Upright tubular boilers are generally used to supply steam for concrete mixers and hoists operated by steam engines, when they are isolated. For the smaller sizes of mixers, the boilers are on the same frame as the engine and mixer. Fig. 128 shows a McKelvey mixer, engine, and boiler mounted on the same frame. In a similar manner the boiler is often fastened to the same frame as the hoisting engine. This arrangement cannot be used for the larger sizes of mixers and hoists, as they are too heavy to be handled conveniently.

When it is possible, the mixer and hoists should be supplied with steam from one centrally located boiler. A portable boiler is then generally used. 345. Wood= working Plant. A portable woodworking plant can very often be used to advantage in shaping the lumber for the forms when a large building is to be erected. The plant can be set near the site of the building to be erected, and the woodworking done there. The machinery for such a plant should consist of a planer adapted for surfacing lumber on three sides, a rip saw, a crosscut circular saw; and in some cases a band saw can be used to advantage. Usually, the difference in cost between surfaced and unsurfaced lumber is so small that the lumber could not be surfaced in a plant of this kind, for the difference in cost; but perhaps it would be more uniform in thickness. In such a plant the rip saw and the crosscut saw would be found to be the most useful; and if reasonable care is taken, this machinery will soon pay for itself. It is often difficult to get work done at a planing mill when it is wanted; and if a contractor has his own woodworking machinery, he will be independent of any planing mill. A plant of this kind can be operated by a steam or gasoline engine or an electric motor.

Fig. 143. Automatic Loading Bucket

Fig. 143. Automatic Loading Bucket.

Fig. 144. Koehring Concrete Cart.

Fig. 144. "Koehring" Concrete Cart.