cages are rectangular. In such a
shaft, the wire-rope conductors hang from the head-frame without any
cross-bracing, but they require a strong support, as both the weight
of the ropes and the strain to give the necessary tension come on the
head-frame. When both the shaft and the cage are rectangular, as in
most American mines, timber guides are easily put in and they offer a
good surface for the safety catches to grip.
[Illustration: FIG. 23]
Wooden guides are always rectangular in cross-section and in the United
States are usually made of yellow pine or other long-grained wood that
does not splinter easily; in some localities, oak or some of the other
harder woods are used. There is no fixed size for cage guides, but 4" ×
4", 6" × 8", 8" × 10", and 4¼" × 11" timbers are frequently used.
The guides are firmly fastened to the shaft buntons with lagscrews or
with bolts countersunk into the guide so as to be clear of the shoes,
and, to secure safety with speed in hoisting, the ends of the guides
must be put together with joints that are not liable to displacement
and that offer no projections to the shoes in passing. The buntons
to which the guides are secured must be so firmly fastened that they
cannot get out of place, and the guides must be set as nearly as
possible in a straight line, because if they are crooked the cage
is thrown back and forth as it travels along them and this not only
increases the strain on the hoisting rope and engine, but sooner or
later loosens and misplaces the guide. Fig. 23 shows a plan of a cage
with the bunton _A_, guides _B_, and cage shoes _C_ in their normal
positions.