Machine Tools and Machining Operations
What the domain tests
Machine Tools and Machining Operations tests lathe, drilling, milling, grinding and shaping operations. You must calculate speeds and feeds, select cutters and workholding, and apply safety rules.
Core rules
- Cutting speed is the surface speed of the work or cutter, usually in m/min. Spindle speed N = 1000 × CS / (π × D), where D is diameter in mm.
- Feed is the distance moved per revolution or per tooth. Depth of cut is the thickness removed in one pass. Roughing removes material quickly; finishing gives accuracy and surface finish.
- Use the correct workholding: three-jaw chuck for round work, four-jaw for irregular work, machine vice for milling, clamps for large plates. Support long work.
- Keep guards in place, never leave a chuck key, stop the machine before measuring, and never reach across a rotating workpiece.
- Select HSS or carbide tooling for the material; use coolant where appropriate.
Worked example
A 20 mm diameter mild steel bar is to be turned with a high-speed steel tool at a cutting speed of 25 m/min. N = 1000 × 25 / (3.142 × 20) = 25,000 / 62.84 ≈ 398 rpm. Set about 400 rpm, take a modest roughing depth, then a finishing pass. If the diameter were 40 mm, the speed would halve to about 200 rpm for the same cutting speed.
Traps
Using radius instead of diameter doubles the speed. Too high a speed burns tools; too low a speed gives poor finish. Do not measure while the lathe rotates, leave the key in the chuck, or machine without guarding.