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A micrometer is a measuring tool that has high accuracy. There are various types of micrometers that you will see in the shop. The most common version of the micrometer is the “outside” micrometer. This tool measures the outside dimensions of an object. The object you are measuring will be inside of (or between) the measuring surfaces.
The parts of an outside micrometer:
Micrometers come in metric and standard versions.
Standard micrometers are made to measure in one inch intervals.
A typical set might have one micrometer that measures objects up to 1 inch, one that measures between 1 and 2 inches, and one that measures between 2 and 3 inches. You need a rough estimate of the size of the object you are measuring in order to pick the correct micrometer.
A standard micrometer can measure an object accurately up to 1 ten thousandth of an inch. One ten thousandth of an inch is 0.0001 as a decimal, so this means that your measurement will be accurate up to 4 decimal places.
A measurement will have five digits:
The range of the micrometer is 1 inch. The numbers on the sleeve divide the inch into TENTHS of an inch. For example, measuring to 4 represents 0.4 inches.
Each of these intervals is divided into fourths. Remember these values are a quarter of each tenth, so you get values like these.
(1/4 of 0.1 = 0.25 ˣ 0.1 = 0.025)
There is also a set of numbers on the thimble. These go from 0 to 24. These numbers represent thousandths of an inch. For example a value of 7 on the thimble represents 0.007 inches.
If the line on the sleeve does not line up exactly with a line on the thimble, it is the first thimble number that is BELOW the line on the sleeve. In the picture to the right, the thimble number is 5.
Lastly, there is a set of numbers called the Vernier scale. These are also on the sleeve. They are numbered from 0 to 9. They are made in such a way that only one line on the vernier scale will line up with a line on the thimble.
You find the two lines that line up. You read the number on the vernier scale (the thimble number is irrelevant). This is the number of 10 thousands.
In the picture on the left, the 5 on the vernier scale lines up best. So this is a value of 0.0005.
To read the micrometer:
Place the object you are measuring between the spindle and the anvil.
Turn the thimble until the object touches both surfaces (barely).
If the micrometer has a lock, you can lock the micrometer so that you can remove the object without losing the measurement.
Read the numbers on the micrometer:
1. Note the value on the sleeve (or barrel). This is the number of TENTHS of an inch.
2. Note the value on the thimble. This is the mark BELOW the line on the sleeve. This represent the THOUSANDTHS of an inch.
3. Note the value on the Vernier scale. This is the TEN THOUSANDTHS of an inch.
Add up the numbers to get the measurement.
If you are having trouble, this video will help.
EXAMPLE 1: Find the measurement. This is a 0 - 1 inch micrometer.
Number 1: The number on the sleeve is _________?
Number 1: The number on the sleeve is _________?
The thimble is past the 0.300 mark but is not quite to the 0.325 mark. So the number is 0.300.
Number 2: The number on the thimble is _________?
Number 2: The number on the thimble is _________?
The line on the sleeve lines up exactly with the 22 mark. This is a value of 0.022. Adding 0.300 and 0.022 yields 0.322.
Number 3: The number on the vernier scale is _________?
Number 3: The number on the vernier scale is _________?
The 8 on the Vernier scale lines up best. Remember to look at the Vernier scale and NOT the thimble. The value is 0.0008. The final measurement is 0.322 + 0.0008 = 0.3228.
EXAMPLE 2: Find the measurement. This is a 2 - 3 inch micrometer.
Number 1: The number on the sleeve is _________?
Number 1: The number on the sleeve is _________?
The thimble is one mark past the 4, so the value is 2.425. (The two is from the fact that it is is 2 - 3 inch micrometer)
Number 2: The number on the thimble is _________?
Number 2: The number on the thimble is _________?
The line on the sleeve is slightly above the 19 mark. We use the 19, which is a value of .019. Adding 2.425 and .019 yields 2.444.
Number 3: The number on the vernier scale is _________?
Number 3: The number on the vernier scale is _________?
The 8 on the Vernier scale lines up best. Remember to look at the Vernier scale and NOT the thimble. The value is 0.0008. The final measurement is 2.444 + 0.0008 = 2.452.
When you are confident that you have learned the material, take the 🌟 ASSESSMENT 🌟 .
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