Trade Practical
Trade Practical tests job execution: reading the job drawing, choosing tools and workholding, sequencing operations, working safely, and inspecting the finished part. The exam expects a practical sequence, not just a final dimension.
Planning and execution rules
- Read the whole drawing first; mark datums, critical dimensions, fits, and surface finish.
- Select workholding and tooling before cutting; check tool sharpness and machine guards.
- Sequence operations so that finishing cuts are last and critical surfaces are protected.
- Inspect as you go; check before removing the job from the machine when possible.
- Safety: isolate the machine before tool changes, control chips, and use the correct PPE.
Worked example
Find the tapping drill size for an M12 × 1.75 internal thread. Tapping drill = major diameter − pitch = 12 − 1.75 = 10.25 mm. Select the nearest standard drill, 10.2 mm. Reason: the tap removes material equal to the thread depth on each side; a hole that is too small tears the thread or breaks the tap, while too large a hole leaves a shallow thread. Chamfer the hole, hold the tap square, and use cutting lubricant.
Traps
Using 12 mm as the drilling size; tapping without a chamfer; starting the tap out of square; forcing a blunt tap; skipping lubricant; measuring a precision surface with a vernier when the drawing calls for a micrometer.