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Lesson 09 'සම්මත මිණුම් හා උපකරණ' (Standard Measurements & Instruments) හි ප්‍රධාන මාතෘකා:

• 📐 SI Units — Length (m), Mass (kg), Time (s), Temperature (K), Current (A)
• 🔢 Vernier Caliper — reading method, Least Count = 0.02 mm
• 🔩 Micrometer Screw Gauge — external/internal, LC = 0.01 mm
• 🎯 Dial Test Indicator (DTI) — runout, flatness measurement
• 🧊 Slip Gauges & Limit Gauges (Go / No-Go)
• 🔬 Surface Finish — Ra value, roughness symbols
• ⚙️ Tolerance, Limits & Fits — Clearance, Interference, Transition
• 📏 Angular Measurement — Sine Bar, Protractor, Clinometer, Comparators

Vernier Caliper Reading Steps:

• Step 1 — Main Scale: Vernier zero point ට left side ඇති last mm value ගන්න
• Step 2 — Vernier Scale: Main scale line සමඟ align වන vernier line number × LC
• Step 3 — Total = Main Scale + (Vernier number × Least Count)

LC = 1 MSD − 1 VSD  |  Standard: 50 div → LC = 0.02 mm

Example: Main = 23 mm + Vernier 14th line → 14 × 0.02 = 0.28 mm → Total = 23.28 mm

AL Tech Hub (altechhub.lk) හි Lesson 09 Downloads කොටසෙන් නොමිලේ ලබාගත හැකිය:

• 📄 Full Notes PDF — 6.5 MB, 90 pages
• 📄 Measuring Instruments Guide — 2.8 MB, 28 pages
• 📄 Vernier & Micrometer Practice — 2.0 MB, 20 pages
• 📄 Tolerance & Fits Reference — 1.8 MB, 18 pages
• 📄 Surface Finish Standards — 1.5 MB, 14 pages
• 📊 Slide Deck (PPTX) — 8.5 MB, 56 slides
• 📝 Practice Q&A (DOCX), Past Papers, 🗜️ Complete Bundle (ZIP 28 MB)

Tolerance = Upper Limit − Lower Limit (permissible variation)

Fits වර්ග:

• Clearance Fit — shaft < hole (bearings, sliding parts)
• Interference Fit — shaft > hole (press fit, permanent assembly)
• Transition Fit — clearance or interference (locating fits)

H7/h6 — H = Hole (uppercase) · h = Shaft (lowercase) · 7/6 = IT grade

Example: 25H7/h6 = 25mm nominal, H7 hole, h6 shaft → clearance fit