Manufacturing
Metrology & Measurements
5 self-contained study topics — notes, diagrams, formulas, and worked examples for exams and GATE.
Topics
- Standards and LimitsThe limits-and-fits system fixes tolerances from the fundamental tolerance unit i = 0.45∛D + 0.001D (µm); IT grades scale this unit. Hole-basis and shaft-basis systems define clearance, transition, or interference fits, per PN Rao.
- Linear and Angular MeasurementLinear instruments (vernier, micrometer) resolve to their least count = main-scale division/number of vernier divisions; angular measurement uses sine bars and bevel protractors. Slip gauges provide length standards, per PN Rao.
- Comparators and GaugesComparators magnify small deviations from a set standard; amplification = pointer movement/plunger movement. Limit gauges (GO/NO-GO) check whether a part lies within tolerance without measuring size, per PN Rao.
- Surface RoughnessSurface roughness is quantified by the arithmetic mean deviation R_a = (1/L)∫|y|dx and the RMS value R_q. It affects friction, wear, fatigue, and sealing, per PN Rao.
- Statistical Quality ControlSQC monitors a process with control charts: X̄ chart tracks the mean, R chart the spread, using control limits at ±3σ. Process capability C_p = (USL − LSL)/6σ compares tolerance to spread, per PN Rao.