Dial indicators are almost always used in conjunction with scales to measure small changes, such as weight and distance. But how do you read them? Dial indicators are commonly used to measure runout.
There are two types of runout.
1) axial runout and 2) radial run out
Objects that rotate in an unreal motion are considered run out. Axial Clearance is also measured by dial indicators, which describe the axial movement of objects.
Axial Run out of a Gear
The photo shows axial run out on a ring gear. In this case, the ring gear is wobbling, causing the dial to bounce back and forth.
Axial free movement measurement
Here is how to measure a gear’s axial free movement. A dial indicator measures the amount of movement between the thrust bushings of the gear.
1” Linier Dial Indicator
An indicator with a one-inch linear dial. To the right is the tip that screws onto the plunger. The dial itself has a scale and an indicator body. Above the scale lock, there is a needle that moves. Turning the outer scale for calibration is possible by loosening the scale lock.
Additionally, the range (0-1) tells us the range of the dial indicator. The 0.001 mark (zero to one inch) Range and the units of measure or accuracy. In here we can measure in inches down to 1 1000 of an inch.
.030” Dove Tail Dial Indicator
Finally, the revolution counter counts how many times the dial has actually rotated around.
This is a 30000 an inch dovetail dial indicator: we can see the mounting locations, the body, the plunger, the adapters, and the dial itself, as well as the units of measurement.
Reading the one-inch dial indicator:
The large-scale numbers are in black and range from zero to one hundred thousandths of an inch. The large scale numbers in the red range from zero to plus fifty thousand of an inch and from zero to minus fifty-thousandths of an inch.
The scale in the middle records the number of revolutions. This recorded one full revolution of the big scale for every number on the small scale. The number one one-thousandths of an inch in the middle indicates that each large scale line is equal to one one-thousandth of an inch.
When measuring a value that is greater than one full revolution on the Large Scale, we need to look at the small scale as well because that counts the number of turns.
In this example: you can see in the picture below that the small scale has actually passed the four, this indicates the large scale has circled around four times and that equals four hundred thousandths of an inch.
Now take a look at the outer scale. The black number reads twenty-thousandths of an inch. If we add both of these numbers together, we come up with the value of 420 thousandths of an inch.
Could you please tell me what this dial reads? You can see it on the indicator above if you look carefully. Have you noticed that it’s almost 400 thousandths of an inch but not quite? Let’s take a look at the bigger picture. You should get 397 thousandths of an inch when you add these two values together.
Reading the Dove Tail dial indicator:
This Dove Tail reads a maximum of thirty-thousandths of an inch, therefore we use it to measure small measurements. We use it where a linear plunger won’t work.
Take a close look at the picture. Each line measures five-ten thousand of an inch or also known as one half of one one-thousandth of an inch. even One-thousandth of an inch is equal to every two lines.
I usually count by half when reading dovetails. For example, my first measurement is going to be one half of one one-thousandth of an inch, then the next line is going to be one one-thousandth of an inch, then one and a half thousandths of an inch, then two thousand of an inch, two and a half thousandths and finally three thousands of an inch where my pointer is lined up in the picture.
Look at this reading, it is showing twelve and one-half thousandths of an inch or it could remain at 125 ten thousandths of an inch. It would be written as point zero one two five and the closing quote mark using the close quote symbol indicates Inches.
It’s imperative to understand how to read dial indicators since they measure in small increments. It is crucial to measure accurately in areas such as machine parts, where even a small error can have catastrophic results.
Reading inward plus reading outward = Total Reading
In general, you can easily read a dial indicator. To add the inner and outer scales, you just have to add their reading values.
In addition to the dial indicator parts, the inner scale represents the complete revolution of the long pointer. Meanwhile, the outer scale is the magnifying glass for each of the divisions on the inner scale
Movement is rarely measured by dial indicators, only static values.
Often the movement is less than one hundred thousandths of an inch.
Therefore, we don’t need to look at the small gauge because it is less than one full revolution and we measure total needle movement. This means we add the negative movement to the positive movement to get the total movement.
The needle moves from plus five-thousandths of an inch to minus ninety-thousandths of an inch. There are fifteen-thousandths of an inch in the entire needle movement.
The total of fifteen-thousandths of an inch are moved by the needle: ten thousandths to the negative side, followed by five thousandths to the positive side.
We can see in the video, the needle moves on the Dove Tail. It moves from four and a half thousandths of an inch on the minus side to five and a half thousandths of an inch on the minus side for a total movement of one-thousandth of an inch.
How much movement does this dial experience as it swings back and forth? If you figured it was 42 thousandths of an inch you are correct. However, how much total movement is shown here? Did you figure six and a half thousandths of an inch if so you are correct?
Conclusion Of The Reading Of Dial Indicator
In conclusion, dial indicators are a great way to measure small changes, such as weight and distance. The best way to read a dial indicator is by reading the needle from left to right, looking at the end of the needle that was originally pointing at zero.