Reading a Standard Micrometer.mp4

Micrometers are used everyday by mechanics to measure wear on the parts. Having the ability to read them quickly and accurately is important for the mechanic. There are two types of standard micrometers. The standard micrometer can measure to within one thousandths of an inch and the Vernier micrometer can measure to within ten thousandths of an inch.

Choosing which micrometer depends on the accuracy you desire.  For this lesson, we'll focus on the Vernier micrometer to make measurements within one ten thousandths of an inch. The major parts of an outside micrometer are: Before using a micrometer, make sure the ends of the measuring surfaces are clean and that the micrometer is properly calibrated. Use a piece of paper or cloth and clean the measuring faces thoroughly.

Check the calibration of the micrometer by using the ratchet to close the measuring ends and checking to see if the zero line on the sleeve is lined up with a zero line on the thimble. Use a spanner wrench in the small hole on the sleeve and turn the sleeve until both zeros line up. There are 40 equal lines on the sleeve and each line represents 25 thousandths of an inch.  Every fourth line is a little longer and represents hundred thousandths of an inch.

For example, the line marked 1 represents one hundred thousandths of an inch and the line marked 2 represents two hundred thousandths of an inch. The beveled edge of the thimble is divided into 25 equal parts, with each part representing one thousandth of an inch. When the thimble is turned one complete revolution, it advances the spindle in or out 25 thousandths of an inch. To read a Vernier micrometer, first add up all the numbers to the left of the thimble.

Using this picture as an example, the largest number to the left of the thimble is 1. Write this down as 100 hundred thousandths of an inch. Now, count how many 25 thousandths lines there are between the large number 1 and the thimble.  As you can see that there are three short lines showing, write this down as 75 thousands of an inch.

The next step is to read the thimble. Look at the thimble and see what number lines up with or are just below the line on the sleeve. This is written as 9 thousandths of an inch. The last step is to read the Vernier scale.

Find the line on the Vernier scale that lines up with the line on the thimble and write down this number. Do not write down the number on the thimble. Add up all the numbers you wrote down and this will tell you what the micrometer reads. In this example, the measurement is 1,844 ten thousandths of an inch.

In this example, the number 3 is to the left of the beveled edge. This is written as 300 thousandths of an inch. There are two quarter lines and two times 25  thousands equals 50 thousandths of an inch. The thimble line just below the sleeve zero line is 6.

One cannot count the number 7 since it has not come around yet. This is written as 6 thousandths of an inch. The 6 line on the Vernier scale is lined up with the line on the thimble and this is written as 6 ten thousandths of an inch. The total measurement is 3,566 ten thousandths of an inch.

In this example, the 4 is to the left of the thimble. The number 5 line is visible, but cannot be counted since the zero line on the thimble has not come around and lined up with the sleeve zero line. There are three quarter lines and three times 25 thousands equals 75 thousandths of an inch. The thimble line just below the sleeve zero line is 24 thousandths of an inch.

The 4 line on Vernier scale is lined up with the line on the thimble and is written as 4 ten thousandths of an inch. The total measurement is 4,994 ten thousandths of an inch..