AIT Technical Skills & Application 5 — Questions and Answers
Question 1: An apprentice millwright is installing a v-belt drive system. Belt tension should be checked by measuring deflection at the midpoint of the longest span. What is the correct procedure?
- Apply force equal to 10% of motor horsepower and measure deflection in millimeters
- Apply a specified force perpendicular to the belt span and measure deflection — typically 1/64 inch per inch of span (Correct answer)
- Tension until the belt hums at the motor's operating frequency
- Tighten until slippage is eliminated under full load, then add 10%
Correct answer: Apply a specified force perpendicular to the belt span and measure deflection — typically 1/64 inch per inch of span
The standard method is to apply a known perpendicular force at the belt midpoint and measure deflection; the target is approximately 1/64 inch of deflection per inch of free span.
Question 2: In electrical motor theory, what is 'slip' in an induction motor?
- The difference in voltage between phases under unbalanced load
- The percentage difference between synchronous speed and actual rotor speed (Correct answer)
- Belt slippage on the motor sheave
- The amount of current drawn above full-load amperage during starting
Correct answer: The percentage difference between synchronous speed and actual rotor speed
Slip is the difference between the rotating magnetic field's synchronous speed and the rotor's actual speed, expressed as a percentage; slip is necessary for torque production in induction motors.
Question 3: A welder is using the GTAW (TIG) process on stainless steel. Which shielding gas selection is correct?
- 100% CO2
- 75% Argon / 25% CO2 (C25)
- 100% Argon (Correct answer)
- 100% Helium mixed with 5% hydrogen
Correct answer: 100% Argon
Pure argon is the standard shielding gas for GTAW on stainless steel; CO2-containing mixes are used for GMAW and cause oxidation that is incompatible with the TIG process.
Question 4: When using an angle grinder with a cutting disc, which PPE item is most critical beyond standard safety glasses?
- Leather gloves rated for heat
- A full face shield rated for grinding operations (Correct answer)
- Steel-toed boots
- A hard hat with class E rating
Correct answer: A full face shield rated for grinding operations
Cutting discs can shatter and eject fragments at high velocity; a full face shield protects the entire face from debris that safety glasses alone cannot cover.
Question 5: A pipefitter is making a branch connection using a weldolet fitting. What is the primary advantage of a weldolet over a standard tee fitting for this application?
- It requires no welding and can be installed while the line is in service
- It allows a branch connection of any size without cutting and replacing the run pipe with a full tee (Correct answer)
- It provides a threaded connection that is leak-free at high pressure
- It reduces flow turbulence more effectively than any other fitting type
Correct answer: It allows a branch connection of any size without cutting and replacing the run pipe with a full tee
A weldolet is an integrally reinforced branch fitting that welds directly onto the run pipe with only a hole cut, eliminating the need to cut out a full pipe section and insert a tee.
Question 6: In precision metalwork, surface finish is measured in microinches (µin) Ra. A drawing calls for a surface finish of 32 µin Ra. Which process would typically produce this finish directly?
- Rough turning on a lathe (63–125 µin Ra)
- Finish turning or milling (16–63 µin Ra)
- Precision grinding (8–32 µin Ra) (Correct answer)
- Lapping or honing (1–8 µin Ra)
Correct answer: Precision grinding (8–32 µin Ra)
Precision cylindrical or surface grinding routinely achieves 8–32 µin Ra, placing 32 µin Ra at the coarser end of the grinding range, making it the correct matching process.
Question 7: An HVAC technician is commissioning a newly installed split-system air conditioner. Before charging refrigerant, why must the system be evacuated to at least 500 microns?
- To verify the compressor oil level before startup
- To remove air and moisture that would contaminate the refrigerant, raise condensing pressure, and cause acid formation (Correct answer)
- To pre-charge the system with nitrogen as a holding charge
- To test the electrical connections by running the compressor under vacuum
Correct answer: To remove air and moisture that would contaminate the refrigerant, raise condensing pressure, and cause acid formation
Air and moisture are non-condensables that raise system pressures and reduce efficiency; moisture reacts with refrigerant and oil to form acids that destroy compressor components.
AIT Technical Skills & Application 5
An apprentice millwright is installing a v-belt drive system.
Belt tension should be checked by measuring deflection at the midpoint of the longest span.
What is the correct procedure?