The first thing to consider when designing a part or modifying an existing design to be cast is the orientation of the part within the mold. This is defined as the direction in which the two halves of the mold separate. When the two halves of a mold move apart to reveal the casting within, they will move in exactly opposite directions along a vertical direction vector. This is the “pull direction”..

The parting line is defined where the two mold halves come together to define the part cavity. This can be seen on most cast or molded parts as a faint line of extra material, “flash”, running all the way around the part. This line is not necessarily confined to a flat plane where the mold halves meet but can be multi-level or compound curves that may move from one half of the mold to the other. However, a flat parting line is preferred whenever possible. Often times the parting line will lie on existing edges of the parts features. A parting line usually becomes quite apparent when considering draft requirements.

When the mold separates along the vertical pull direction, all surfaces which are parallel to this direction vector must be angled away from this imaginary line by at least the specified “draft” requirement. This means that all features of the part must get smaller as they protrude into the mold cavity based on the draft angle. The idea is that the part can be easily removed when the mold separates. When it comes to draft angle, more is better! ZCastings requires at least 3 degrees of draft for most surfaces.