The cost of production is reduced by the use of a match plate on a machine. The rapidity with which the molds can be produced and the possibility of producing castings which require the minimum of machining, lowers the cost. Machine-work in finishing is always a costly process.
In recent years the molding machine has been improved so that at the present time very large castings are produced by it. Of course, its use is only possible or profitable for large-scale production, as the machines for large work, with their patterns, are very expensive.
A large machine of this type is the stripping plate machine in the operation of which the sand is rammed by hand and the pattern drawn down through a metal plate which supports the sand and prevents breaking. By this method, castings can be produced close to uniform size.
When a pattern is rapped to loosen it in the sand before drawing, it is impossible to produce castings of uniform size, as the rapping is left to the molder's judgment. Rapping a long and narrow pattern results in making a casting longer than the pattern unless great care is taken. Such a pattern moves endwise easily because of its narrowness, but moves sidewise very little because its greater surface is not so easily moved. A casting of this kind is often found to be wider on one end because of carelessness in rapping.