Profile Tolerances and Controls
The most versatile control
Profile of a surface and profile of a line control form, orientation, location, and size (when the profile is a closed shape or the size is basic). Profile of a surface uses a tolerance zone of two parallel surfaces offset from the true profile; profile of a line uses two parallel lines in each cross-section.
Concepts to command
Know that profile requires basic dimensions to define the true profile and usually a datum reference frame. Understand bilateral (default, equally disposed) versus unilateral profile (all tolerance on one side, indicated by a phantom line or a note). Know composite profile (pattern location versus feature-relating). Know that profile can control a feature of size when the size is basic, and that profile applied to a feature of size at MMC creates a boundary.
Traps that appear in questions
- Assuming profile is always bilateral; the default is bilateral but unilateral must be explicitly indicated.
- Forgetting that profile of a surface can control size when the size is basic, unlike other controls.
- Confusing profile of a line (cross-section only) with profile of a surface (full 3D).
- Applying profile without basic dimensions to define the true profile.
Rule of thumb
Profile is the only control that can simultaneously control form, orientation, location, and size. If a question asks for a single control that does everything, the answer is usually profile.
Worked example
A curved surface defined by basic radii and located by basic dimensions, with profile of a surface 0.5 to A|B|C: the actual surface must lie between two surfaces 0.5 apart, equally disposed about the true profile, oriented and located by the DRF.