Design Nomenclature / Form & Geometry
Draft angle
Also called draft, taper, release angle
The taper given to a face so a part can leave a mould or a die along the pull direction — measured from that direction, not from the face. One to two degrees suits smooth plastic; three or more is needed on textured surfaces, because the texture's depth carries its own undercut. Zero draft drags and scores the part.
In practice
'Undercut' is the failure case: any face with negative draft relative to the pull, requiring a side action or a different process. Draft-analysis shading is a per-face dot product against the pull vector and nothing more.