For accurate results, proper functioning and calibration of the micrometer are very necessary. If the functioning of the micrometer is not proper then the achieved results will definitely be inaccurate. Therefore, micrometers should be calibrated at a regular interval in order to ensure accuracy.
Calibration has the ability to find out errors in the micrometer. It basically starts with the proper operation of the micrometer. Therefore, the errors may be found in the anvil, spindle, ratchet, and scale.
The calibration requires some steps to be completed in order to achieve or repair the accuracy of the micrometer. The steps are listed below. You could follow it in order to get accurate results.
Step by Step
Testing Component: Overall outlook of the micrometer
Testing Method: Taking observations by using the sense of sight and the sense of touch.
Acceptable Results: The outlook of the micrometer should not seem out of place. You need to see whether all the components of the micrometer are in place or not. If there are any signs of damage then it is likely that the measurements will not be accurate.
Testing Component: Anvil and thimble.
Testing Method: By visually observing the anvil and thimble and by touching them.
Acceptable Results: In order to ensure right measurements, it is necessary that the anvil and thimble are flat and parallel surfaces without any bumps. Bumps and nicks will not secure the object properly so it will give inaccurate results. Make sure that the anvil and thimble are flat and smooth.
You may need to employ an optical flat to check whether the anvil is truly flat or not. The optical flat is an inspection instrument which is extremely flat on its surface. Therefore, its flatness is very useful to inspect the quality of the anvil. However, it only works for a kind of flat surface anvil micrometer. It doesn’t suit the rest of it.
Testing Component: Ratchet.
Testing Method: To make sure that it works properly by moving the ratchet when the micrometer is locked. The improper functioning of the ratchet can also lead to inaccurate results.
Acceptable Results: In order to ensure the right measurement, it is necessary that the ratchet is properly functional. If the ratchet doesn’t work properly then the spindle will not move properly in the desired direction. The ratchet also controls the speed at which the spindle rotates. If the spindle is difficult to turn then it will definitely not work properly. Repairment might be able to get rid of the malfunction. A ratchet that controls the speed properly and allows the spindle to move in the desired direction is needed to accurate results.
Testing Component: Measuring scale.
Testing Method: By comparing the measuring scale to a gauge block.
Acceptable Results: The first step is to check the zero of micrometers. Check the zero a few times to ensure accuracy. In order to check the scale, you need to compare different reading of the measuring scale with the gauge block.
Why are gauge blocks used for calibration of the micrometers? Gauge blocks are used because they are very accurate and they ensure the accuracy of the micrometer as well.
How to Use the Gauge Blocks?
By following steps, you will use a set of gauge blocks to calibrate the micrometer:
- You can use 5-gauge blocks of specific sizes that include 0.210, 0.420, 0.605, 0.815 and 1 inch. The use of these 5 test points will look for errors which we want to eliminate.
- You can use any shape or size of the gauge block. However, ceramic gauge blocks are better because they have lower thermal connectivity and the body heat doesn’t affect them much.
- The gauge blocks can be measured at the ends and they can also be measured from the center as well.
- While measuring the gauge blocks, it is necessary that the anvil and spindle are properly in contact with the block. There should be no bumps or nicks or else the test will not be accurate.
- Your goal is to get a consistent value. Slide the gauge block between the anvil and spindle for a few times and make sure that the measurement you are getting is the same.
- You need to take several measurements in order to confirm the results. If the micrometer fails to produce the same result then there is a chance of error.
- While taking the measurements of the gauge block, if you observe that there is some error then you need to note it down.
- Continue taking the measurements of the rest four-gauge blocks.
You also need to make sure that the anvil and spindle have parallel flat faces that provide accurate results. You can take the measurements by keeping a small sphere in between them and then moving it around. If the value you get is zero then you will know that your micrometer is calibrated.