<P> When the pattern is to be removed from the sand mold, there is a possibility that any leading edges may break off, or get damaged in the process . To avoid this, a taper is provided on the pattern, so as to facilitate easy removal of the pattern from the mold, and hence reduce damage to edges . The taper angle provided is called the Draft angle . The value of the draft angle depends upon the complexity of the pattern, the type of molding (hand molding or machine molding), height of the surface, etc . Draft provided on the casting is usually 1 to 3 degrees on external surfaces (5 to 8 internal surfaces). </P> <P> The surface finish obtained in sand castings is generally poor (dimensionally inaccurate), and hence in many cases, the cast product is subjected to machining processes like turning or grinding in order to improve the surface finish . During machining processes, some metal is removed from the piece . To compensate for this, a machining allowance (additional material) should be given in the casting . the amount of finish allowance depends on the material of the casting, size of casting, volume of production, method of molding, and etc...</P> <P> Usually during removal of the pattern from the mold cavity, the pattern is rapped all around the faces, in order to facilitate easy removal . In this process, the final cavity is enlarged . To compensate for this, the pattern dimensions need to be reduced . There are no standard values for this allowance, as it is heavily dependent on the personnel . This allowance is a negative allowance, and a common way of going around this allowance is to increase the draft allowance . Shaking of the pattern causes an enlargement of the mould cavity and results in a bigger casting . </P> <P> During cooling of the mould, stresses developed in the solid metal may induce distortions in the cast . This is more evident when the mould is thinner in width as compared to its length . This can be eliminated by initially distorting the pattern in the opposite direction . </P>

Shake allowance is a positive or negative allowance