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18 continuation of the boiler barrel. This circular portion is produced by means of the plate bending rolls.

Assembling the Boiler. The boiler barrel is attached to the smokebox tube-plate by means of a continuous weldless angle iron ring G (Fig. 2). This is faced and bored in a large lathe or on a boring mill to fit over the end of the circular barrel plate, on to which it is shrunk by being heated slightly so that it expands. When put into place it contracts and grips the barrel plate, to which it is riveted all round the circumference.

The foundation ring H at the bottom of the firebox (Fig. 2) is a steel casting or forging of rectangular shape, the sides of which must be perfectly “square,” as it has to fit accurately between the inner copper firebox and the firebox outer shell or casing. It is machined and ground to accurate dimensions, the rivet-holes marked off and drilled, and then it is fitted to the firebox shell.

The whole of the plates and parts are then put together, and temporarily held in place by bolts through some of the rivet-holes. The structure has to be levelled carefully, so that the different plates are “square” and in line with one another. Careful measurements are made to see that the parts come together in accordance with the drawings or templates, and straightedges are used to test the alignment and “squareness.” When this is correct the riveting is done, except