Runout Controls

What are Runout Controls?

There are two runout controls:

The Inspection Setup

Runout is inspected by:

• Mounting the part on the datum axis (using centers, a mandrel, or V-blocks)
• Rotating the part 360°
• Measuring surface variation with a dial indicator

            Dial Indicator
                 │
                 ▼
    ╔═══════════════════════╗
    ║     Part rotates      ║
    ║    ◄──── 360° ────►   ║
    ╚═══════════════════════╝
              │
        Datum Axis A

1. Circular Runout (↗)

FCF: ┌────┬──────┬────────┐
     │ ↗  │ 0.05 │ A      │
     └────┴──────┴────────┘

How It Works

At each cross-section, the surface variation (FIM - Full Indicator Movement) during one full rotation must be within tolerance:

    Section 1 ──►│    FIM ≤ 0.05
    Section 2 ──►│    FIM ≤ 0.05
    Section 3 ──►│    FIM ≤ 0.05
                 │
            ═════╪═════  Datum Axis A

Each section is checked independently.

What Circular Runout Controls

• On cylindrical surfaces: Circularity + concentricity to datum axis
• On flat surfaces (perpendicular to axis): Circular elements perpendicular to axis

2. Total Runout (↗↗)

FCF: ┌────┬──────┬────────┐
     │ ↗↗ │ 0.08 │ A      │
     └────┴──────┴────────┘

How It Works

The indicator sweeps across the entire surface while the part rotates continuously. The total variation must be within tolerance:

         Indicator moves along surface
    ╔═══════╦═══════╦═══════╦═══════╗
    ║       ║       ║       ║       ║
    ╚═══════╩═══════╩═══════╩═══════╝
                    │
              ══════╪══════  Datum Axis A

    Total FIM (entire surface) ≤ 0.08

What Total Runout Controls

• On cylindrical surfaces: Circularity + cylindricity + concentricity
• On flat surfaces: Flatness + perpendicularity to datum axis

Circular vs. Total Runout

A shaft might have:

• Circular runout of 0.05 (individual sections must be round)
• Total runout of 0.10 (accounts for taper and straightness)

Runout on Different Surfaces

Cylindrical Surfaces

Most common application—ensures shaft is concentric with datum axis:

    ┌────────────────────┐
    │   ┌────────────┐   │
    │   │            │   │ ← Controlled surface
    │   └────────────┘   │
    └────────────────────┘
            │
      Datum Axis A

Flat Surfaces (Perpendicular)

Controls wobble of end faces:

    ┌───────────┐
    │           │ ← End face
    ├───────────┤    (circular runout controls wobble)
    │           │
    └───────────┘
          │
    Datum Axis A

Tapered Surfaces

Total runout controls the entire taper:

        ╲         ╱
         ╲       ╱
          ╲     ╱
           ╲   ╱
            ╲ ╱
             │
       Datum Axis A

Common Applications

Runout vs. Other Controls

Key Takeaways

• Runout controls require rotation about a datum axis
• Circular runout: checks individual cross-sections independently
• Total runout: checks entire surface simultaneously (more restrictive)
• Total runout controls form elements that circular runout does not
• Always requires a datum axis reference
• Inspected using dial indicator while rotating part

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