In various contexts of sciencetechnologyand manufacturing such as machiningfabricatingand additive manufacturingan indicator is any of various instruments used to accurately measure small distances and anglesand amplify them to make them more obvious. The name comes from the concept of indicating to the user that which their naked eye cannot discern; such as the presence, or exact quantity, of some small distance for example, a small height difference between two flat surfaces, a slight lack of concentricity between two cylinders, or other small physical deviations.
The classic mechanical version, called a dial indicatorprovides a dial display similar to a clock face with clock hands; the hands point to graduations in a circular scales on the dial which represent the distance of the probe tip from a zero setting.
The internal works of a mechanical dial indicator are similar to the precision clockworks of a mechanical wristwatch, employing a rack and pinion gear to read the probe position, instead of a pendulum escapement to read time. The side of the indicator probe shaft is cut with teeth to provide the rack gear. When the probe moves, the rack gear drives a pinion gear to rotate, spinning the indicator "clock" hand. Springs preload the gear mechanism to minimize the backlash error in the reading.
Precise quality of the gear forms and bearing freedom determines the repeatable precision of measurement achieved. Since the mechanisms are necessarily delicate, rugged framework construction is required to perform reliably in harsh applications such as machine tool metalworking operations, similar to how wristwatches are ruggedized.
Other types of indicator include mechanical devices with cantilevered pointers and electronic devices with digital displays. Electronic versions employ an optical or capacitive grating to detect microscopic steps in the position of the probe.
Indicators may be used to check the variation in tolerance during the inspection process of a machined part, measure the deflection of a beam or ring under laboratory conditions, as well as many other situations where a small measurement needs to be registered or indicated. Dial indicators typically measure ranges from 0. Various names are used for indicators of different types and purposes, including dial gaugeclockprobe indicatorpointertest indicatordial test indicatordrop indicatorplunger indicatorand others.
Indicators inherently provide relative measure only. But given that suitable references are used for example, gauge blocksthey often allow a practical equivalent of absolute measure, with periodic recalibration against the references. However, the user must know how to use them properly and understand how in some situations, their measurements will still be relative rather than absolute because of factors such as cosine error discussed later.
Probe indicators typically consist of a graduated dial and needle driven by a clockwork thus the clock terminology to record the minor increments, with a smaller embedded clock face and needle to record the number of needle rotations on the main dial.
The dial has fine gradations for precise measurement. The spring-loaded probe or plunger moves perpendicularly to the object being tested by either retracting or extending from the indicator's body.
The dial face can be rotated to any position, this is used to orient the face towards the user as well as set the zero point, there will also be some means of incorporating limit indicators the two metallic tabs visible in the right image, at 90 and 10 respectivelythese limit tabs may be rotated around the dial face to any required position. There may also be a lever arm available that will allow the indicator's probe to be retracted easily.
Mounting the indicator may be done several ways. Many indicators have a mounting lug with a hole for a bolt as part of the back plate. Alternately, the device can be held by the cylindrical stem that guides the plunger using a collet or special clamp, which is the method generally used by tools designed to integrate an indicator as a primary component, such as thickness gauges and comparators.
Another option that a few manufacturers include is dovetail mounts compatible with those on dial test indicators.Chapter 4: Using the Dial Indicator
A dial test indicatoralso known as a lever arm test indicator or finger indicatorhas a smaller measuring range than a standard dial indicator. A test indicator measures the deflection of the arm, the probe does not retract but swings in an arc around its hinge point. The lever may be interchanged for length or ball diameter, and permits measurements to be taken in narrow grooves and small bores where the body of a probe type may not reach.
The model shown is bidirectional, some types may have to be switched via a side lever to be able to measure in the opposite direction. These indicators actually measure angular displacement and not linear displacement; linear distance is correlated to the angular displacement based on the correlating variables.
If the cause of movement is perpendicular to the finger, the linear displacement error is acceptably small within the display range of the dial. Cosine error is discussed in more detail below. Many are of steel alloy tool steel or HSS ; higher-end models are of carbides such as tungsten carbide for greater wear resistance. Other materials are available for contact points depending on application, such as ruby high wear resistance or teflon or PVC to avoid scratching the workpiece.
