Draft Angle in Injection Molding

Draft is a small taper applied to surfaces that move relative to the mold during ejection. It is one of the simplest DFM features to add early and one of the most expensive to discover late.

What draft angle means

Draft angle is the angular taper between a nominally straight wall and the mold pull direction. Instead of maintaining exactly the same cross-section along the full depth, the wall opens slightly so contact with the tool reduces as the part moves.

Why molded parts need draft

Plastic shrinks as it cools and can grip cores or textured steel. A zero-draft wall may slide against the tool over its full depth during ejection, increasing friction, drag marks and ejector load. Draft helps the part release progressively.

How much draft to use

There is no single correct value. Many designers start around fractions of a degree to a few degrees for ordinary untextured surfaces, but the right value depends on material, depth, shrinkage, texture, tool polish and whether the surface is core- or cavity-side. Confirm important surfaces with the molder.

Texture increases the need

Texture creates mechanical engagement with the tool surface, so deeper or more aggressive textures usually need additional draft. Cosmetic texture specifications should therefore be considered before the exterior shape is frozen.

Core versus cavity

A plastic part often shrinks onto the core as it cools, which is useful because it helps keep the part on the ejector side. Draft direction must follow the actual tool split and ejection strategy—not simply the CAD model’s global axis.

Use CAD draft analysis

Define the pull direction, run a color draft analysis and inspect every face that slides relative to tool steel. Review ribs, bosses, shutoffs and deep pockets separately because their local tooling direction may differ.

Calculate the dimensional effect

Draft changes dimensions with depth. Use the DIVE-LD Draft Angle Calculator to estimate the one-side offset and total size change before committing to a taper.