Why is Profile of a line used?
An extruded rail can meet a few linear dimensions while its working edge wanders between them.
PROFILE CONTROL / GD&T SYMBOL GUIDE
PROFILE OF A LINE
Profile of a line limits each specified two-dimensional cross-section of a contour. With datum A, the zone is oriented or located as the frame and basic geometry require.
INTERACTIVE APPLICATION
GD&T profile of a line example: extruded rail contour
NO SEPARATE CONTROL
The rail edge can wander between checked points
- No separate profile of a line requirement is stated for this extruded rail contour.
Limitations
- An extruded rail can meet a few linear dimensions while its working edge wanders between them.
- Mating contact may vary along the edge.
PROFILE OF A LINE CONTROL
Each section follows the specified contour
- The orange surface contour must stay inside the 0.20-wide zone at every specified cross-section.
- The profile frame references datum A; basic geometry defines the intended contour.
Advantages
- Cross-sections better follow the intended mating contour.
- The drawing states the intended requirement for inspection and assembly.
Where is Profile of a line used?
Extruded rails, cam edges and repeated cross-sections of formed parts.
How is Profile of a line used?
Identify the controlled contour and section direction. Define the true profile with basic geometry and attach the frame to the contour; datum A is used in this example.
The double-ended arrow shows the total 0.20 zone width between the profile boundaries. The orange line is the actual surface contour at one specified cross-section.
How it is used
Identify the controlled contour and section direction. Define the true profile with basic geometry and attach the frame to the contour; datum A is used in this example.
How to read the annotation
Read the profile of a line symbol first, then the 0.20 tolerance in the drawing units. Datum A establishes the referenced orientation or location. Follow the frame leader to the controlled extruded rail contour.
Commonly defined variable values
The controlling value is a tolerance-zone width, not a universal process grade. For this profile of a line example, the drawing states the controlled feature and applicable extent.
Scroll the table sideways to see every column.
| Application | Illustrative starting value | Example feature | Notes / caution |
|---|---|---|---|
| Extruded Rail Contour | 0.20 mm | extruded rail contour | Illustrative only; define the sections and full profile extent. |
These are planning examples, not universal rules or guaranteed process capabilities. Set the actual tolerance from function, size, length, process capability, inspection method and the standard specified on the drawing.
Line profile vs surface profile: which one to use?
Profile of a line controls individual cross-sectional line elements. Use it when the requirement is checked section by section, such as an extruded rail contour.
Profile of a surface controls the whole 3D surface. Use it when the entire surface must meet one specified zone.
Explore profile of a surface →How is profile of a line measured in real life?
Establish datum A first. Measure the indicated feature and compare it with the requirement shown on the drawing.
- CMM or profile scan: Sample each specified section and compare it with the basic contour.
- Optical comparator: Check an accessible section against a datum-aligned overlay.
ASME Y14.5-2018 (R2024)
ASME Y14.5 distinguishes line profile from full-surface profile; datum references control the relationship shown in the frame.
ASME Y14.5 edition reference. Examples are learning schematics; use the complete requirements on the drawing.
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