Mechanical assembly, alignment, and preventive maintenance
This domain tests correct assembly practice, alignment measurement, fastening, lubrication, and planned maintenance. Expect bearing fits, coupling alignment, belt tension, torque sequence, and PM records.
Core rules
- Clean and inspect mating surfaces before assembly; remove burrs and contamination. Check bearing fits against the specified shaft and housing tolerances.
- Tighten threaded fasteners in a crossing pattern and in stages to the specified torque. Use the specified lubricant because it changes friction and preload.
- Check soft foot before shimming a motor or pump; a soft foot distorts the frame and makes alignment readings unstable.
- Coupling alignment uses dial indicators or laser systems; correct angular and parallel misalignment within the manufacturer's tolerance.
- Preventive maintenance follows intervals and condition data: lubrication, belt tension, fastener torque, vibration, temperature, and filter changes.
Worked example
A bolt is specified at 40 N·m. A torque wrench with a 0.30 m handle requires a force of F = T/L = 40/0.30 = 133 N at the handle. If the wrench is used with an extension that changes effective length, the indicated torque must be corrected according to the wrench maker's formula. The reasoning: torque is force times perpendicular distance, and the setting is only valid for the tool's calibrated length.
Traps
Using an impact wrench to final-torque a fastener; oiling threads when the specification is dry; over-greasing a bearing; ignoring soft foot; and aligning a coupling before checking runout. These cause vibration, premature bearing failure, and lost marks.