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MICROMETER

MICROMETER

• Primarily used to measure external dimensions like diameter of sha^5 /wire, thickness of parts etc.
• Micrometer is an instrument for precise measurement of small distances.

Parts and their func/ons:

Anvil:

• Small sta>onery cylindrical part located in far end of the frame.
• Acts as one holding point for measuring objects.

Spindle:

• Cylindrical long movable part that has connec>on with ratchet.
• As we rotate ratchet counterclockwise/clockwise , spindle slides inwards/outwards.

Anvil face and Spindle face:

• Faces of both anvil and spindle which are opposite to each other.
• These are measuring points of micrometer. They hold measuring objects collec>vely.

Working Principle of Micrometer

• The amount of rota>on of the screw can be directly and precisely related to a certain amount of axial movement (vice-versa), through a constant known as the screw’s lead or pitch.
• Micrometer works on the principle of screw and nut to amplify small distances. A screw’s lead or pitch is the distance it moves forward axially with one complete turn (360 °)

Least count of a Micrometer:

• The linear distance moved by a screw is directly propor>onal to the rota>on given to it.
• The linear distance moved by the screw when it is rotated by one division of the circular scale is the least distance that can be measured accurately by the instrument. Least Count = Pitch No. of Divisions on Circular Scale For a micrometer with the pitch of 0.5 mm and 50 divisions on the circular scale. Least Count (LC) = 0.5/50 = 0.01 mm This is the smallest length one can measure with this micrometer.

Example:

How to Read a Micrometer?

Step-1 : Taking the Linear Scale Reading

• The division on the linear scale which is close to the circular scale is linear scale reading.

Step-2 : Taking the Circular Scale Reading

• The division of circular scale which considers the main scale line is reading of circular scale.

Step-3 : Final Reading

Total Reading = Linear Scale Reading + (Circular Scale Reading X Least Count) Least Count = 0.01 mm Linear scale reading = 8 mm Circular scale reading = 12 The final reading is = 8 + 12 * 0. = 8.12 mm 8 mm Circular scale reading = 12