While it is the general practice to use flasks and patterns for the purpose of making moulds, it is sometimes possible to do the work without either or with only one. Where flasks are not used the mould is prepared in the sand forming the floor of the foundry.' This work is usually confined to flat plates where the upper surface is large and smooth. As an example of this class of work, take a rubbing plate 6 feet square and 6 inches thick. This will weigh a little more than four tons. A place on the floor is selected that can be reached by a crane. The floor is first rammed hard and evenly over a surface of about 8½ feet square. The ramming is done at a level of about 6 inches below the floor surface in a hole excavated for the purpose. The bed must then be leveled over its whole area. This is done by setting straight edges in the sand 8 feet apart. The straight edges are to be set perfectly level and of the same height. It is done with a spirit level as shown. The four stakes a a a a (Fig, 54) are driven into the ground at the proper distances as shown. Upon these the straight edges A A are leveled by spirit levels b b. They are, in turn, brought to the same height by the spirit level set on the straight edge B. When the two upper edges d d of the straight edges A A are adjusted, the floor is scraped off with the straight edge B. It is then sleeked smooth and the pattern laid on the same.
In this case the pattern may be a square frame as shown in Fig. 55. The sand is then rammed about the outside of the pattern, the gates cut and the pattern drawn. This leaves an open mould as shown in Fig. 56. In pouring, the metal must not be run directly into the mould. The fall from the ladle would cut away the sand. It is therefore poured into basins and allowed to flow into the mould through the gates a a cut in the sand at the sides.