How to measure with a micrometer
In this lesson, we take a closer look at how to measure with a micrometer.
Micrometers are more accurate than vernier calipers. Using them does take a feel, and setting them up correctly can make all the difference to your results.
Digital or Mechanical Micrometers
The first choice you need to make is the size micrometer you need. Micrometers have a short range of measurement, and you need to know how big the part is that you are planning to measure. It is no good if the part will not fit within the arms of the measuring tool.
The next question is digital or mechanical readout. A digital micrometer is easier to read, but it uses batteries that can be flat when you need them most. Another big advantage of digital over mechanical is that you can swap between metric and standard at the press of a button. If you get a mechanical caliper, it will be either metric or standard, and you will have to use math to convert the readings.
To read a mechanical micrometer, you will set the large whole number on the inner shaft. Then the numbers on the outer shaft will be less than whole numbers. Watch the video to see this in action. We primarily use metric tools because the car we work on a measured in metrics.
Zeroing a micrometer
Most micrometers will come with a calibrated piece to check zero. By closing the tool on this part and leaving it movable, you will know where your micrometers are starting from. Remember not to crank down so hard you either crush the part or force the micrometer out! Temperature can also be a factor, so use the insulated parts to handle the micrometer and zero parts. Keeping the micrometer clean is very important as well.
When you use a digital micrometer, resetting zero is just a press of a button. Always ensure the contact points are clean and you are good to go. If your mechanical micrometer is out of zero, you must move it manually. Each tool should come with a small wrench to get the job done. Again, make sure it is all clean before you re-zero.
Measure with a micrometer in the real world
As I said earlier, you need a variety of micrometers as they do not have a large range of measurement. So with the correct range micrometer, you can practice measuring. To start with, grab a gauge block with a set size. By practicing measuring this block, you can see if you come up with the same number.
You can use a micrometer as a comparative measuring tool. By setting the known size as zero and then comparing the parts. They will plus or minus the set size.
Now that you can accurately measure flat objects, it is time to try something round. Some kits come with a small ball to put on the end of the measuring arm. This will decrease the contact area and help you measure a rounded item. Practicing with known sizes is the best way to get the feel for it.
We need to use a micrometer when a vernier measurement is not accurate enough. That means out to three decimal places. A good example is crankshaft bearings. The difference between the standard and oversized bearings is .025mm, and this is just not possible to measure with vernier calipers.
Don’t forget to check out our other automotive fundamentals: