The size of the investment casting are high precision and low surface roughness, so most of the surface can not machining or less processing, machining allowance can not or less left.
However the machining allowance for how much still depends on the casting processing method, and the size of the processed surface, and the casting structure and other factors.
Such as on the casting surface blowhole, slag is more, the surface sand holes and the side is better, the following should take larger machining allowance.
Big casting easy to deformation, and the large surface castings, due to the low precision casting geometry, so the machining allowance have thrown some;
Carbon steel casting because of the decarburization layer appears unavoidably, the machining allowance should be decarburization layer thickness. Machining allowance is also related to machining methods.
In general,where set the riser system, its machining allowance for 2 ~ 4 mm other surface processing is for 0.5 ~1.5mm.