Hand Tools, Bench Work and Fitting
What this domain tests
Hand Tools, Bench Work and Fitting covers the operations done at a fitting bench: marking out, sawing, filing, chiselling, drilling, tapping, reaming, scraping and assembly. The exam checks tool selection, safe technique, and the calculations behind tap-drill size, file grade and hacksaw blade pitch.
Core rules
- Marking: use a surface plate, scriber, centre punch and dividers; lay out from a datum, not from a rough edge. Centre-punch before drilling to stop the drill wandering.
- Files are graded by cut: rough (bastard), medium (second cut), smooth. Use a file card to clean pins; never file without a handle.
- Hacksaw: 18 teeth per inch for thick sections and soft metals, 24–32 TPI for thin tube and sheet; at least two teeth must be in contact.
- Tap drill size for a metric coarse thread: drill diameter = major diameter − pitch. For M10 × 1.5, use 8.5 mm. For a forming tap, the hole is slightly larger; follow the tap manufacturer's chart.
- Tapping: start square, use cutting fluid, and back off a quarter turn periodically to break chips.
Worked example
A bracket needs an M12 × 1.75 tapped hole in mild steel. Tap drill = 12 − 1.75 = 10.25 mm; the nearest standard drill is 10.2 mm, which gives about 75% thread engagement. Drill at 10.2 mm, countersink, then use taper, second and plug taps in sequence with tapping compound.
Traps
Using a wood saw or wrong TPI; tapping without a pilot hole; forcing a tap and breaking it; filing soft aluminium with a clogged file; clamping a finished surface directly in the vice jaws without soft jaws.