What one degree of draft buys you

A moulded part shrinks onto the core as it cools, gripping it. The ejectors then have to break that grip and push the part off. Draft — a slight taper on every face that runs parallel to the direction the tool opens — is what turns that from a scrape into a release.

• One degree per side is the common starting point for a smooth surface.
• Half a degree is workable on shallow features in a well-polished tool.
• Deep ribs and tall cores want 1.5 to 2 degrees, because the contact area is larger.
• A textured surface needs roughly one extra degree for every 0.001 in of texture depth.
• Draft the inside of ribs and bosses as well, not only the outside walls.

What no draft actually costs

A part that does not want to release needs higher ejection force, which prints ejector pin marks into the surface and can stress-whiten or crack the part at the pin. It also needs to be cooler and stiffer before it can be pushed, which lengthens the cycle. And every shot drags the part across the steel, so the tool polishes, then wears, then needs work. A dimension held by removing draft is a dimension paid for on every part, forever.