Bench Work
Core Concepts
Bench work covers hand operations: marking out, sawing, filing, chipping, scraping, drilling by hand, tapping and dies, and reaming. You must know the tools and their correct use: scribers, dividers, calipers, surface plate, V-block, angle plate, try square, centre punch, prick punch, hammers, chisels, files (flat, half-round, round, triangular, square), hacksaw blades (tooth pitch selection), taps and dies, and reamers.
Key Skills and Traps
Understand marking-out datum selection and why a datum must be flat and true. Know file classifications (single-cut vs double-cut, bastard, second-cut, smooth) and the correct technique - pressure on the forward stroke only. Saw blade pitch: coarse teeth for soft, thick sections; fine teeth for thin tube or sheet. Tapping requires the correct drill size: for metric coarse threads, tap drill diameter ≈ major diameter − pitch. Traps include confusing tap vs die (tap cuts internal, die external), using the wrong drill size, or forgetting to use cutting fluid and back off the tap to break chips.
Worked Example / Rule of Thumb
For an M10 × 1.5 thread, tap drill = 10 − 1.5 = 8.5 mm. For an M8 × 1.25, drill = 8 − 1.25 = 6.75 mm (use 6.8 mm). Always check the thread standard; for inch threads use the tables. When filing, use a file card to clean the file; never tap it on the bench.