Hand Tools, Power Tools and Manual Machining Operations
Hand tools and manual machining underpin everything else in the trade. The exam tests tool selection, cutting geometry, tapping and reaming practice, safe use of portable power tools, and the hand-fitting skills used to bring a part to a fine tolerance.
Files and hand cutting
A single-cut file produces a smoother finish; a double-cut file removes material faster. Grades run from rough to dead-smooth, and length matters - a file should be long enough to stroke the full work surface. Always fit a handle; a bare tang in the palm causes serious injury. Chalk on a file reduces pinning when filing aluminium. Draw filing, with the file held at 90° to the work and moved along the axis, produces a flat, fine finish.
Hacksaws and chisels
Select pitch so at least two or three teeth contact the section being cut: 14 TPI for thick sections, 24 or 32 TPI for thin wall tube, or the blade snags and strips teeth. Apply pressure on the forward stroke only.
Tapping, reaming and hand fitting
For metric threads the tap drill is approximately major diameter minus pitch: M10 × 1.5 uses an 8.5 mm drill. For inch threads it is major diameter minus 1/TPI: 1/4-20 uses 0.250 − 0.050 = 0.200 in (a #7 drill, 0.201 in). These give about 75% thread, the standard trade compromise. Use the correct lubricant - cutting fluid on steel, kerosene on aluminium. Reamers remove 0.1–0.3 mm after drilling and must be turned in the cutting direction only; reversing dulls the edges.
Portable power tools
Die grinders and angle grinders use rated wheels, guards, and eye and face protection. Hold work in a vise, never against your hand. Check the wheel for cracks, run the tool at no load briefly, and never exceed the wheel's marked maximum speed.
Worked example
A 1/2-13 threaded hole must be tapped in mild steel. Tap drill = 0.500 − 1/13 = 0.500 − 0.0769 = 0.4231 in, so a 27/64 in (0.4219 in) drill is used. Reasoning: the 1/TPI rule produces roughly 75% thread; a 29/64 in (0.4531 in) drill would give a shallow, weak thread, while too small a hole risks tap breakage.
Traps
Using a bent tap or excessive force instead of backing off to break chips; reversing a hand reamer; choosing a coarse blade for thin tube; and using a file without a handle or a grinder without its guard.