In an article in MEW 181 I described my set up for aluminium casting and showed how castings can be made using the lost foam method. In the lost foam method of casting a pattern is made in expanded polystyrene. A sprue (or sprues) of expanded polystyrene is attached to the pattern and the whole then buried in loose dry sand with the sprue protruding above the sand. Molten aluminium is then poured down onto the sprue and this melts and replaces the polystyrene yielding a casting the same shape as the pattern. This procedure is ideal for one off castings. The polystyrene pattern can be shaped by various means: it can be carved using a craft knife, milled sanded etc. However the easiest and most accurate method of cutting expanded polystyrene is to use a hot wire cutter. With a hot wire cutter it is possible to cut sheets, blocks, cylinders, rings etc. It can also be used to cut more complex shapes using a cardboard template. In this article I shall describe the construction of a small hotwire cutter, together with accessories, and also explain the techniques that can be used to build complex patterns.
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