Machine Tools and Machining Processes
Machine Tools and Machining Processes
This domain covers the centre lathe, drilling machine, milling machine and grinding, including cutting speeds, feeds, workholding and safe operation.
Core rules
- Spindle speed: N = 1000 × Vc / (π × D), where Vc is cutting speed in m/min and D is diameter in mm. Keep units consistent.
- Turning operations include facing, parallel turning, taper turning, knurling, parting off and thread cutting. Set the tool on centre height and clamp the work securely.
- Drilling: use a centre drill first for accuracy, then the twist drill. Clear swarf with a brush, never by hand, and clamp thin sheet.
- Milling: up-milling opposes the feed and gives a better finish on some materials; down-milling needs backlash compensation. Climb milling is not simply a finishing choice.
- HSS tools suit mild steel and many plastics; carbide allows higher speeds but is brittle. Use coolant where appropriate.
Worked example
A 20 mm twist drill is to drill mild steel at Vc = 30 m/min. N = 1000 × 30 / (π × 20) = 477 rpm. With a feed of 0.15 mm/rev, feed rate = 477 × 0.15 ≈ 72 mm/min. Reasoning: the formula converts surface speed to rotational speed for that diameter; feed rate then follows from revolutions per minute.
Traps
Mixing mm and m in the speed formula; drilling without a centre drill; leaving a chuck key in place; using a lathe tool below centre; forcing a blunt drill.