It is not a specification and care should be taken to reach agreement on what tolerances is required. Close cooperation between the customer's design engineers and the foundry's engineer is essential to optimize the casting design. The rigidity of a section often governs the minimum thickness to which a section can be designed. There are cases, however, when a very thin section will suffice, depending upon strength and rigidity calculations, and when castability becomes the governing factor. In these cases it is necessary that a limit of minimum section thickness per length be adopted in order that liquid metal will completely fill the mold cavity in these thinner sections.
Molten steel cools rapidly as it enters a mold.
In a thin section, close to the gate, which delivers the hot metal, the mold will fill readily. At a distance from the gate, the metal may be too cold to fill the same thin section. Draft Draft is the amount of taper or the angle, which must be allowed, on all vertical faces of a pattern to permit its removal from the sand mold without tearing the mold walls. Draft should be added to the design dimensions while maintaining minimum metal thickness. Regardless of the type of pattern equipment used, draft must be considered in all casting designs.