Fig. 118
An improved winch with an advantage over those ordinarily used has the drum grooved in three diameters, so that, with a minimum of trouble, a choice of mechanical advantages is gained. There is no need with these winches to pass the rope several times round the drum, for as the rope works in a groove, greater friction is set up; and the clutches provided to keep the rope in contact with the barrel for three quarters of its circumference, still further prevent any likelihood of slipping.
Fig. 119
Jibs.—For the fixing of the gear a jib ([fig. 119]) is sufficient to carry a fixed pulley. A jib is a single pole attached horizontally to the standards or ledgers above the platform upon which it is intended to deposit the material. It should project slightly more than half the width of the load to be hoisted, usually from 18 inches to 2 feet.
Fig. 120
It is useful at times to have a pulley block fixed over the work in hand, especially for fixing purposes. In these cases, the loads being usually heavy, the jib requires extra support, which is obtained by fixing it as a continuous beam supported at both ends ([fig. 120]). This is arranged by carrying up on the interior of the building a series of standards and ledgers; these rise from each floor as the work proceeds. The jib can be carried right across the work in hand and the gear fixed as required.
