How to Use and Read an Outside Micrometer
Machinists, manufacturing and engine professionals use an outside micrometer to measure the outside diameter of a cylindrical or spherical object to one ten-thousandth of an inch (.0001). Micrometers typically measure in ranges of 1” . In this particular example, the micrometer measures the range from 2" to 3”. This instrument is highly heat sensitive and should be stored at room temperature and so should the object being measured otherwise the reading could be wrong. When storing the measuring contacts points should be left away from each other (open) so that temperature variations do not stress the device.
[edit] Steps
Measuring
- Become familiar with the anatomy of a micrometer. The following numbers correspond to the diagram in the introduction.
- Ratchet stop
- Thimble
- Thimble scale
- Stock
- Thimble lock
- Spindle
- Anvil
- Body
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Place the object between the anvil and spindle.
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Spin the ratchet stop until the spindle meets object.
- Spin ratchet stop until you hear 3 clicks.
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Verify both the anvil and spindle are touching the object evenly.
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Set the thimble lock while the micrometer is still on the object.
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Remove the micrometer from the object once it's been locked.
Reading (Inch-System)
- Note that the measurement will start with the whole number 2.___”
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Look at the 100 thousandths markings in the stock (2.5).
- Look at individual 25 thousandths markings exposed next to the 100 thousandths, i.e. after the 5 (.25).
- Find the number and corresponding marking on the thimble scale closest to but underneath the measurement line on the stock (20).
- Add that number to the 25 thousandths marking (20 + 25), measurement should read so far 2.545.
- Flip the micrometer over to read to the 10 thousandths marking.
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Locate the marking on the stock that is inline with the marking on the thimble (4), final measurement should now read 2.5454.
[edit] Tips
- Practice -- you will develop a "touch" or "feel" for it.
- Measure the desired object multiple times as a check on your work.
- Remember also that an outside micrometer, when used correctly, is much more accurate than calipers.
[edit]Warnings
- It is assumed when a micrometer is used, that an accurate and precise measurement is desired. Ensure your micrometer is properly calibrated. They do lose accuracy with use, and must be adjusted every 36 months according to NIST. Check more often when frequently used.
[edit] Things You'll Need
- Micrometer
- Micrometer tools:
- Standard – The standard is an item of precisely calibrated length and flatness which is used to verify the accuracy of the micrometer or to reset it if it is found to be inaccurate. Standards are typically a round or rectangular piece of steel. They are employed just prior to using a micrometer or may be used on a set schedule as part of a calibration program.
- Wrench – insert in hole on back of the stock to adjust the micrometer if needed.
