Concrete Roads
and Their Construction

126 CONCRETE ROADS tuted where desirable. It must, however, be recognized that the use of any type of caterpillar traction, while it increases the speed of the shovel in operation, makes moving of the shovel from one job to another very much slower than is the case where ordinary traction wheels are used. These shovels are sufficiently light to be used for ordinary street and road work without planking, although most of the traction wheels are so arranged that cleats can be attached when necessary. Several of these machines, in addition to the customary fea- tures of steam-navvies, are equipped with special devices for use in shallow cuttings and for automatic levelling and grading work. While these navvies are generally classed as “ one man ” machines, it is usually desirable to provide an assistant to take-care of the firing of the boiler, keeping up the coal and water supply, and generally assisting in operation. One or two pit men are needed, depending on the type of machine, speed of the work, and the care which it is necessary to give in cleaning and levelling up. It must be recognized that the output from these navvies depends almost altogether on the skill of the operator. A working speed of from two to three dippers per minute canjbe obtained by the average operator, although skilled men can obtain from four to five dippers per minute with the same shovel working under similar conditions. Some navvies of the type mentioned above are the Erie Shovels, manufactured by the Ball Engine Company of Erie, Pennsylvania, and now sold in this country by Gaston Limited and by William Muirhead, Macdonald Wilson & Co. Ltd., the Thew Shovel, manufactured by the Thew Shovel Company, Lorain, Ohio, sold in this country by the Allied Machinery Company, Ltd., and the shovels manufactured by the Bucyrus Company of Milwaukee, Wisconsin, sold in England by Messrs. George F. West & Co. Cranes and Grabs.—For lifting large quantities of loose materials, such as sand, aggregate and tipped earth, it is sometimes cheaper to use a crane and grab than a steam shovel. A firm of crane and grab manufacturers in this country is Priestman Bros., Ltd., Hull, one of whose machines is shown in Fig. 79. A modification of the Erie shovel in which a grab is used instead of a shovel is shown in Fig. 82. A similar ci’ane and grab, made