AIT Technical Skills & Application 3 — Questions and Answers
Question 1: A machinist is turning a steel shaft on a lathe and notices chatter marks on the finished surface. Which corrective action is most likely to eliminate the chatter?
- Increase cutting speed and depth of cut simultaneously
- Reduce cutting speed, increase rigidity by shortening tool overhang, and check for loose gibs (Correct answer)
- Switch to a larger nose radius insert to spread the cut
- Apply more coolant and increase feed rate
Correct answer: Reduce cutting speed, increase rigidity by shortening tool overhang, and check for loose gibs
Chatter is caused by resonant vibration; reducing speed, minimizing tool overhang for rigidity, and tightening any loose machine components directly addresses the root cause.
Question 2: In an electrical panel, what is the purpose of an equipment grounding conductor (EGC)?
- To carry normal operating current back to the source
- To provide a low-impedance fault path so overcurrent devices will trip during a ground fault (Correct answer)
- To balance voltage between phases in a three-phase system
- To prevent static electricity buildup on metal conduit
Correct answer: To provide a low-impedance fault path so overcurrent devices will trip during a ground fault
The EGC creates a low-impedance return path for fault current, ensuring enough current flows to trip the breaker or fuse quickly and clear the fault.
Question 3: When cutting threads with a tap in a blind hole, what is the most important practice to prevent tap breakage?
- Use maximum torque to drive the tap through chips
- Back the tap out half a turn for every full turn forward to break chips (Correct answer)
- Cut threads without lubricant so chips eject freely
- Use a plug tap all the way to the bottom of the hole
Correct answer: Back the tap out half a turn for every full turn forward to break chips
Reversing the tap periodically breaks the chip and prevents chip packing, which is the primary cause of tap breakage in blind holes.
Question 4: A pipefitter is selecting pipe for a steam system operating at 150 psi and 365°F. Which material is the standard choice?
- PVC Schedule 80
- CPVC
- Carbon steel — ASTM A53 Grade B (Correct answer)
- Copper Type M
Correct answer: Carbon steel — ASTM A53 Grade B
Carbon steel A53 Grade B is the standard for steam piping above 212°F; plastic materials cannot withstand the temperature, and copper Type M is not rated for high-pressure steam.
Question 5: What does the term 'tolerance stack-up' mean in precision assembly work?
- A method of measuring multiple parts simultaneously with a single gauge
- The cumulative effect of individual part tolerances that can cause the final assembly dimension to be out of specification (Correct answer)
- Stacking shims to bring a shaft into alignment
- The process of sorting parts into tolerance bins before assembly
Correct answer: The cumulative effect of individual part tolerances that can cause the final assembly dimension to be out of specification
Tolerance stack-up occurs when individual part tolerances combine (add) across multiple components, potentially pushing the final assembled dimension beyond the acceptable range.
Question 6: In arc welding, what is the function of flux in a shielded metal arc welding (SMAW) electrode coating?
- To increase the amperage capacity of the electrode
- To provide shielding gas and form slag that protects the molten weld pool from atmospheric contamination (Correct answer)
- To preheat the base metal before the arc starts
- To add alloying elements only — shielding gas comes from the cylinder
Correct answer: To provide shielding gas and form slag that protects the molten weld pool from atmospheric contamination
The flux coating on SMAW electrodes decomposes under heat to produce shielding gas and forms a slag blanket that protects the weld pool from oxygen and nitrogen contamination.
Question 7: An industrial maintenance technician is performing a laser shaft alignment. The acceptable final angularity tolerance for a standard motor-pump coupling at 1800 RPM is typically within how many mils/inch?
- Less than 0.5 mils/inch
- Less than 1.0 mil/inch (Correct answer)
- Less than 2.0 mils/inch
- Less than 5.0 mils/inch
Correct answer: Less than 1.0 mil/inch
Industry standard for angularity on general machinery at 1800 RPM is typically ≤1.0 mil/inch (0.001 in/in), though tighter tolerances apply at higher speeds.
AIT Technical Skills & Application 3
A machinist is turning a steel shaft on a lathe and notices chatter marks on the finished surface.
Which corrective action is most likely to eliminate the chatter?