What Is A Micrometer?

Alliance Calibration specializes in multiple types of calibration, including mechanical calibration which services a number of different mechanical instruments. One of the most common mechanical instruments that we receive for calibration is the micrometer.

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What is a micrometer?


A micrometer is an instrument designed to take very precise measurements of vary small items and spaces, like screws, pipes, valves, and tools. Generally, micrometers are used by people who need to get extremely accurate measurements that are very important in mechanical engineering. In these instances, measurements that are even slightly off could cause minor to serious problems.


Micrometers come in a variety of sizes to fit a range of mechanical parts and fittings, although most of them are made to measure within one-thousandth of an inch. There are serveral different types of micrometers, as well, which let you measure the different spaces of varying objects.

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Outside micrometer


If you want to measure the thickness or diameter of a tiny part or fitting, you will need an outside micrometer. Outside micrometers offer extreme accuracy for these types of measurements. Their consistency, straightforward design, and ease of use have made them an industry standard measuring tool.


An outside micrometer looks a little like a hook with the measuring faces — an anvil and a spindle — connecting the opening. To measure a part’s thickness, you would place it in between the anvil and spindle, and then turn the thimble at the other end of the device. The thimble advances the spindle until it stops at the part, and a ratchet stop ensures even measuring pressure. At this point, you can read the measurement off of the micrometer.


Outside micrometers come in different designs that make them easier to measure items in hard-to-read places. They are available in both digital and mechanical forms. No matter which type you’re using, it’s important to keep the measuring faces flat and parallel, or else the measurements will not be accurate.


Inside micrometer


There are a few different versions of an inside micrometer, which is used to measure the interior diameter of an item.


One model of the inside micrometer resembles the outside micrometer in that it also has a thimble and ratchet for turning the spindle, and a sleeve with the measurements marked on it. However, instead of having the hook that can hold an item inside of it, these inside micrometers feature tiny carbide jaws. These are placed inside of an object and adjusted by the spindle until they reach the object’s full width. This provides precise measurement for the inside diameter of nuts, tubes, and other mechanical pieces.


Another type of an inside micrometer looks more like a pen. You use this kind by sticking the end inside of the part you are measuring. When you turn the thimble, the micrometer dialates until both ends are touching the inside of whatever you’re measuring. You can then read the numbering system on the inside micrometer to get an accurate measurement.


Whichever type of inside micrometer you use, you’ll want to be sure your instrument is stable when you use it in order to get the most precise measurement.

 Depth gage calibration _Alliance Calibration

Depth micrometer


Depth micrometers can provide exact measurements for the depths of holes, counterbores, slots, and any distance between a surface and a recessed space.


This type of micrometers a shaped a little like a “T.” The bottom of the “T” is home to the thimble, thimble sleeve, and scale, and the top is formed of a flat base. When it’s time to measure, you’ll need to select one of several measurement rods, depending on the size of the recess you’re measuring. The measuring rod gets secured into the base, leveled with the base, and then entered into the recess that needs measured. Once it reaches the bottom of the surface being measured, you can read the measurements off of the instrument.


How to read a micrometer


Before you use a micrometer, check to see what unit of measure it uses. It’s best to find one that’s in the same units as the items you’re working with, whether that’s metric or English.


To get the measurement, use the micrometers as direct above, tightening the thimble until the instrument is as tight as possible. Next, you can get the measurement off the micrometer by adding together the numbers off of the thimble and the spindle. Each micrometer is a little different in how it’s laid out. It’s best to consult the instruction manual for your micrometer to learn exactly how to read the measurements.


When to use a micrometer


A micrometer is a necessary tool anytime you need to make a precise, mechanical measurement, whether you’re looking for the width of a pipe or the length of a bearing’s interior. Accuracy makes all the difference in mechanical engineering, where there are many moving parts that need to work together precisely. Getting an exact measurement with a micrometer can make or break projects that rely on a flawless fit. Some instances in which a micrometer could save the day include fitting pipes for moving gasses with tiny, light molecules, building machines with moving parts like a piston, or measuring the thickness of sheet metal.

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How and why to calibrate a micrometer


Having a micrometer correctly calibrated is key to its overall precision. When we calibrate an instrument, we search for errors in the measurements, and ensure that it’s providing you with the correct information.


The first step in calibrating a micrometer is looking for any signs of damage to the structure. If the spindle and anvil faces are warped at all instead of laying flat, the device will read incorrect measurements. We want to make sure the parts moving smoothly, and that everything is in working order.


Next we can move forward in using the five-point calibration method to make sure the micrometer can perform its measurements perfectly. If you want to ensure precise measurements and avoid wasting time with errors and do-overs, it’s best to have your micrometer set calibrated by a professional calibration lab.



Phil Wiseman

Phil Wiseman

Phil Wiseman is Chief Marketing Officer at Alliance Calibration. He earned a B.S. in Chemical Physics from Centre College. Phil is an ASQ Certified Quality Auditor and ASQ Certified Manager of Quality/Organizational Excellence.

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