Profile of a surface is a GD&T control that keeps every point of a surface within a 3D band around its true shape, defined by basic dimensions or CAD. With datums it controls size, form, orientation and location of the surface at once, which makes it the most versatile symbol in the system.
Profile of a surface wraps the exact, nominal surface in a skin of uniform thickness and requires the real surface to stay inside it. It works on flat faces, curved panels, castings, molded parts and freeform shapes.
Without datums, it controls form only, like a flatness that works on any shape. With a primary datum it adds orientation; with a full datum reference frame it adds location, replacing a page of plus-or-minus dimensions with one frame. This is why many modern drawings use a general note such as "all unspecified surfaces: profile 0.5 A B C".
Because profile controls location, it is also one of the replacements recommended where older drawings used concentricity or symmetry.
The zone is the volume between two surfaces that follow the true profile at a constant distance apart, equal to the tolerance. It is equally split either side by default; the unequally disposed modifier moves it.
With datums the zone is fixed in the datum reference frame. With no datums it may float to fit, so only the shape is controlled.
Datums are optional. No datums gives a pure form control; adding datums adds orientation and location. Most uses reference a full datum reference frame.
| Modifier | With profile of a surface |
|---|---|
| MMC or LMC on the tolerance | Not allowed. The control applies to a surface. |
| Datum modifiers (MMB/LMB) | Allowed on datum features of size. |
| Unequally disposed (U) | Places the band unevenly, for example all outside the nominal for a casting with stock to remove. |
| All around / all over | Extends the callout to every surface around the view or over the whole part. |
| Dynamic profile | A triangle modifier that refines form without controlling size, used under a looser profile. |
Example: a die-cast cover with its outer surface defined by the CAD model
Result: Both are inside ±0.2 mm, so the surface passes. A point at +0.23 mm would fail even though the 0.4 band is "bigger", because the band is split equally.
Every GD&T symbol page: GD&T symbols chart
Form alone when used without datums. With datums it also controls orientation and location, and for closed shapes it also limits size.
Profile of a line is an open arc; profile of a surface is the same arc closed with a straight line at the bottom.
By default yes, split equally either side of the true profile. The unequally disposed modifier (a circled U) shifts the split.
Yes. A profile with a full datum reference frame often replaces many coordinate dimensions with one frame, as long as the geometry is defined by basic dimensions or CAD.
Not on its tolerance value. Datum references that are features of size can carry MMB or LMB modifiers.
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