Drafts and tapers allowance
It is not good for a casting to have surfaces whose normal is perpendicular to the direction along which the part will be ejected from the mold.
This can cause the part to stick in the mold and forceful ejection will cause damage to the part (and mold, if the mold is re-usable).
Therefore all such surfaces are tilted by a small angle (between 0.5° and 2°) so as to allow easy ejection. Draft angles on the inner surfaces of the part are higher, since the cast part also shrinks a little bit towards the core during solidification and cooling.
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