Dial indicator shaft alignment procedure

Shaft alignment using a dial indicator is a common method for ensuring that two coupled shafts (such as those in a motor and pump) are properly aligned to avoid vibration, excessive wear, and potential equipment failure. Misalignment can cause premature bearing and seal failure, increased energy consumption, and other mechanical issues.

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Here’s a step-by-step guide to using a dial indicator for shaft alignment:

Shaft Alignment Procedure Using a Dial Indicator:

1. Preliminary Steps:

- Safety First: Make sure both machines (e.g., motor and pump) are de-energized and locked out according to safety procedures before beginning the alignment process.

- Visual Inspection: Inspect the machinery for any obvious signs of wear or damage, like bent shafts or damaged couplings, and fix them before proceeding with the alignment.

- Initial Positioning: Roughly align the shafts by visual inspection and ensure that both the motor and driven equipment are level and securely mounted.

2. Mounting the Dial Indicator:

- Setup the Dial Indicator:

- Attach the dial indicator to a magnetic or clamp-style base.

- Position the dial indicator so that its tip contacts the shaft or coupling of the stationary machine (this will be your reference point).

Typically, two dial indicators are used in the reverse dial method, but a single dial can also be used with careful rotation. The dial indicators will measure both the angular misalignment and the parallel (offset) misalignment.

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- Dial Indicator Placement:

- Indicator A: Mount on the shaft of the stationary machine, with the plunger tip on the shaft or coupling of the movable machine.

- Indicator B: Mount on the shaft of the movable machine, with the plunger tip on the shaft or coupling of the stationary machine.

- Position: Both indicators should be 180° apart (usually horizontally).

3. Rotate the Shafts:

- Rotate Together: Slowly rotate both the motor and the driven equipment shafts together, ensuring the dial indicators stay in contact with the surface.

- Take Readings: Stop at four positions around the coupling and take readings at 0°, 90°, 180°, and 270°.

Ensure that the shafts are rotated simultaneously to avoid errors caused by coupling movement. The readings will show the amount of misalignment between the two shafts in both the horizontal and vertical planes.

4. Analyzing the Readings:

- Vertical Misalignment (0° and 180° readings):

- Compare the readings from the dial indicators at the top (0°) and bottom (180°) positions.

- A difference between these two readings indicates vertical misalignment.

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- Horizontal Misalignment (90° and 270° readings):

- Compare the readings at the 90° (right side) and 270° (left side) positions.

- A difference here indicates horizontal misalignment.

5. Adjusting the Alignment:

- Vertical Adjustments:

- If the vertical misalignment is detected (difference in the 0° and 180° readings), use shims to raise or lower the motor or driven equipment until the vertical misalignment is corrected.

- Remove or add shims beneath the feet of the machine, ensuring that all four feet remain level and secure.

- Horizontal Adjustments:

- If the horizontal misalignment is detected (difference in the 90° and 270° readings), loosen the mounting bolts on the motor and use a soft mallet or pry bar to carefully shift the motor left or right.

- Re-tighten the bolts and take new readings to confirm the correction.

6. Recheck the Alignment:

After making adjustments:

- Rotate the shafts again to check if the readings at all positions (0°, 90°, 180°, 270°) are within the acceptable tolerance specified by the machine manufacturer (usually within 0.05 mm or 0.002 inches)

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- Shim or shift further if necessary based on the re-readings.

7. Tighten Bolts and Final Checks:

- Once the alignment is within tolerance, tighten all bolts on the motor and driven equipment securely. Ensure the machine stays in alignment as you tighten (you may need to recheck readings after tightening to ensure nothing shifted).

- Run the Machine: After the alignment is completed and all bolts are tightened, run the machine at normal operating conditions and check for any abnormal vibrations or noise.

Types of Misalignment Detected by Dial Indicator:

1. Offset Misalignment: Occurs when the centerlines of the shafts are parallel but not collinear. This can be detected by a constant reading difference across the 0° and 180° (vertical plane) or 90° and 270° (horizontal plane) positions.

2. Angular Misalignment: Occurs when the shafts meet at an angle, typically detected by differing readings across all positions (0°, 90°, 180°, and 270°). The readings will vary in a pattern indicating that one end of the shafts is tilted relative to the other.

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Key Tips for Accurate Alignment:

- Ensure Repeatability: If readings vary greatly when rechecking the same position, ensure the dial indicator is securely mounted and there’s no play in the shafts or couplings.

- Clean Shaft Surfaces: Dirt or burrs on the shaft surface can cause inaccurate readings. Clean all surfaces thoroughly before starting.

- Use Consistent Force: When rotating the shafts, do it slowly and smoothly to avoid errors.

- Check for Soft Foot: Before alignment, check if there’s a “soft foot” condition (i.e., one foot of the machine isn’t firmly touching the base) and correct it by shimming as necessary.

By following these steps, you’ll achieve proper shaft alignment, reducing equipment stress, improving operational efficiency, and minimizing the risk of premature failure.