Tools, Measuring Instruments and Workshop Equipment
This domain examines tool selection, precision measurement, calibration and care of workshop equipment. The exam favours least count, zero error, torque procedure and safe use of presses and lifting gear.
Core rules
- Vernier caliper least count is usually 0.02 mm. Read the main scale, add the coinciding vernier division multiplied by the least count, then subtract a positive zero error or add a negative one.
- Micrometer least count is usually 0.01 mm. Clean the faces, use the ratchet stop and check zero before measuring. Do not clamp hot, rough or rotating parts.
- Dial gauge and bore gauge: keep the plunger perpendicular to the surface. Use a bore gauge to check cylinder taper and out-of-round, not just diameter.
- Torque wrench: use a click type only for tightening, never as a breaker bar. Store at the lowest setting and recalibrate periodically. Tighten cylinder heads from the centre outward in the specified sequence.
- Feeler gauge for valve clearance and gap checks; compression tester with the throttle open and all plugs removed; hydraulic press with a cage or guard.
Worked example
A vernier reads 24 mm on the main scale and the 13th vernier line coincides; least count is 0.02 mm. Reading = 24 + (13 × 0.02) = 24.26 mm. If the closed-jaw zero error is +0.02 mm, true size = 24.26 − 0.02 = 24.24 mm.
Traps
- Parallax error from viewing the scale at an angle.
- Using a torque wrench to loosen a seized bolt.
- Measuring a hot engine part and comparing it with a cold clearance specification.
- Forgetting zero error or using a damaged micrometer face.