Machining Processes and Machine Tools
What this domain tests
Machining Processes and Machine Tools examines the basic machines in a maintenance workshop - centre lathe, drilling machine, milling machine, shaping machine, grinder - and the parameters that control them: cutting speed, feed, depth of cut, tool geometry and coolant. CNC basics, work holding and operation selection may also appear.
Core rules
- Cutting speed depends on tool and work material: HSS in mild steel roughly 20–30 m/min; carbide can run several times faster. Spindle speed N = 1000v/(πD).
- Feed is the distance moved per revolution (lathe, mm/rev) or per tooth (milling, mm/tooth). Depth of cut is the radial engagement, not the feed.
- Turning time T = L/(f × N), where L includes approach and overtravel. Milling feed rate = fz × z × N, with z = number of teeth.
- Tool geometry matters: positive rake for ductile work, zero or negative rake for interrupted cuts and hard materials; use coolant to control heat and chip clearance.
- On a drilling machine, the drill axis must align with the hole; use a pilot hole for large diameters.
Worked example
A 150 mm long shaft is turned at 400 rev/min with a feed of 0.25 mm/rev. Ignoring approach, time = 150/(0.25 × 400) = 1.5 min. For a milling cut with a 4-tooth cutter at 500 rev/min and feed 0.05 mm/tooth, table feed = 0.05 × 4 × 500 = 100 mm/min. A 300 mm cut then takes 3 min.
Traps
Mixing feed per revolution with feed per minute; using diameter as radius in speed calculations; forgetting approach length; taking too heavy a depth of cut on a small lathe; running a carbide tool without rigidity or coolant where required.