A familiar sound and sight was once the rhythmic tapping of the hammer of the stonebreaker as he sat by his heap at the side of the road. Even this simple operation is now generally performed mechanically. Road metal, when it is used at all, is prepared in crushing machines and carted to where it is required. These machines, which may be likened to gigantic nutcrackers, bear no resemblance to a hammer; but American engineering has produced a machine which almost exactly reproduces, on a greatly enlarged scale, the roadmender’s hammer.
A machine of this type is shown in the photograph below. It is not used, however, for preparing road metal, but for breaking up rocks and boulders into pieces which can be readily removed, such clearance of the ground being more frequently necessary in the less thickly populated regions of the United States than in Great Britain. The machine, too, is not built specially for this purpose. It forms another application of the excavating machine which can already be used in a variety of ways - for instance, with a bucket for gnawing away a bank. The excavating machine is adapted for its various duties by alterations to the parts carried on the jib or boom, the mighty hammer here shown being one such form of alteration. The body of the machine is mounted on the now familiar crawlers for movement from place to place, and is also capable of being slewed round in a circle on the crawler chassis. The jib can be raised or lowered in the same way as that of a crane. The hammer, however, is not rigidly attached to the jib, but its “handle” is hinged as shown. Not only, then, can it be allowed to fall by slackening the jib ropes, but, by tightening the hammer rope at the appropriate moment, additional force can be given to the blow.
The hammer weighs about 1⅜ tons and can be dropped from any height between 5 feet and 10 feet at the rate of twenty blows a minute. The hammer is shown at the bottom of the photograph smashing up pieces of rock lying on the ground. It can be used in this position also for such purposes as breaking up metals in the foundry or scrap heap or for consolidating loose earth. But this is not all; by a rearrangement of the hammer and ropes, the machine can be made to give a blow against a vertical surface. It can thus be used for demolishing walls or small structures.
The face of the hammer is made so that it can be altered to suit the particular job the machine is to be used for. Thus a convex face may be desirable for breaking material or a flat face for tamping, while a pointed face may be fitted so that the effect of a gigantic pick-axe is secured. The driving machinery is that generally fitted to excavating machines - an internal combustion engine with suitable winches and so forth.