Millwright Certification Precision Shaft Alignment Techniques 2

Question 1

What is soft foot, and why must it be corrected before performing shaft alignment?

Accepted Answer

It occurs when one or more machine feet do not sit flat on the base, causing the frame to distort when bolts are tightened

Answer

Soft foot occurs when a machine foot does not make full contact with the baseplate, causing the machine frame to flex when the hold-down bolt is tightened, which distorts bearing bores and creates unpredictable alignment changes.

Question 2

In reverse dial indicator alignment, what does each indicator measure?

Accepted Answer

Each indicator measures the radial position of the opposite shaft, giving both offset and angularity data

Answer

In reverse indicator alignment, two dial indicators are mounted on opposite shafts pointing at each other. Each reads the runout of the opposite shaft, and the combined data from both reveals both offset and angular misalignment.

Question 3

What is thermal growth, and how is it accounted for during cold alignment?

Accepted Answer

Predictable increase in machine height as components reach operating temperature, compensated by offsetting cold alignment targets

Answer

Thermal growth is the vertical and horizontal expansion of machine casings and bearing pedestals as they heat to operating temperature. Cold alignment targets are deliberately offset to ensure correct alignment at running temperature.

Question 4

Why is it important to use proper shim practices during alignment?

Accepted Answer

Incorrect shimming introduces errors: corroded shims, too many shims, or wrong thickness shims prevent accurate and stable alignment

Answer

Poor shimming practices (using too many shim layers, corroded shims, bent shims, or inadequate shim area) create soft foot conditions, compress over time, and prevent the machine from maintaining its aligned position.

Question 5

What alignment readings at the 12, 3, 6, and 9 o'clock positions indicate pure parallel (offset) misalignment with no angularity?

Accepted Answer

The 12 and 6 readings are equal and opposite, and the 3 and 9 readings are equal and opposite

Answer

Pure parallel offset produces equal and opposite readings at the 12/6 and 3/9 positions because the indicator traces a circle that is offset from center but not tilted, creating symmetric deflections.

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Millwright Certification Precision Shaft Alignment Techniques 2