Vernier calipers are often employed in industry as a tool for measuring length.
They can directly measure high-precision parts such as part length, inner diameter, outer diameter and depth.
Vernier Calipers Overview
As a widely used high-precision measuring tool, calipers consist of a main scale and a vernier that slides on the main scale. Depending on the value of the scale on the vernier, calipers can be divided into three types: 0.1, 0.05 and 0.02 mm.
Vernier caliper reading method
Taking an accurate Vernier caliper with a scale value of 0.02 mm as an example, the reading method can be divided into three steps:
1) The entire millimeter value is read based on the closest scale on the main ruler to the left of the zero line of the vernier scale.
2) The decimal value is read by multiplying the number of scales aligned on the main ruler to the right of the zero line of the vernier scale by 0.02.
3) The final measurement is obtained by adding the integer and decimal parts detailed above.
Method of reading a 0.02 mm Vernier caliper.
As shown in the figure above, the zero line of the vernier scale corresponds to the 64 mm mark on the main scale. The ninth line behind the zero line of the vernier scale aligns with a scale line on the main scale.
The ninth line behind the zero line of the vernier scale represents: 0.02×9= 0.18mm;
Therefore, the dimension of the measured part is: 64+0.18=64.18mm.
Instructions for Using a Vernier Caliper
Align the jaws and check that the zero mark on the vernier is aligned with the zero mark on the main scale. If it is aligned, you can proceed with the measurement. Otherwise you need to observe zero error.
If the vernier zero mark is to the right of the zero mark on the scale body, it is considered a positive zero error. If it is to the left, it is a negative zero error (this rule is in line with the convention for number lines, where points to the right of the origin are positive and those to the left are negative).
During measurement, hold the scale body with your right hand and move the vernier with your thumb.
Hold the object to be measured (whether its outer or inner diameter) with your left hand, positioning it between the outer measuring jaws. When the object fits tightly into the jaws, you can read the measurement, as shown in the figure below:
Vernier Caliper Applications
Vernier calipers, as a commonly used measuring tool, can be specifically applied to the following four areas:
1) Measure the width of the workpieces
2) Measurement of the outer diameter of the parts
3) Measurement of the inner diameter of the parts
4) Depth measurement of workpieces
See the figure below for specific measurement methods for these four areas:
Usage precautions
The Vernier caliper is a highly accurate measuring instrument. Certain precautions must be taken during its use:
1. Before use, clean the measuring surfaces of both jaws. Close the jaws and check that the zero line of the vernier scale is aligned with the zero line of the main scale. If it is misaligned, adjust the measurement reading according to the original error.
2. When measuring a workpiece, the measuring surfaces of the jaws must be parallel or perpendicular to the surface of the workpiece. Avoid tilting and excessive force to prevent the jaws from deforming or wearing out, which may affect measurement accuracy.
3. When reading the calibration, your line of sight should be perpendicular to the scale surface. Otherwise, the measurement value may be inaccurate.
4. When measuring the inner diameter, gently shake the caliper to find the maximum value.
5. After using the Vernier caliper, clean it thoroughly, apply protective oil, and store it inside a box to prevent rust or bending.
The micrometer, also known as the screw gauge, is another precise measuring instrument. The principles, structure and methods of using the micrometer will be explained below.
What is a micrometer?
A micrometer, also known as a screw micrometer or caliper, is a tool for measuring length with greater precision than a caliper.
It can measure lengths with an accuracy of 0.01 mm, with a measuring range covering several centimeters.
The structure of a micrometer
Below is a schematic diagram of the structure of a micrometer:
Working Principle of Micrometric Screw Gauge
The micrometer screw gauge is manufactured based on the principle of helical amplification, that is, when a screw rotates one full turn in the nut, it advances or retreats a distance of one step along the direction of the axis of rotation.
Thus, a small distance moved in the axial direction can be represented by readings on the circumference.
The precision micrometer thread has a pitch of 0.5 mm and the sliding scale has 50 subdivided scales. With one full rotation of the sliding scale, the micrometer screw can move forward or backward by 0.5 mm.
Therefore, each small subdivision rotation is equivalent to the advance or retreat of the micrometer screw of 0.01 mm (0.5/50). It is clear that each small division on the sliding scale represents 0.01 mm, so the micrometer can measure accurately up to 0.01 mm.
As it can read to the thousandth of a millimeter, it is also known as the thousandths ruler.
How to use the screw micrometer
When we frequently help customers connect our data acquisition device to screw micrometer for high-efficiency measurements, we normally instruct them to adhere to the following points:
1. Before use, check the zero point: Slowly turn the fine adjustment knob D′ to make the measuring rod (F) and measuring anvil (A) come into contact until you hear a click. At this point, the zero marking on the movable sleeve must be aligned with the baseline (long horizontal line) on the fixed sleeve, otherwise there is a zero error.
2. Hold the caliper (C) in your left hand and, with your right hand, turn the coarse adjustment knob (D) so that the distance between the measuring rod (F) and the anvil (A) is slightly greater than the object to be measured. Insert the object and turn the lock knob (D') until the object is locked and the ratchet makes a sound. Once the measuring rod is secured by manipulating the lock button (G), take the reading.
Reading method for micrometer screw gauge
1. First read the fixed scale.
2. Then read the half scale. If the half-scale line is visible, record it as 0.5 mm; if it is not visible, record it as 0.0 mm.
3. Then read the sliding scale (considering estimated readings), recorded as n×0.01mm.
4. The final reading is the sum of the fixed scale, the half scale and the moving scale.
Since the reading result of the micrometric screw gauge is accurate to the thousandth place in millimeters, it is also known as a micrometer.
Things to Watch Out for with the Micrometer Screw Gauge
1. When measuring, be sure to stop using the button when the micrometer screw is close to the object being measured. Use the fine adjustment knob to avoid excessive pressure. This will ensure accurate measurements and protect the micrometer screw gauge.
2. When reading the scale, pay attention to whether the line representing half a millimeter on the fixed scale is visible.
3. During reading, the thousandths place has an estimated digit that should not be disregarded, even if the zero point of the fixed scale is aligned with a certain line of the moving scale. The thousandths place should still be read as “0”.
4. When the anvil and micrometer screw are closed together, if the zero point of the moving scale does not coincide with the zero point of the fixed scale, a zero error will occur. This must be corrected by subtracting the zero error value from the final length reading.
Proper use and maintenance of the micrometer screw gauge
• Check the accuracy of the zero mark;
• Make sure that the surface of the part to be measured is clean;
• For larger pieces, use a V-block or flat plate for measurement;
• Clean the measuring rod and anvil before measuring;
• Use a ratchet to adjust the thimble;
• Avoid loosening the rear cover to avoid altering the zero mark;
• Do not introduce common machine oil between the fixed and mobile sleeves;
• After use, clean and lubricate the micrometer, store it in the designated box, and store it in a dry place.
