Patterns can be defined as any model, built in such a way that it can be used to form an impression called "mold" in moist sand or other suitable materials. There is also a define as a workpiece replica which will be produced by casting techniques, with tolerance / suaian size according to the calculation of casting. The size of the pattern, usually larger than the workpiece.
To make a casting object is required liquid metal and mold, where the molten metal is poured into the mold cavity, then after the metal freezes and the temperature is sufficient for dismantling is done the dismantling of the mold. In the manufacture of molds in the case of making the cavities of prints are meticulous in size, with various forms required a tool called a pattern.
As castings shrink in freezing and cooling time, the pattern-makers need to use a previously extended retractable ruler as much as additional depreciation on the pattern size. The amount of shrinkage is often not isotropic according to: casting material, shape, place, thick castings, or core size and strength. Then considering the shape sometimes the shrinking ruler is changed in the direction of upright or horizontal. Therefore the requirements should be written on the drawing for the casting.
