⌒ Profile of a line
Profile of a line · Perfil · ISO 1101 + ASME Y14.5
Example in plan
How to interpret it
The profile of the indicated 2D line or outline must stay within a 0.1 mm band around the theoretical geometry defined by basic dimensions, relative to datum A.
What controls
Controls the form of a line (the outline seen in a specific cross section) relative to the theoretical profile defined by basic dimensions or by the CAD model, without comparing the whole 3D surface (that is what profile of a surface is for). The tolerance zone is a band that follows the theoretical outline, with a width equal to the stated value; it can be split equally on both sides of the nominal profile or unequally disposed (with the ⊕/⊖ modifier) toward one side.
How to verify
An optical comparator (profile projector) overlays the magnified actual silhouette on a chart or reticle showing the theoretical outline and its tolerance band. A 2D laser scanner or a CMM probing points along the section gives numerical results that can be compared directly with the CAD model. Always establish which specific section is being checked: profile of a line is valid only at that section and does not guarantee the rest of the outline if the part changes shape along its length.
tolerance zone
Band of constant width around the theoretical outline at that section; it can be equal or unequally disposed (⊕/⊖).
Datums and notes
It can be used without datums, in which case it controls only the form of the outline, or with datums, in which case it also fixes its location and orientation relative to the part. Always check which of the two cases applies: the same symbol and the same value mean very different things.
Workshop guideline values
- General
- 0.1–0.3 mm on 2D contours in general machining.
- Accuracy
- 0.03–0.08 mm on cams or tight functional profiles.
- High precision
- 0.01–0.03 mm on airfoils or precision cams.
Guidance only: the drawing's value always wins.
Common mistakes when interpreting it
- Checking only one or two points on the outline and extrapolating the rest: profile of a line requires covering the entire section, since an irregular stepover can leave specific areas out of tolerance even when the rest is fine.
- Not checking whether the tolerance is bilateral or unilateral (with ⊕/⊖): a profile shifted to one side of nominal can be misread as a failure if it is assumed to be equally disposed by default.
How to get it in the workshop / if it comes out of tolerance
Shows up on airfoils, cams and 2D contours. It can be unilateral or bilateral depending on the value and modifiers.
If the outline comes out of profile, first check tool wear in curved areas (a ball end mill loses effective diameter as the tip wears) and the stepover in the CAM program: too wide a stepover leaves facets that exceed the profile tolerance even though the CAM "says" it is fine. On thin profiles, vibration from tool overhang also pulls the actual line away from the outline.
Related symbols
Other symbols in Profile
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