Afterwards place a long straight-edge across the three and level the boiler longitudinally, and mark along the casing for the expansion bracket, the holes for which have been drilled at the same time as the stay holes. Supposing the line for the edge of the bracket is, say, 1/16 inch out from the required position, it is passed; but if more, the boiler must be canted over, whichever way required, until the error is divided, this requiring to be done in something like 2 per cent, of the total boilers made. The brackets, Fig. 38, are steel castings, with the holes for clearing the stay heads cast in. They are bolted to the casing through these holes, and then the foreman tries them over, marking them and the casing with trammels for the riveter to work to, who notes that they do not shift in riveting. Four holes are marked from the inside of the casing, and the rest are drilled through a jacket. Having marked the expansion bracket, the longitudinal centre hue along the barrel has to be marked, using the above 2 feet 8 inch gauge, only the reverse way. Lines are thrown over the barrel, and the straight-edge M brought up to them, the gauge otherwise would cant over, and consequently not show the exact length. Each end of each section is then marked by scribing in between with shorter and more convenient straight-edges, at the same time carrying this hue to the weldless ring. The smoke-box tube-plate is then cramped on, the centre line of the plate to the centre line of the weldless ring. A straight-edge is then held upon the bottom edge of the plate, which has been previously planed. It is then levelled, and the rivet holes marked with a ring punch.

Fig. 38.

The dome is formed from an oblong plate of best iron or mild steel, welded at the seams and flanged at the bottom, with an angle iron ring at the top, and fitted with a wrought-iron or mild steel cover. The flanges of the dome and cover are faced, so that steam-tight joints are made. It is marked from template and sheared, allowing from « inch to ¾ inch for welding the contour to form the flange for riveting to the boiler, and four holes being punched. The inside edge is planed bevel for the scarf, the plate is then bent to radius, and rivets put in to hold it together whilst welding. After fixing the welding block and stand, with its platform for the smith and strikers, the porter bar is clamped to the dome shell. Fig. 39. If there is too much lap for the scarf, the ring after warming is paened on the outside, and if too little, on the inside, until the required lap is obtained. The first is a nice wash heat, the weld being shut about 6 or 8 inches from one end, a fuller being used to bring the outside lap upon the bevel edge of the inside, the scarf being off. The welds are generally "shut" at two heats, applied alternately to a forward portion and a hind one, but if not properly welded up a third is required, the straightness and radius of the dome being watched throughout.

Great care is taken with the heats, this being necessary, because the outside lap heats up quicker than the inside; although a fire-brick is placed over the portion to be shut, which retains the heat well. After the seam has been shut along its whole length, the end to be flanged has a piece of bar iron welded across the joint; after this, it is never known to open during flanging.

Dome Template.

Fig. 39.

The flange is formed in a block, Figs. 40, 41, 42, about one-third to one-quarter at a time, after which it is set perfectly right in relation to its axis and sides, using the gauges upon a block similar to Fig. 43. The dome is then placed upon the template, Fig. 43, and squared up from the surface plate; four holes being set out and the rest drilled through a jacket. For this purpose the dome is fixed upon a frame on an axis, in order to get the holes at right angles with the flange.

The seating for the cover may be flanged, or formed from an angle iron, which is bent to radius on a block at the furnace, the ends being bevelled to form a scarf; and in welding up, a piece of square iron is let in at a welding heat, bent over upon the flat, and completely shut, the same precautions being taken as to heating. All cases are finished accurately. It is then skimmed up for entering the dome, which is warmed and shrunk on. The two are drilled together whilst resting upon a roller frame, and afterwards riveted up. It is then cramped to a block in the lathe, squared to the face plate, and the face of the angle turned up; afterwards drilled, tapped with a lightning tapper, and riveted to the boiler. It is found by following out the above treatment, that although the dome has never been near the barrel before, it is almost absolutely correct, certainly sufficient for all practical purposes. The covers are dished at the steam hammer, the tup and anvil being convex and concave, and finished by turning the faces and edges.

Fig. 40.

Fig. 41.

Fig. 42.

Dome Gauges.

The safety valve seating is made similar to the angle ring in the dome, using the required section of best iron or mild steel, and flanged to the radius of the outside fire-box shell; now, however, speaking generally, a steel casting is used. The holes are marked from a template, similar to the dome template, Fig. 43, the scriber D being used to set out how much must he turned from the seating. Four holes are marked, and the rest drilled through the template or jacket.