Permissible Shaft Radial Runout Calculator | Vibromera.eu • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors Permissible Shaft Radial Runout Calculator | Vibromera.eu • Portable balancer, vibration analyzer "Balanset" for dynamic balancing crushers, fans, mulchers, augers on combines, shafts, centrifuges, turbines, and many others rotors
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Permissible Shaft Radial Runout Calculator

Calculate maximum allowable shaft runout relative to bearings

Calculation Parameters

Based on API 686 and machinery alignment standards






RPM





Calculation Results

Maximum Permissible Runout (TIR):
API 686 Limit:
Speed Factor:
Location Factor:

Runout Severity Assessment:

Excellent: Less than 25% of calculated limit
Good: 25-50% of calculated limit
Acceptable: 50-75% of calculated limit
Marginal: 75-100% of calculated limit – consider correction

How the Calculator Works

Shaft Runout Definition

Shaft runout is the total indicated reading (TIR) of radial displacement measured while rotating the shaft slowly (typically by hand). It indicates shaft straightness and mounting accuracy.

API 686 Standard

API 686 provides guidelines for permissible shaft runout:

TIR ≤ 50 μm (0.002 inches) or D/2000

whichever is greater, where D is the shaft diameter in mm.

Speed-Based Limits

For high-speed machinery, more stringent limits apply:

  • < 1800 RPM: Standard limits
  • 1800-3600 RPM: 75% of standard
  • 3600-7200 RPM: 50% of standard
  • > 7200 RPM: 25% of standard

Location Factors

Runout limits vary by measurement location:

  • At coupling: Most critical – use base limit
  • Near bearing: 1.5× base limit
  • At midspan: 2× base limit
  • At overhang: 0.5× base limit (more stringent)

Causes of Excessive Runout

  • Bent shaft from improper handling or storage
  • Uneven bearing fit or misaligned bearing seats
  • Rotor imbalance causing permanent deformation
  • Thermal distortion from uneven heating
  • Manufacturing tolerances and machining errors

Measurement Best Practices

  • Use dial indicators with resolution of 0.001 mm (0.00005″)
  • Support shaft in V-blocks or on centers
  • Rotate slowly by hand, not under power
  • Take readings at multiple axial locations
  • Check for indicator sag on horizontal shafts
  • Clean shaft surface before measurement

Correction Methods

  • Minor runout: Precision balancing may help
  • Moderate runout: Shaft straightening (cold or hot)
  • Severe runout: Machining or shaft replacement
  • Bearing-related: Check and correct bearing fits

Usage Examples & Value Selection Guide

Example 1: Pump Shaft at Coupling

Scenario: Centrifugal pump shaft check before installation

  • Shaft Diameter: 60 mm
  • Speed: 2950 RPM
  • Machine Type: General machinery
  • Bearing Type: Ball bearings
  • Location: At coupling hub
  • Surface Finish: Good
  • Result: Max TIR = 38 μm (0.038 mm)
  • Typical reading: 15-25 μm acceptable
Example 2: Precision Spindle

Scenario: Machine tool spindle for CNC machining

  • Shaft Diameter: 80 mm
  • Speed: 8000 RPM
  • Machine Type: Precision equipment
  • Bearing Type: Ball bearings
  • Location: Near bearing
  • Surface Finish: Excellent
  • Result: Max TIR = 10 μm (0.010 mm)
  • Critical: Must be < 5 μm for precision work
Example 3: Large Compressor Rotor

Scenario: Centrifugal compressor shaft inspection

  • Shaft Diameter: 200 mm
  • Speed: 5400 RPM
  • Machine Type: Process machinery
  • Bearing Type: Sleeve bearings
  • Location: At midspan
  • Surface Finish: Good
  • Result: Max TIR = 50 μm (0.050 mm)
  • Note: Midspan allows 2× coupling limit

How to Choose Values

Machine Type Selection
  • Precision Equipment:
    • Machine tool spindles
    • Grinding machines
    • Optical equipment
    • Measurement instruments
  • General Machinery:
    • Electric motors
    • Standard pumps
    • Fans and blowers
    • Most industrial equipment
  • Process Machinery:
    • Compressors
    • Turbines
    • High-speed pumps
    • Critical process equipment
  • Heavy Machinery:
    • Rolling mills
    • Crushers
    • Large gearboxes
    • Mining equipment
Measurement Location Impact
  • At Coupling Hub:
    • Most critical location
    • Directly affects alignment
    • Use strictest limits
    • Check both faces and rim
  • Near Bearing:
    • Affects bearing life
    • 1.5× coupling limit OK
    • Check within 1 diameter of bearing
  • At Midspan:
    • Natural sag point
    • 2× coupling limit acceptable
    • Check for bent shaft
  • At Overhang:
    • Amplifies vibration
    • Use 0.5× normal limit
    • Critical for impellers
Surface Finish Effects
  • Excellent (Ra < 0.8 μm):
    • Ground or polished
    • No measurement error
    • Use for precision work
  • Good (Ra 0.8-1.6 μm):
    • Fine turned
    • Standard for most shafts
    • Minimal measurement error
  • Average (Ra 1.6-3.2 μm):
    • Normal turning
    • May affect readings
    • Clean before measuring
  • Rough (Ra > 3.2 μm):
    • Rough turned or milled
    • Significant measurement error
    • Consider machining
Speed Considerations
  • < 1800 RPM: Standard runout limits apply
  • 1800-3600 RPM: Reduce limits by 25%
  • 3600-7200 RPM: Reduce limits by 50%
  • > 7200 RPM: Reduce limits by 75%
  • Rule: Higher speed = tighter tolerance
Practical Measurement Tips
  • Setup: Use stable V-blocks or centers
  • Indicator: 0.001 mm resolution minimum
  • Rotation: Turn slowly by hand, mark high spot
  • Multiple readings: Check several axial positions
  • Temperature: Measure at room temperature
  • Documentation: Record readings on shaft sketch

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📘 Shaft Runout Calculator (API 686)

Determines permissible radial runout (TIR) per API 686 standard. Critical for high-speed equipment and precision mechanisms.
Rule: TIR ≤ max(50 μm; D/2000) where D is shaft diameter in mm.

💼 Applications

  • New Shaft Acceptance: Ø80 mm shaft. Measured: 35 μm. Limit: max(50; 40) = 50 μm. Passes ✓
  • Post-Repair Control: Shaft straightened after bending. Runout was 180 μm, after straightening: 45 μm. Ready for installation.
  • Vibration Diagnosis: 1× vibration growing. Checked runout: 95 μm. Limit for Ø100: 50 μm. Cause: Bent shaft or worn bearings.

Measurement Methods:

TIR (Total Indicator Reading): Full dial indicator reading. Peak-to-peak runout (2× amplitude).

Measurement: Mount shaft in V-blocks or lathe. Place dial indicator on bearing journal. Rotate slowly, note min and max readings.

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