Page:Popular Science Monthly Volume 88.djvu/858

 Trench-Digging by Machinery

��MODERN engineering require- ments coupled with a persistent demand for labor-saving devices have brought into being several types

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� ��Above, the endless chain type of machine excavating a twelve- foot trench with cutting buck- ets. To the right, the wheel type of machine with its driv- ing mechanism at the top

��of trench-digging apparatus which are of ingenious con- struction. Of all manual la- bor, digging trenches by hand or exca\'ating on a large scale by hand is the most laborious and expensive method. One of the largest single items in a contractor's specification, until the modern digging ma- chines came along, concerned

��the amount of excavating to be done. With the several new types of mechani- cal excavators this item can be reduced materially.

In the machines recently marketed two general principles seem to be used. In one, cutting buckets are attached to an endless chain, while in the other they are mounted on the periphery of a wheel. In both methods the buckets are forced to bite into the ground at the end of a trench, carrying the dirt up with them as they rise.

The endless chain type of machine grips the dirt and hoists it to the surface in the same way as chain buckets on an elevator-hoist lift grain to upper bins. The wheel type has a curious mechanical feature in that the wheel itself has no central hub. Instead, it consists merely of a rim supported by four sets of rollers mounted on an internal framework. The reason for this is that it gets all the driving machinery up near the top of the wheel, enabling a deeper trench to be dug with a smaller wheel than would otherwise be possible. In fact both types have their driving mechanism located at the upper end of the chain, and both also make use of a transverse conveyor belt to carry the excavated material to wagons as fast as it is brought up.

Behind the wheel on the wheel type cf machine is located a bracket-like or L- shaped framework, known as the "shoe."

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