Wedges.—A wedge is a movable, double-inclined plane, used for separating bodies, and by this means, tightening any connections between the bodies they tend to separate. For scaffolding purposes they should be of oak, or other wood which gives considerable resistance to pressure across the grain. For tightening cordage wedges should be about 12 inches in length and, as far as possible, split to shape. In cross section they should be semicircular. Their taper should be gradual and not too sudden, as otherwise they might work out. When used in pairs as for shoring purposes, they are rectangular in cross section, and are termed folding wedges.
Nails.—Cut nails stamped out of plates are best for scaffolds. These nails have the advantage of being easily drawn out of timber. When driven with their flat sides the way of the grain, they do not tend to split the wood. They are used to fix platform boards, and sometimes guard boards, on edge.
Spikes.—Spikes are nails above 4 inches in length. They form a cheap method of fixing. Captain Fraser, R.E., has computed from experiments that their holding power in fir is from 460 to 700 pounds per inch of length the depth of cover plate being deducted.
Fig. 104
Scaffolder’s hatchet.—The scaffolder’s hatchet ([fig. 104]) is an ordinary shingling hatchet with a hammer head. It is practically the only tool used by the scaffolder. With it he can shape the ends of the putlogs, drive wedges, nails, &c., and, by giving the cord a turn round the middle of the handle, tighten knots by using it as a lever.
CHAPTER VII
THE TRANSPORT OF MATERIAL
The transportation of material is not altogether within the province of a scaffolder, but it is so intimately connected—indeed, it is difficult to say where his connection with the lifting and carrying of material commences and finishes—that the subject is here briefly commented upon.
Crane Engines.—The engines of the crane are so arranged that all motions in connection with the derrick are under the control of the driver. The engines are double cylinder with link-motion reversing gear. The gearing is single and double purchase for lifting; the jib barrel is fitted with steel catch wheel and double-lock safety catch to prevent the jib running down. The slewing gear is worked from the crank shaft, connected to the upright shaft from bottom race or spur wheel, and is wrought by worm and worm wheel with double-cone friction slewing gear. This arrangement permits of slewing the crane in either direction without reversing the engine. It might also be mentioned that the clutch for the jib motion is hooped with malleable iron to prevent the possibility of its bursting.
Crane engines can be worked by electrical, steam, or manual power. The smaller cranes are now so made that either steam or manual power can be used as required. It is of recent date that these engines have been supplied with electrical power, and of course their use is restricted to where this power is obtainable.