Portable Power Tools and Measuring Instruments
Portable Power Tools and Measuring Instruments
The exam tests safe use of drills, angle grinders, jigsaws, circular saws and sanders, plus correct reading of vernier calipers, micrometers, steel rules, squares and feeler gauges.
Core rules
- Power tools: check voltage and insulation, use an RCD, keep guards fitted, unplug before changing blades or discs, and clamp the work. A cutting disc must not be used for grinding, and a grinding disc must not be used for cutting.
- Angle grinder sparks are a fire risk; screen the work and keep flammables away. Wear eye protection, hearing protection and dust protection as required.
- Vernier caliper: read the main scale, then find the vernier line that coincides. A 0.02 mm vernier gives 0.02 mm per division.
- Micrometer: read the barrel in 0.5 mm steps and the thimble in 0.01 mm steps. Use the ratchet to avoid over-tightening.
- Steel rules are for approximate work; calipers and micrometers are for precision. Check zero error before measuring.
Worked example
A micrometer barrel shows 7.5 mm and the thimble reads 22 divisions. Reading = 7.5 + (22 × 0.01) = 7.72 mm. If the zero error were +0.02 mm, the true size would be 7.72 − 0.02 = 7.70 mm. Reasoning: the thimble adds hundredths to the barrel reading, and zero error is subtracted.
Traps
Parallax when reading a vernier; over-tightening a micrometer; using a caliper as a hammer or clamp; fitting a cutting disc to a grinder without checking its speed rating; measuring a moving workpiece.