Stothert & Pitt with this
modification, and as far as can be judged from the trial with proof
load, the arrangements can hardly be surpassed for quick and accurate
block-setting. In cranes with "derricking" jibs it is necessary to
connect the derrick and hoisting gears in such a manner that a
variation of the radius may not affect the level of the load; this
plan answers sufficiently well for ordinary purposes, but for
block-setting it is requisite to have extreme accuracy in all the
movements and great quickness in changing from one to another; the
arrangements adopted in foundry cranes, in which all the motions are
entirely independent of one another, seems therefore more suited for
this kind of work. Other not inconsiderable advantages are also
secured by the adoption of the foundry crane type, the amount of clear
headway under the jib being much increased, and the difficulty avoided
of making a jib sixty feet long sufficiently stiff without undue
weight.
The principal dimensions of the crane are, total height of lift 46
feet, radius variable from 25 feet minimum to 45 feet maximum, height
from rail to underside of jib 22 feet 23/4 inches, radius of tail to
center of boiler 22 feet, working load 15 tons, proof load 19 tons.
The general arrangement consists of a truck on which is fixed a post,
round which the crane revolves; the jib is supported midway by an
inclined strut, above which is placed the king-post; the strut is
curved round at the bottom and forms one piece with the side frames,
which are carried right back as a tail to support the boiler and
balance weight.
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