433A Alignment and Levelling 3 — Questions and Answers
Question 1: What is the minimum number of dial indicator readings required for the reverse indicator alignment method?
- 2 readings per indicator
- 4 readings per indicator (12, 3, 6, and 9 o'clock) (Correct answer)
- 6 readings per indicator
- 8 readings per indicator
Correct answer: 4 readings per indicator (12, 3, 6, and 9 o'clock)
The reverse indicator method requires a minimum of four readings per indicator taken at the 12, 3, 6, and 9 o'clock positions. These four points mathematically define both the offset and angular misalignment in each plane.
Question 2: What is the effect of an incorrect bolt-bound condition during alignment?
- The bolts become too tight
- The machine cannot be moved horizontally because the bolt contacts the side of the hole (Correct answer)
- The base cracks under the bolt
- The coupling fails
Correct answer: The machine cannot be moved horizontally because the bolt contacts the side of the hole
A bolt-bound condition occurs when the hold-down bolt contacts the edge of the mounting hole, preventing further horizontal movement in the needed direction. The millwright must offset the bolt holes or use oversized holes to resolve this.
Question 3: When using an optical alignment instrument (jig transit), what does the crosshair target represent?
- The center of gravity of the machine
- A fixed reference point representing the true centerline of the bore or surface being aligned (Correct answer)
- The thermal expansion point
- The coupling center
Correct answer: A fixed reference point representing the true centerline of the bore or surface being aligned
The crosshair target is positioned at the center of a bore or on a reference surface to represent the true centerline. The jig transit telescope then sights on multiple targets to verify that all reference points are in proper alignment.
Question 4: What type of soft foot is caused by a bent or warped machine foot?
- Parallel soft foot
- Angular soft foot (Correct answer)
- Induced soft foot
- Reactive soft foot
Correct answer: Angular soft foot
Angular soft foot occurs when a machine foot is bent, warped, or the baseplate surface is not flat, causing the foot to rock like a chair with one short leg. It requires tapered or stepped shims to correct.
Question 5: Why should alignment be rechecked after the final bolt torque?
- To verify the laser equipment is accurate
- Because torquing bolts can shift the machine position or reveal soft foot conditions (Correct answer)
- To satisfy documentation requirements only
- To confirm the coupling gap has not changed
Correct answer: Because torquing bolts can shift the machine position or reveal soft foot conditions
Final bolt torquing can cause small but significant shifts in machine position due to uneven clamping forces, soft foot effects, or dowel pins engaging. A final alignment check confirms the machine is still within tolerance.
Question 6: What is the purpose of pre-alignment checks before beginning precision shaft alignment?
- To determine the type of coupling installed
- To identify and correct foundation, baseplate, and mechanical issues that would prevent achieving or holding alignment (Correct answer)
- To select the correct laser alignment tool
- To measure the motor voltage
Correct answer: To identify and correct foundation, baseplate, and mechanical issues that would prevent achieving or holding alignment
Pre-alignment checks include inspecting the foundation, verifying baseplate flatness, checking for soft foot, inspecting coupling condition, checking for pipe strain, and verifying bolt hole condition — all issues that must be resolved before precision alignment can succeed.
433A Alignment and Levelling 3
What is the minimum number of dial indicator readings required for the reverse indicator alignment method?