Location Controls

What are Location Controls?

Location controls define where a feature must be located relative to a datum reference frame. They control the position of features like holes, pins, slots, and bosses.

The primary location control is:

Symbol	Name	Controls
⊕	Position	Location of feature's axis or center plane

Note: Concentricity and Symmetry were deprecated in ASME Y14.5-2018 in favor of Position with appropriate modifiers.

True Position

True position is the theoretically exact location of a feature as defined by basic dimensions from datums.

Basic dimensions are shown in boxes and have no tolerance:

         ┌────┐    ┌────┐
         │ 50 │    │ 30 │
         └────┘    └────┘
            │         │
            ▼         ▼
    ════════╬════════════════ Datum B
            ║
            ║    ⊙ ← Hole's true position
            ║
    ════════╬════════════════ Datum A

Position Tolerance

The position tolerance defines a cylindrical (or planar) zone within which the feature's axis must lie:

The Cylindrical Tolerance Zone

For holes and pins, position creates a cylindrical zone:

                  ╭─────╮
    True         │  ⌀   │  ⌀ 0.25 tolerance zone
    Position ──► │  ○   │
                  ╰─────╯
                     │
    Actual axis must lie within this cylinder

Calculating Position Deviation

The position deviation formula:

Position Deviation = 2 × √(ΔX² + ΔY²)

Where:

Bonus Tolerance (MMC/LMC)

When (M) is specified, you get bonus tolerance as the feature departs from MMC:

For a Hole (Internal Feature)

MMC = Smallest hole (most material)
LMC = Largest hole (least material)

Example:
Hole size: ⌀ 10.0 ± 0.2
MMC = 9.8mm (smallest)
LMC = 10.2mm (largest)

Position: ⌀ 0.25 (M)

If actual hole = 10.0mm:
Bonus = 10.0 - 9.8 = 0.2mm
Total position tolerance = 0.25 + 0.2 = 0.45mm

Bonus Tolerance Table

Actual Hole Size	Bonus	Total Position Tolerance
9.8 (MMC)	0	0.25
9.9	0.1	0.35
10.0	0.2	0.45
10.1	0.3	0.55
10.2 (LMC)	0.4	0.65

Position for Hole Patterns

Position is commonly used for bolt hole patterns:

Composite Position Tolerance

For patterns requiring both pattern location AND hole-to-hole relationship:

┌───┬────────────┬────────┬────────┬────────┐
│ ⊕ │ ⌀ 0.50 (M) │ A      │ B      │ C      │  ← Pattern to datums
├───┼────────────┼────────┴────────┴────────┤
│ ⊕ │ ⌀ 0.15 (M) │                          │  ← Hole-to-hole
└───┴────────────┴──────────────────────────┘

Upper segment: Pattern location relative to datums (0.50)
Lower segment: Feature-to-feature relationship (0.15)

Position vs. Concentricity

Characteristic	Position	Concentricity (Deprecated)
What it controls	Axis location	Mass center location
Zone shape	Cylindrical	Cylindrical
Modifiers	Allows MMC/LMC	RFS only
Inspection	Simple	Complex

Recommendation: Always use Position instead of Concentricity.

Key Takeaways

Position controls feature location relative to datum reference frame
Basic dimensions define true position (shown in boxes)
Position tolerance creates a cylindrical zone for axes
MMC modifier provides bonus tolerance as feature departs from MMC
Composite position controls both pattern location and feature-to-feature
Position replaces the deprecated Concentricity and Symmetry

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Next Lesson: Profile Controls - controlling complex shapes and surfaces.