[Project 3]: What is run-out?

Question

BlackTom AI · Accepted Answer

Run-out describes the deviation of a rotating shaft’s actual centerline from its true axis of rotation.

1) Relevant knowledge points and concepts
- Run-out is a geometric error in rotating parts: radial run-out (eccentricity, shaft centerline offset) and axial run-out (wobble or tilt along the axis).
- Total indicated run-out (TIR) is the measurable variation of a point on the shaft as it is rotated and is used to quantify run-out.
- Causes: bent shafts, improper mounting, machining inaccuracies, bearing wear or misalignment.
- Consequences: vibration, uneven bearing/seal wear, noise, reduced life of components.

2) Complete reasoning process (step by step)
- A perfectly straight shaft has a centerline that coincides with its true rotational axis. If the shaft is bent or mounted off-center, that centerline shifts as the part rotates.
- To detect this, a dial indicator is placed against the shaft surface and the shaft is rotated 360°. The indicator needle moves as the distance from the true axis to the measured point changes.
- The observed variation of the indicator during one revolution is the run-out (TIR).

3) Calculation example with intermediate steps
- Suppose indicator readings during rotation vary between 0.002" and 0.006".
- TIR = maximum reading − minimum reading = 0.006" − 0.002" = 0.004".
- That 0.004" represents the run-out — the extent the centerline deviates from the true axis at that measured point.

4) Why the correct answer is correct
- The provided correct choice states that run-out is “a condition where the centerline of the shaft has deviated from its true axis of rotation.” That directly matches the engineering definition: run-out quantifies the axis deviation (eccentricity/wobble) of the rotating element.

5) Why the other options are incorrect
- “Engine operated past TBO” refers to time-between-overhaul, unrelated to geometric run-out.
- “Main journal dimensions deviated from round” describes out-of-roundness (oval condition), not axis deviation.
- “Clearance between bearings and crankshaft worn beyond limits” describes bearing wear/clearance, which can contribute to run-out but is not the definition of run-out itself.

6) Conclusion
The correct answer is: “A condition where the centerline of the shaft has deviated from its true axis of rotation,” which matches the authoritative answer provided.

[Project 3]: What is run-out?单项选择题

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