These are more expensive and are not always available as OEM options, but they are extremely useful in applications that demand them. Modern dial test indicators are usually mounted using either an integrated stem on the right of the image or by a special clamp that grabs an dovetail on the indicator body. Some instruments may use special holders. Prior to modern geared dial mechanisms, test indicators using a single lever or systems of levers were common.Reading a dial test indicator may sound simple, and once you know what you are doing in the process, it can be.
However, like all procedures in precision measurement, you want to make sure that you know the exact steps when reading a dial test indicator in order to get an accurate measurement. Dial test indicators are a common tool found in machining shops and other measurement settings. We will walk you through the process of using and reading a dial test indicator, offering you a reference guide for how it is properly done.
Before going into the actual steps of reading a dial test indicator, we want to review the specific parts so that you know what we are referring to throughout. Picture a dial test indicator head-on, looking at the dial, or dial face.
On the dial face you will find a smaller gauge know as a turn counter. At the top of the device you have the dial test indicator cap. On either side of the cap, on the exterior of the dial face, there are two limit markers. Adjacent to the right limit marker is the bezel clamp.
The bezel surrounds the dial face, and the hand or pointer is on the dial face. On the bottom of the dial test indicator you will find the stem. Midway down the stem is the spindle or plunger, and at the bottom of the stem is the contact point. Step 1 for reading a dial test indicator is to calibrate your indicator. Start by mounting the dial test indicator onto a stand. Most of these tools will come with their own stand, but you may also use another one if you have one available.
After securing the indicator to the stand, your indicator will be fully stabilized. If it is not already, you want the hand or pointer on your dial face indicator to point to zero. Adjust the face by spinning the bezel until the hand is precisely over the zero point.
Now your dial test indicator is calibrated, ensuring that there will be fewer potential errors while taking measurements.
Step 2 starts the actual measurement process for which you will need to read the output on your dial test indicator. Press the end of the spindle extension, or the contact point, against the surface of the part you are measuring. As you press the indicator against the part surface, lock the indicator into place and begin to watch the reading on the dial while rotating the part. As you rotate the part, the pointer on the indicator will move when it detects runout or surface distortion.
Step 3 involves actually reading the dial test indicator. While rotating the part, note the maximum position that the needle moves to the left of the zero point.
Then, spin the bezel such that the zero point is once again aligned with the pointer. Rotate the part again and note the maximum position that the needle moves to the right of the zero point.
This new value gives you the total amount of movement and equals the amount of surface distortion or runout present. Additionally, you may experience multiple revolutions of the hand around the dial face. You want to count the number of revolutions that occur as well as where the hand finally stops. If your dial test indicator has a small gauge or turn counter in the dial face, this will track the total number of revolutions as well.
Dial test indicators are used to test parts for runout and surface distortion. When the hand falls between two marks, it is ok to average between the two or to round up or round down depending on your regulations.
These little tools are incredibly common, and understanding the steps to use and read a dial test indicator is key. Knowing how to read a dial test indicator is important to taking and reporting accurate measurements. Home Blog.Dial indicators are measuring instruments that consist of a pointer on a dial that moves based on whatever the dial is measuring.
This is because in areas such as machine parts, an incorrect measurement by even a small amount could be disastrous. Clean the item being measured. Check the indicator and make sure that the dial reads exactly on 0 before you begin the measurement.
Pay attention to the unit of the indicator. For example, if the indicator is measuring width, it will often be in a unit such as millimeters, or mm.
The unit should be listed on the indicator. Take note of how much each line on the dial is worth. For example, on something like a dial caliper indicator, the printed numbers on the dial will range from 0 to in increments of In this case, each line on the dial is worth one millimeter. To make it easier to read, the dial will often have a longer line for the 5 mark between each printed number. Start at the first printed number behind the pointer and then count upwards. So, for example, if the first number behind the pointer is 10, then you add the lines between that number and where the pointer is to get your measurement.
Dial Caliper Quiz
Estimate for readings between lines. If the pointer is between lines on the dial, then you will have to do a little guesswork. The best way to estimate is to gauge how close the pointer is to each line. So, for example, if the pointer is just barely below the point of hitting the fourth line between the 0 and the 10 on the dial, you might estimate and write down a measurement of 3. Sam Morgan has a master's degree in environmental science and policy.
Morgan has been interested in science writing since childhood, and enjoys writing about anything relating to science since it's challenging and interesting to learn about our world. Clean and dry any parts of the dial indicator that take in data.
