A Dial indicator is used to measure travel. Dial indicators are used with other tools. They need to be secure to take a measurement. Learn how to set up a dial gauge to get an accurate reading.
How to Read a Dial Indicator
On a dial gauge, the markings can be in metric or standard, but with either type, you read them the same way. The outside ring shows the increments. The distance between each mark is shown on the face. And the inner ring shows how many revolutions the outside ring has made.
The outside ring on this metric dial indicator adds up to 1mm of travel, with a total of 10mm travel. You can see that the total is 10mm by how many revolutions are indicated in the small inner gauge. The dial face has the numbers marked in forward and reverse in red. This is because you can move the shaft in and out.
How to set up a dial indicator
You can use a dial indicator to see if something is running true. Or if multiple parts are the same size, or how far a part moves up or down. This can also be a measurement of how much play a part has. Measuring how much it can move back and forth against another part. The movements can be very small as each mark is 100th of an mm and a whole revolution is only one mm. You do not use a dial gauge to measure big differences!
The dial gauge must be held very firmly so it does not move with your measurement. It is best practice to also place a pre-load on the indicator shaft. That means not having the plunger at either end of its travel. You need to take note of the inner revolutions before you measure. The outside band has markers. So you can move it to mark zero after you have set it up.
Using a magnetic block clamp
Holding your dial indicator firm is a must for an accurate measurement. You can use a magnetic base to hold it firmly. The base comes with adjustable arms to position and lock in the dial gauge. The magnet base also has a V-notch to help it clamp to round objects. Like when setting up on the strut to measure brake rotor run out.
Practice makes perfect
Find a reason to use your dial indicator; Inside the bores of a carburetor on a rebuild. The brake rotor run out. The transmission shaft run out. Compare sizes of parts. We can think of many times that the setup would be worth it. Getting to know your dial gauge and how to position it for the most accurate reading of travel comes with time. Remember, as with all our fundamental lessons, practice makes perfect.