Tools
Hand and power tools; precision measuring with the micrometer, vernier caliper and dial gauge; go/no-go gauging, torque wrenches and instrument care.
Tools, summary notes
- Covers hand tools, power tools and precision measuring equipment, together with their correct use, care and calibration.
- The micrometer measures to 0.01 mm: the sleeve gives whole and half millimetres, the thimble the hundredths. It has a ratchet or friction thimble so the measuring pressure is consistent, over-tightening distorts the frame and the reading.
- The vernier caliper measures external, internal and depth dimensions; the vernier scale resolves the fraction of a main-scale division, typically to 0.02 mm.
- The dial test indicator measures run-out, end-float and backlash by comparison rather than absolute size, and must be rigidly mounted to be meaningful.
- Go/no-go gauges give a rapid pass/fail against limits without reading a value, the GO end must enter, the NO-GO end must not.
- Torque wrenches must be set to the specified value, pulled smoothly at the handle centre, and returned to their lowest setting for storage so the spring does not take a set.
- Precision instruments are stored clean, dry and separated, never loose in a toolbox, and are checked for zero error before use.
- ⚠ Exam trap: the micrometer's ratchet exists to standardise the measuring FORCE, not to speed it up; and a dial gauge reads a difference, not a dimension.
- Micrometer resolution
- typically 0.01 mm, sleeve (mm and ½ mm) + thimble (0.01 mm)
- Vernier resolution
- typically 0.02 mm
- Go / no-go
- GO must enter · NO-GO must not
A micrometer reads 7.5 mm on the sleeve with the thimble showing 23. What is the measurement?
7.5 mm from the sleeve plus 0.23 mm from the thimble gives 7.73 mm. The half-millimetre mark on the sleeve is the commonest thing to overlook.
Why is a torque wrench wound back to its lowest setting before being put away?
A click-type wrench holds its setting with a spring under compression. Leaving it wound up lets the spring take a permanent set, so the wrench gradually reads high and applies less torque than indicated.
Tools concept map
Tools
Tools quiz
Tools, quiz
1. The micrometer shown has its sleeve reading 7.5 mm with the thimble on 22. The measurement is:
7.72 mm7.22 mm29.5 mm2. On the vernier shown the main scale has passed 13 mm and the fourth vernier division coincides with a main scale line. The reading is:
13.4 mm13.04 mm17 mm3. Which measuring tool reads to the highest precision?
MicrometerSteel ruleTape measure4. The ratchet on a micrometer thimble exists to:
Apply a consistent measuring forceSpeed up the measurementLock the reading5. A micrometer sleeve reads 7.5 mm and the thimble 23. The measurement is:
7.73 mm7.23 mm8.23 mm6. A dial test indicator is used to measure:
Run-out, end-float and backlash by comparisonAbsolute diameterSurface hardness7. With a go/no-go gauge, an acceptable part is one where:
The GO end enters and the NO-GO end does notBoth ends enterNeither end enters8. A click-type torque wrench is stored:
Wound back to its lowest settingAt its last used settingAt maximum setting9. Torque should be applied:
Smoothly, with the hand at the centre of the handleIn sharp jerksWith an extension bar for extra reach10. Before use, a precision instrument is checked for:
Zero error and damageWeightManufacturer