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Screw Gauge — Complete Theory
📖 What is a Screw Gauge?
A screw gauge (micrometer) is a precision instrument used to measure small dimensions like wire diameter, sheet thickness, and ball bearings with an accuracy up to 0.01 mm.
⚙️ Principle of Operation
Based on the screw principle: one complete rotation of the thimble moves the spindle linearly by a fixed distance = Pitch. Here Pitch = 0.5 mm.
Pitch = Distance moved in one complete rotation = 0.5 mm
📐 Least Count Calculation
Least Count (LC) = Pitch / Number of divisions on circular scale
LC = 0.5 mm / 50 = 0.01 mm (10 microns)
🔬 How to Take a Reading
- Place the object between anvil and spindle.
- Rotate the thimble until it gently touches the object.
- Read the main scale (PSR) just before the thimble edge.
- Read the circular scale division aligned with the reference line.
- Total = PSR + (Circular division × LC)
Total Reading = Main Scale Reading + (Circular Scale Division × 0.01 mm)
⚠️ Zero Error & Precautions
If the zero of the circular scale doesn't match the reference line when the anvil and spindle touch, zero error exists. Always take multiple readings for accuracy.
💡 Real-World Applications
- Engineering workshops and quality control
- Measuring wire gauges, PCB thickness
- Scientific research and physics laboratories
- Manufacturing precision components
📊 Example Calculation
If PSR = 5.5 mm and Circular division = 24,
Total = 5.5 + (24 × 0.01) = 5.5 + 0.24 = 5.74 mm
✨ Try now: Insert an object and slowly rotate using the + button until it just touches — observe the precise measurement in real-time!
