Draft is generally provided to make a clearance between the pattern and the mould during pattern extraction.
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It is not necessary to avoid any sharp internal corners from casting design, as it causes very negligible problems.
Lack of filleting of sharp corners in the casting design can cause hot spots in the casting.
Sharp corners in casting design may cause defects in the casting but it helps in strengthening of pattern material.
Sharp corners in the casting design also produce the problem of sand inclusion in the castings.
In horizontally parted moulds, a draft is required for vertical as well as for horizontal surfaces of a pattern.
In casting design, concave junctions are generally added to avoid the effect of sharp corners in the casting.
In pattern fillets, the size of a fillet is usually determined by its width.
A very large fillet in casting design also may cause shrinkage defects in the casting.
Sharp internal corner of the casting also causes the misrun defect in the casting.
To avoid sharp external corners in casting design, rounding of external edges is done in pattern making that termed as radii.
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