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A plastic part can be perfect in CAD and still be difficult to remove from the mold. One of the first things to check is draft angle.
What Draft Does
Draft slightly tapers a molded wall so the part can separate from the mold without excessive rubbing or damage.
Why Surface Texture Changes the Requirement
Textured surfaces generally need more draft than smooth surfaces because the texture can resist release. Deep walls may also require more consideration.
Draft Direction
Draft should be applied relative to the tooling direction. That means the designer must understand the likely mold opening direction before finalizing important external and internal walls.
Common Mistake
Designers sometimes add draft at the end, after every feature has been created. This can create broken references and unexpected geometry. Add major draft requirements early.
DFM Review
Review draft together with parting line, ejection, ribs, bosses and wall thickness. These features interact with each other.
Keep learning: Explore more practical engineering articles in the GetCADFile Design Guide.