Machining and Machine Tools: Lathe, Milling, Drilling, Shaping and Grinding
What the exam tests
Questions mix identification of machine parts and operations with simple cutting-parameter arithmetic - spindle speed from cutting velocity, feed rate, and machining time.
Core rules
- Cutting speed V = πDN/1000 (V in m/min, D in mm, N in rpm). For turning D is the workpiece diameter; for drilling and milling it is the tool diameter.
- Turning feed is in mm/rev; milling feed is mm/tooth × number of teeth × rpm.
- Machining time for one turning pass: T = L/(f × N), where L is job length plus approach and over-run.
- Lathe operations: facing, plain turning, taper turning by compound rest or tailstock set-over, thread cutting through the half-nut and lead screw. Knurling is cold forming, not cutting.
- Milling: up (conventional) milling builds chip thickness from zero to maximum and tends to lift the work; down (climb) milling starts at maximum chip thickness and needs a backlash-free table.
- Drilling: standard point angle 118° for general steel. Reaming removes only 0.1–0.3 mm to correct size and finish, not position.
- Shaping: the quick-return mechanism makes the return stroke faster than the cutting stroke; stroke length is set by ram position and crank radius.
- Grinding wheel marking, e.g. A 46 K 5 V, gives abrasive, grit size, grade, structure and bond in that order.
Worked example
A 50 mm diameter mild-steel bar is turned at 30 m/min. N = 1000 × 30/(3.14 × 50) ≈ 191 rpm. With feed 0.2 mm/rev and a pass of 100 mm job plus 20 mm approach and over-run, T = 120/(0.2 × 191) ≈ 3.1 min.
Traps
- Substituting radius for diameter in πDN.
- Adding over-run at one end only.
- Mixing feed per tooth with feed per revolution.
- Listing knurling or reaming as lathe cutting operations.