Shaft Alignment & Machinery Installation Flashcards

What is 'bracket sag' and how does it affect dial indicator alignment readings?

Answer: The downward deflection of the dial indicator bracket due to gravity, which introduces a false reading that must be measured and subtracted

Bracket sag is the gravitational deflection of the dial indicator arm when it extends outward; this sag adds an error to bottom readings and must be measured independently and subtracted from alignment calculations.

In laser shaft alignment, what does the detector (PSD) measure?

Answer: The position of the laser beam striking its surface, which is used to calculate shaft offset and angle

The position-sensitive detector (PSD) measures the exact X-Y coordinates where the laser beam strikes its surface; changes in beam position as the shafts are rotated are used to calculate misalignment values.

What type of misalignment is indicated when vibration phase measurements show a 180° phase difference across the coupling in the radial direction?

Answer: Parallel (offset) misalignment

A 180° radial phase difference across the coupling is a classic indicator of parallel misalignment, as the two shaft centerlines are offset and move in opposition to each other.

Which coupling type provides the greatest tolerance for angular misalignment while transmitting torque?

Answer: Gear coupling

Gear couplings use meshing gear teeth that can accommodate significant angular misalignment (typically up to 1.5° per gear mesh) while transmitting high torque loads.

What is 'cold alignment target' or 'alignment offset' in precision machinery installation?

Answer: An intentional misalignment introduced during cold installation to compensate for predicted thermal growth at operating temperature

A cold alignment target (thermal offset) intentionally misaligns the machine when cold so that, after thermal expansion at operating temperature, the shafts reach the desired aligned position.

What is the recommended hold-down bolt tightening sequence to minimize soft foot when installing machinery?

Answer: Tighten diagonally opposite bolts in a star pattern, gradually increasing torque in multiple passes

Tightening diagonally opposite bolts in a cross/star pattern and incrementally increasing torque prevents the machine frame from warping and ensures even clamping force across all feet.

For a machine running at 3,600 RPM (60 Hz), what is the industry-standard acceptable residual misalignment for precision alignment?

Answer: ≤ 0.002 inch (0.05 mm) offset and ≤ 0.5 mrad angle

ISO 10816 and ANSI/ASA S2.75 precision alignment standards for high-speed machinery (3,600 RPM) require residual offset ≤ 0.002 inch and angular misalignment ≤ 0.5 mrad to avoid excessive coupling and bearing loads.