How to use a dial indicator?

A dial indicator, also known as a dial gauge, is a precision measuring instrument used to accurately measure small linear distances, surface variations, or deviations in mechanical components. It's a fundamental tool for ensuring accuracy and quality in manufacturing, machining, and engineering.

Understanding the Dial Indicator

A dial indicator typically consists of a plunger or spindle that moves linearly, which in turn rotates a needle on a graduated dial face. This allows for precise measurement of very small displacements.

Key Components

Plunger/Spindle: The movable rod that contacts the surface being measured.
Dial Face: The main scale with graduations, usually in thousandths of an inch or hundredths of a millimeter.
Main Needle: The large needle that indicates the precise measurement on the dial face.
Revolution Counter (Small Dial): A smaller, inner dial that counts the total number of revolutions made by the main needle, indicating larger displacements. For example, on some indicators, 10 revolutions of the main needle can equate to 10 millimeters of total travel, as tracked by this smaller counter.
Bezel: The outer ring of the dial, which can be rotated to set the zero point.
Stem: The cylindrical part used for clamping the indicator to a stand.
Contact Point: The tip of the plunger that touches the workpiece, often interchangeable.

Setting Up Your Dial Indicator

Proper setup is crucial for accurate readings.

Mounting the Indicator

Choose a Sturdy Stand: Use a magnetic base stand or a rigid clamping stand to hold the indicator securely. Any movement in the stand will compromise accuracy.
Position the Indicator: Attach the indicator's stem to the stand.
Perpendicularity: Ensure the plunger is as perpendicular as possible to the surface being measured. Angled contact can introduce errors.
Preload the Plunger: Gently lower the indicator so the plunger is slightly depressed (preloaded) against the workpiece. This ensures the plunger is always in contact and moving within its operational range, preventing backlash or inconsistent readings.

How to Use a Dial Indicator for Measurements

Using a dial indicator involves establishing a reference point and then measuring deviations from that point.

Common Measurement Applications

Here's how to use a dial indicator for some of its most common applications:

1. Measuring Runout (Concentricity/Wobble)

Runout refers to the deviation from perfect concentricity or parallelism of a rotating part.

Setup: Mount the part securely in a lathe, V-block, or fixture. Position the dial indicator's contact point against the surface to be measured (e.g., the outside diameter of a shaft, the face of a flange).
Zeroing: Rotate the part slowly to find the highest or lowest point. Rotate the bezel to set the main needle to zero at this point.
Measurement: Slowly rotate the part through a full 360 degrees. Observe the total travel of the main needle. The difference between the highest and lowest readings is the total indicator reading (TIR), representing the runout.
- Example: If the needle moves from 0 to +0.003" and then to -0.002", the TIR is 0.003" - (-0.002") = 0.005".

2. Measuring Flatness or Parallelism

Setup: Place the workpiece on a known flat surface plate. Mount the dial indicator on a surface gauge or granite surface plate stand.
Zeroing: Gently bring the contact point down onto the workpiece. Slide the indicator across the surface, noting the high and low points. Rotate the bezel to set the main needle to zero at your chosen reference point.
Measurement: Carefully glide the indicator across the entire surface of the workpiece. Observe the maximum deviation from your zero setting. The total range of movement indicates the flatness or parallelism error.
- Insight: For large surfaces, grid patterns can be used to ensure comprehensive measurement.

3. Setting a Reference Height or Depth

Setup: Position the dial indicator so its contact point rests on a known reference surface (e.g., machine table, gauge block).
Zeroing: Rotate the bezel to set the main needle to zero.
Measurement: Lift the indicator, place the workpiece under the contact point, and gently lower the indicator onto the workpiece. The reading on the dial will indicate the height difference between the workpiece and the reference surface.
- Practical Use: This is often used for setting tool heights or checking component dimensions relative to a datum.

Reading the Dial Indicator

Understanding how to read both the main dial and the revolution counter is essential for accurate measurements:

Main Dial: Each graduation on the main dial represents a small unit of measurement (e.g., 0.001 inch or 0.01 mm). The main needle's position indicates the precise value within a single revolution.
Revolution Counter (Small Dial): This smaller, inner dial keeps track of the total number of full rotations the main needle has made. If the main needle completes a full revolution, the revolution counter will advance by one mark. This is crucial for measuring displacements greater than one full sweep of the main dial. Always note the revolution counter for total travel, especially when measuring over a larger range.

Tips for Accuracy and Best Practices

Cleanliness: Always ensure the workpiece, indicator contact point, and measuring surfaces are clean and free of debris.
Temperature Stability: Allow components to stabilize at room temperature, as thermal expansion can affect measurements.
Consistent Pressure: Apply consistent, light pressure when preloading the plunger.
Proper Lighting: Good lighting helps in accurately reading the dial.
Minimize Parallax Error: View the dial face directly from above to avoid misreading due to angle.
Check Calibration: Periodically verify the accuracy of your dial indicator using gauge blocks or certified masters. Reputable sources like Mitutoyo's guide to measurement offer valuable insights into maintaining accuracy.

Maintenance of Your Dial Indicator

Storage: Store the indicator in its protective case when not in use to prevent damage.
Cleaning: Wipe the stem and plunger with a clean, lint-free cloth. Avoid using harsh solvents.
Lubrication: Do not lubricate the internal mechanisms unless specifically recommended by the manufacturer.
Handling: Handle with care; dropping can severely impact its accuracy.

Common Dial Indicator Applications

Application	Purpose	Key Consideration
Runout Measurement	Checking concentricity or wobble of rotating parts	Ensure part is securely mounted and rotates smoothly.
Flatness/Parallelism Check	Assessing surface evenness or parallel alignment	Use a calibrated surface plate as a datum.
Depth/Height Comparison	Determining differences in vertical dimensions	Establish a reliable zero reference point.
Axial Play Measurement	Checking end play or movement along an axis	Apply consistent force to the component during measurement.
Machine Alignment	Ensuring components of machinery are correctly aligned	Check multiple points and axes for comprehensive results.