130 FOUNDRY WORK and removed in sections, the pattern is unscrewed and taken away, leaving the core to be removed. An advantage of this method over the making of a separate pattern and core box is that the correct thicknesses are ensured. But the real reason for the adoption of the method is economy of timber and pattern-maker's time. It is reserved therefore for the larger castings. Loam Patterns.—These, swept in loam, are used instead of those made of wood, to be rammed in moulds of green or dry sand. This is a rather large and important section of foundry work, the object being, as in loam moulding, to save the prohibitive cost of complete patterns of wood. It includes symmetrical work, revolved against the profiled edge of a board fixed on the core trestles, and non-symmetrical articles, formed as half pat- terns with strickles, the longitudinal movements of which are controlled by guide irons, or by the edges of contour plates on which the pattern halves Fig. 27.—Pipe made in Loam A, Guide iron. B, Core grids, c, Core. D, Strickle. E, Mould with core and its chaplets. are swept. The longitudinal shapes are determined by the character of the castings required. They may have regular or irregular curves, or curves combined with straight portions. Instead of using loam patterns, it is often cheaper to make a rough skeleton pattern of wood, with outline ribs, fill the spaces with sand, and ram it in the mould. Fig. 21 shows a skeleton pattern for a pipe bend as sent from the pattern-shop, and fig. 22 one for an S-pipe, having the spaces filled with sand. Figs. 23 to 26 illustrate the making of a pattern, and core for a loam bend. A is the guide iron, set with weights, B is a slender body of loam which forms the vent channel of the core, E, a part of which, D, is seen roughly daubed on the grid c in fig. 24, with its vents, and which is com- pleted in fig. 25. In fig. 26 the pattern "thickness" F, corresponding with the thickness of metal in the casting, has been laid on, and the standard iron pattern socket G and spigot H set, completing the half pattern. After the pattern has been moulded, the thickness is stripped off, leaving the core ready, when blackened, for insertion. In fig. 27 the core strickle, controlled by the guide iron, is seen bridging the core, and the mould is shown to the right, with the core inserted.