Operation of Micrometer Screw Gauge SOP

22 February, 2024 admin 0 Comments

1.0 OBJECTIVE :

Micrometer Screw Gauge is made up of a main scale and a thimble scale and it is used for measuring the thickness of packaging materials like cartons, aluminum foil etc.
It can measure maximum thickness of 25.0 mm.
The thimble has a total of 50 markings representing 0.50 mm.
The smallest marking is 1 mm on the main scale (sleeve) and 0.01 mm on the thimble scale (thimble).
Least count of Micrometer Screw Gauge is 0.01 mm.

5.1 OPERATION

Set the 0 by gently moving the thimble.
In case it is not zero, then instrument has zero error which is be adjusted.
Put the object between the fix rod and movable rod and fix the object between two rods gently moving the screw.
Spin the movable rod clockwise until the spindle just meets the object.
Set the lock nut while the micrometer is still on the object to fix the position.
Note down the reading of scale as below:
- The first part is contributed by the main scale on the sleeve.
- To obtain the first part of the measurement: Look at the image image (b) you will see a number 5 to the immediate left of the thimble.
- This means 5.0 mm. Notice that there is an extra line below the datum line, this represents an additional 0.5 mm. So the first part of the measurement is 5.0 + 0.5 =5.5.
- The second part is contributed by the rotating vernier scale on the thimble.
  - To obtain the second part of the measurement: Look at the image image (b), the number 28 on the rotating vernier scale coincides with the datum line on the sleeve.
  - Hence, 0.28 mm is the second part of the measurement.
- You just have to add the first part and second part of the measurement to obtain the micrometer reading,
  - i.e., 5.5 + 0.28 = 5.78.
- Remove the object from the micrometer.
- Reset the lock nut to the unlock position.
- Keep the instrument in box after use.
- Calibration of Micrometer Screw Gauge is perform by approved outside agency on yearly basis.

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