Micrometer Lesson – How to measure internal dimensions correctly?

After choosing the right internal micrometer, it is also very necessary to use the micrometer correctly, which will directly affect

the accuracy and reliability of the measurement results. Today, we will take a look at the key points to pay attention to in the

measurement of internal dimensions.

Ⅰ. Preparation

1. Observe the appearance of the micrometer and check for defects such as rust, wear, and blurred readings

that affect the measurement.

2. Rotate the coarse adjustment and fine-tuning parts to ensure flexible rotation without jamming.

3. Check that the locking screw stops are reliable.

Ⅱ. Measurement

1. Determine the direction of measurement

In the length direction, the measuring jaw is parallel to each other, so when the internal micrometer is used to measure

the inner size, the measuring claw should first be fully in contact with the measured inner shape.

2. Look for the sweet spot to measure

When measuring internal dimensions with an internal micrometer, the optimal measurement value is read differently

depending on the measurement object.

• Measure the size of the hole (Figure 1)

If there is a deviation (X) between the measurement orientation (L) of the micrometer and the measured size (D),

the measurement error will be: δ=D-L=D-√￣D²-X²

Therefore, the maximum value read when measuring the bore size is the best value measured.

• Measure the width dimension (Figure 2)

If there is a deviation (X) between the measuring orientation (L) of the micrometer and the measured size (D),

the measurement deviation that occurs is: δ=L-D=D-√￣D²+X²-D

Therefore, the minimum value read when measuring the width dimension is the best value measured.

Ⅲ. Precautions

1. Avoid errors: Do not touch the measuring head directly with your hands, so as not to leave fingerprints and sweat stains,

causing rust and measurement errors. Before measuring, make sure that the inner hole surface of the object to be measured

is clean and free of impurities.

2. Correct use: When measuring, keep the inner diameter micrometer perpendicular or parallel to the measured object to avoid

measurement errors caused by angle deviation.

After use, wipe off the dirt in time, apply anti-rust oil, and store it in a special box to avoid direct sunlight and magnetic field.

3. Regular calibration: Calibrate the internal micrometer regularly to ensure its measurement accuracy.

With the above steps and precautions, you can ensure that the internal dimensions are measured correctly with an internal

micrometer and that accurate measurement results are obtained.