Machining Fundamentals and Workshop Safety
Core Concepts
A machinist must understand how cutting tools remove metal: cutting speed (surface speed, m/min), feed (mm/rev or mm/min), depth of cut, and the relationship between them. Know the difference between speed and feed - a common trap is treating them as synonyms. Understand chip formation, rake and clearance angles, and why cutting fluids reduce heat and improve finish. Know machine classifications: lathe, drilling machine, milling machine, shaping, grinding, and CNC basics.
Safety Fundamentals
Safety questions are frequent and deceptively simple. Learn the hierarchy: machine guarding, emergency stop, correct PPE (safety glasses, safety shoes, no loose clothing, no jewellery, hair tied back), and safe work practices such as never measuring a rotating workpiece, never leaving a chuck key in the chuck, and never removing swarf by hand - use a hook or brush. Know electrical safety, lockout/tagout, fire classes (A solid, B liquid, C gas, D metal), and the correct extinguisher for each. Understand housekeeping, safe lifting, and hand-signal or communication rules around machines.
Typical Traps
Questions often swap 'wear safety glasses' with 'wear goggles over spectacles', confuse the fire class for a metal fire (Class D), or present a plausible but unsafe shortcut. Read every option for the unsafe action.
Worked Example / Rule of Thumb
Cutting speed formula: V = πDN/1000, where V is m/min, D is diameter in mm, N is rpm. Rule of thumb: if V and D are known, N = 1000V/(πD). For mild steel with HSS tool, V ≈ 30 m/min; for a 50 mm diameter, N ≈ 1000×30/(3.14×50) ≈ 191 rpm. Always round down and check the machine's available speeds.