Bench Work: Cutting, Filing, Drilling, Tapping and Fitting
What the domain tests
Bench Work covers cutting, filing, drilling, tapping and fitting to a tolerance. It tests process order, tool selection, speeds and lubricants, and the arithmetic needed for tapping and fitting.
Core rules
- File flat by crossing strokes and checking with a straightedge or square. Use a safe-edge file where one edge must not cut.
- For drilling, centre-punch, drill a pilot hole where appropriate, clamp the work, and select speed from material and drill diameter. Use coolant or lubricant for steel.
- Tapping drill size is approximately major diameter minus pitch. Use the correct tap sequence: taper, second, plug; keep the tap square and reverse to break chips.
- Deburr holes and edges. Fit parts by controlled filing, not force. Check squareness, parallelism and clearance as you go.
- Keep the bench vice and machine table clean; swarf under a workpiece causes inaccurate seating.
Worked example
An M8 × 1.25 tapped hole is required in mild steel. Tapping drill = 8 − 1.25 = 6.75 mm; use the standard 6.8 mm drill. Drill and countersink the hole, then start the taper tap square with light pressure. Apply cutting fluid, turn forward about half a turn, reverse to break the chip, and continue through the hole with second and plug taps.
Traps
A hole drilled to 8 mm leaves no thread; too small a hole overloads the tap and causes breakage. Other losses come from filing without checking square, drilling without clamping, and using a plug tap first. Do not forget to deburr before fitting.