When a molded part cools it shrinks onto the core. If its walls are parallel to the opening direction, the ejector pins have to scrape it off, leaving drag marks or cracking thin ribs. Draft is the small taper that prevents this.
How much draft?
- 1° on most smooth walls.
- 2° or more on tall walls and ribs.
- Add about 1° for every 0.025 mm of texture depth.
Adding draft in SolidWorks
Use the Draft feature with the parting line or a neutral plane that matches the mold opening. Then run Draft Analysis: green faces release, red faces need more draft, and yellow faces straddle the parting line.
Draft early, not last
Draft changes wall thickness and fillets. Add it right after the main body, before shells and fillets, so later features follow the tapered faces instead of fighting them.
