GD&T Fundamentals
Lesson 7 of 10 12 min

Profile Controls

What are Profile Controls?

Profile controls define the allowable deviation of a surface from its true (theoretical) profile. They are the most versatile GD&T controls, capable of controlling form, orientation, and location simultaneously.

There are two profile controls:

SymbolNameControls
⌓Profile of a Line2D cross-sectional shape
⌔Profile of a SurfaceEntire 3D surface

Profile of a Line (⌓)

Definition: Controls individual line elements of a surface. Each cross-section must lie within the tolerance zone. 
FCF: ┌───┬──────┐
     │ ⌓ │ 0.2  │
     └───┴──────┘

           ╭──────────╮
          ╱    0.2     ╲  Tolerance zone follows
         │   ~~~~~~~~   │  theoretical profile
          ╲            ╱
           ╰──────────╯
Use Case: Extrusions, sheet metal bends, features where manufacturing varies along length.

Profile of a Surface (⌔)

Definition: Controls the entire surface simultaneously. The complete surface must lie within a 3D tolerance zone. 
FCF: ┌───┬──────┬────────┐
     │ ⌔ │ 0.5  │ A      │
     └───┴──────┴────────┘

    The entire surface must lie between
    two surfaces offset from the true profile
Use Case: Complex contours, aerodynamic surfaces, mold cavities.

Profile Zone Types

Bilateral Equal (Default)

The tolerance zone is split equally on both sides of the true profile:

Tolerance: 0.4

         ═══════ +0.2 (outside true profile)
    ─────────── True Profile
         ═══════ -0.2 (inside true profile)

Bilateral Unequal

The zone is split unequally, specified by a note:

Tolerance: 0.4 (0.1 outside, 0.3 inside)

         ═══════ +0.1
    ─────────── True Profile
         ═══════ -0.3

Notation: 0.4 ⌔ A with note "0.3 INSIDE"

Unilateral

The entire tolerance is on one side of true profile:

Tolerance: 0.4 (all outside)

         ═══════ +0.4
    ─────────── True Profile
         (no zone inside)

Notation: Uses the ⓤ (unilateral) symbol or arrow indicator

Profile With and Without Datums

Without Datums (Form Only)

Controls only the shape of the surface:

┌───┬──────┐
│ ⌔ │ 0.5  │
└───┴──────┘

The profile can float and rotate—only shape matters.

With Datums (Form + Orientation + Location)

Controls shape AND position relative to datums:

┌───┬──────┬────────┬────────┬────────┐
│ ⌔ │ 0.5  │ A      │ B      │ C      │
└───┴──────┴────────┴────────┴────────┘

The profile must be located where shown relative to the datum reference frame.

Composite Profile Tolerance

Similar to composite position, controls both overall location and local shape:

┌───┬──────┬────────┬────────┬────────┐
│ ⌔ │ 1.0  │ A      │ B      │ C      │  ← Location to datums
├───┼──────┼────────┴────────┴────────┤
│ ⌔ │ 0.2  │                          │  ← Local refinement
└───┴──────┴──────────────────────────┘
  • Upper segment: Profile located within 1.0 of datums
  • Lower segment: Local form refined to 0.2

Profile Applications

Complex Curves

Profile is ideal for curves defined by equations, splines, or CAD models:

    ╭─────────╮
   ╱           ╲
  │  Airfoil   │  Profile tolerance follows
   ╲           ╱  the theoretical curve
    ╰─────────╯

Coplanar Surfaces

Multiple surfaces that must be flush:

Profile connects multiple surfaces
into one controlled zone:

    ┌─────┐     ┌─────┐
════╧═════╧═════╧═════╧════
     All surfaces in profile

All-Around Profile

The circle symbol indicates profile applies all around:

     ○
     │
┌───┬──────┬────────┐
│ ⌔ │ 0.5  │ A      │
└───┴──────┴────────┘

Applied all around the part outline

Profile vs. Other Controls

ControlBest For
FlatnessSimple flat surfaces
ProfileComplex shapes, curved surfaces
PositionLocating features (holes, pins)
ProfileLocating irregular features
Modern Trend: Profile is increasingly used as a "universal" control because it can replace form, orientation, and location controls in many cases.

Key Takeaways

  • Profile of a Line: controls 2D cross-sections
  • Profile of a Surface: controls entire 3D surface
  • Default is bilateral equal (split 50/50)
  • Unequal or unilateral distribution specified by notes
  • Without datums: form only
  • With datums: form + orientation + location
  • Profile is the most versatile GD&T control

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Next Lesson: Runout Controls - controlling surface variation during rotation.
Location Controls