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Rh up to the cylinder flange to which it has to be bolted. The accuracy of the work is generally such that no alteration is needed, but it does occasionally happen that in these respects a boiler is slightly out of truth, and a lot of extra chipping and fitting of the expansion angle iron, and heating and setting of the tubeplate flange are then required.

The smokebox is then built up in position. It is made of thin steel sheets riveted together and to the smokebox tubeplate flanges. The front portion is formed of a large angle iron ring, and a plate, in which the smokebox door-hole is formed, is riveted to this ring. The front plate and the sides at the bottom are bolted to flanges on the cylinders. The smokebox must be quite air-tight, for if it draws air through any crevices or through a badly-fitting door, the boiler will not make steam properly, and any incandescent cinders drawn through the tubes will continue to burn in the smokebox and damage the thin plates. The tops of the (inside) cylinders form the floor of the smokebox, and a covering of fire brickwork and cement is placed over them to protect them from corrosion. The blast pipe and steam pipes in the smokebox are then put into position and jointed up to the cylinders. The steam pipe has also to be jointed with a steam tight joint to the T-pipe in the smokebox. The blast pipe is set accurately with a plumb line, since the centre of the top must coincide with the vertical centre line of the chimney, otherwise a