About the Author. Photo Credits. Copyright Leaf Group Ltd.The comparator is an instrument used for comparing the dimensions of a component with standard dimensions. There are various types of comparators available, but the dial indicator is most common. We know that a gauge consisting of a circular partitioned dial with a pointer used for comparison in calibration purposes.
So when the dial indicator has used, this type of comparison is called dial gauge. The construction of a dial indicator is shown below with a diagram. The main scale is graduated into equal divisions corresponding to a 0. A second but small dial is set in the main dial face to indicate the number of completed revolutions turned through one revolution being equivalent to 1 mm of plunger movement.
The dial indicator is mainly classified into two groups, depending upon the shape of the dial. They are generally sector shape dial Indicator and Circular shape Dial Indicator. The sector shape dial indicator is used for Extremely accurate measurement purpose, therefore it is quite limited for practical uses. The circular shape dial indicator is widely used, and it is generally seven types.
The plunger-type mechanism is generally used for maximum indicators. The principle is very simple. It has a plunger, one end of the plunger fitted with a rack and the other end fitted with a needle. And the rack is connected to a pinion. Here is a small shaft containing pinion and gear on both sides. This gear is used as amplifying media. The principle of operation of a plunger-type dial indicator is shown in fig, where it can be seen that the plunger is attached to a rack.
Meshing with a gear wheel, the straight or linear motion of the rack is converted into an angular or turning motion, the movement being magnified by using a large gear in mesh with a small gear wheel. It is the small gear wheel that is fitted to the main scale pointer shown in fig. The mechanism described above is simple, reliable and very sensitive.
However, this sensitivity means that gear care must be exercised when using a dial gauge indicator. The lever dial indicator is characterized by their lever and scroll mechanisms. A block diagram of a lever-type dial indicator is shown below. This type of dial indicator is more compact and easier to use than plunger-type dial indicators and, it is therefore quite often used. These types of dial indicators run in one direction without stopping and without any type of separation.
And the main feature is, it does not have the two sets of numbers featured on balanced reading dial indicators. It is otherwise known as counter-clockwise dial indicators. The working principle is the same as continuous dial indicators, the only difference is the numbers run in the opposite direction.
It is running in two directions, starting from a zero in the center. And Often, positive numbers are featured to the right of the zero and negative numbers to the left.The Dial Indicator has a plunger and reads how far the plunger is raised by the surface below. The Dial Test Indicator has an arm that sweeps an angle. It measures how far the arm is pushed sideways.
Mitutoyo Dial Indicator reads how far plunger moves up to nearest thousandth of an inch 0. Once again, a Dial Indicator measures how far up the plunger moves while the Dial Test Indicator measures how far the tip of a needle moves when deflected sideways. Largely because these instruments are typically used to measure relative motion, not absolutes. For example, to ensure a vise jaw is square with the travel of the machine, you would sweep the arm of a Dial Test Indicator over the jaw while moving in the direction of travel.
There are also operations where the Dial Indicator is handy. Dial Indicators are often mounted using a lug on the back. Dial Test Indicators typically mount via either a dovetail or a small shank that can go into a collet or chuck.
Mitutoyo Digital Dial Indicator. Dial Indicators are available with Digital Readouts too, but most prefer the analog dial. Dial Indicators and Dial Test Indicators are available in a variety of accuracies and styles. I have both a half thousandth 0. The most common accuracy for a Dial Indicator is 0. Check out our article for more on Cosine Error. Like what you read on CNCCookbook? Get our latest blog posts delivered straight to your email inbox once a week for free.
Home Learn Blog. Back to Homepage. Shop All Our Products. These photos should make the differences clear: Mitutoyo Dial Indicator reads how far plunger moves up to nearest thousandth of an inch 0.
Why use the Dial Test Indicator more often?The magnetic base provides a solid mount on metal surfaces. A granite base stabilizes these indicators. The extremely tight flatness tolerances of the granite allow for nearly frictionless workpiece movement and provide an accurate reference plane for inspection work. Also known as test indicators, these have a lever-style contact point that pivots as it comes into contact with a surface. They are commonly used for consistency measurements, such as detecting variations in flatness or roundness.
Contact points, adapters, backs, extension rods, clamps, and other accessories for variance indicators. Contact Us Order. Log in. Create password. To create your password, open the email from McMaster-Carr Sales. Enter your email and we will email you a link to reset your password. Email Please enter an email. To reset your password, click on the link in the email sent from McMaster-Carr. To sign in, your browser must accept cookies.
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