Sawing, Filing, Drilling and Basic Benchwork
What is examined
This domain assesses hand skills: sawing to a line, blade choice and tension, filing flat and square, draw filing, drilling without wander or breakage, and piercing. Marks are lost for ragged edges, broken blades, off-square faces and damaged work.
Core rules
- Saw frame: fit the blade with teeth pointing toward the handle so cutting occurs on the forward stroke; tension the blade firmly but not so tight that it snaps. Support the work on a bench pin and saw with light, even strokes.
- Blade selection: 8/0 is finest, 6 is coarsest. Use 4/0–2/0 for thin sheet and tight curves; use coarser blades for thick stock and straight cuts. A coarse blade on thin sheet tears the metal.
- Filing: secure the work so the file is used with two hands where possible. Cross filing removes metal quickly; draw filing produces a flatter surface. Use the full length of the file, keep it flat, and do not rock it. Clean the file with a file card.
- File shapes: flat, half-round, three-square, round, warding and barrette. Choose the shape that reaches the feature without damaging adjacent surfaces.
- Drilling: centre punch first, then drill with the work clamped and supported underneath. Small drills need high spindle speed and light pecking feed with lubricant; withdraw often to clear chips. Use a backing piece to prevent tear-out.
- Piercing: drill a starter hole, thread the saw blade, re-tension, and cut just outside the line; file to the line afterwards.
Worked example
Cut a 20 mm square opening in 1.0 mm brass. Mark the square, centre punch and drill a 1 mm starter hole inside a corner. Select a 3/0 blade, thread it through the hole, tension the frame and saw just outside the line with the work supported on the bench pin. Remove the waste, then file to the line with a flat file, checking squareness against the bench and measuring the opening with a caliper. The reasoning is: fine blade for thin sheet and corners, starter hole for internal access, waste allowance for filing, and measurement after filing rather than trusting the saw cut.
Traps
Fitting the blade with teeth the wrong way; over-tensioning and snapping blades; sawing on the backstroke; filing without a handle; rocking a file and creating a rounded surface; drilling without a centre punch so the drill wanders; no backing support causing burrs and tear-out; using too much pressure and breaking small drills; filing hardened steel with a files that is not designed for it.