Orientation Tolerances and Controls
Orientation relative to a datum
Orientation controls are perpendicularity, parallelism, and angularity. They limit the angle of a feature relative to a datum but not its location. The tolerance zone is oriented to the datum and floats in translation unless a location control is also applied.
Concepts to command
Know the tolerance zone shapes: two parallel planes for surfaces, a cylinder for axes, and the relationship to basic dimensions for angularity. Understand that orientation controls always require a datum. Know how orientation interacts with Rule #1 and with size: for a feature of size, the orientation tolerance plus size defines a virtual condition boundary. Understand the difference between orientation of a surface (flatness-like zone tilted to datum) and orientation of an axis (cylindrical zone).
Traps that appear in questions
- Orientation does not control location; a hole perpendicular to a datum can still be anywhere on the surface unless position is also specified.
- Angularity requires a basic angle; a toleranced angle is not permitted with an angularity control.
- Applying perpendicularity to a feature of size at MMC creates a boundary that may be tighter than the size tolerance allows; check for conflict.
- Confusing parallelism (orientation) with profile (which can control both form and orientation).
Rule of thumb
Orientation = angle control only. If the question asks where the feature is located, orientation alone cannot answer it; you need position, profile, or a linear dimension.
Worked example
A hole Ø8.0 ±0.1 perpendicularity Ø0.2 to datum A: the hole axis must lie within a Ø0.2 cylinder oriented perpendicular to A, but the cylinder can translate anywhere on the surface. Add position to locate it.