Using a dial gauge involves proper setup, calibration, and precise measurement to determine small variations in a surface or part with high accuracy. This instrument is essential for tasks requiring the measurement of flatness, runout, depth, or concentricity.
Understanding Your Dial Gauge
Before diving into the steps, it's crucial to familiarize yourself with the parts and specifications of a dial gauge.
- Components: A standard dial gauge consists of a main body, a plunger (or spindle) that moves up and down, a dial face with a needle, and a rotating bezel.
- Specifications: Usually, the specification for the dial gauge will be on the face of the gauge. This includes its measuring range (e.g., 0-10 mm) and its least count or resolution (e.g., 0.01 mm, meaning each small division represents 0.01 mm). Understanding these values is critical for accurate readings.
Step-by-Step Guide to Using a Dial Gauge
Follow these steps for effective and precise measurement with a dial gauge:
Step 1: Preparation of the Workpiece and Gauge
Thorough preparation is the foundation of accurate measurement.
- Cleanliness: Ensure both the workpiece and the measurement surface of the dial gauge are free from dirt, dust, oil, or burrs. Even a tiny particle can significantly affect the reading.
- Stability: Place the workpiece on a stable, flat surface, such as a granite surface plate, to eliminate any movement during measurement. The dial gauge stand itself must also be firm and vibration-free.
Step 2: Mounting the Dial Gauge
Proper mounting ensures consistent and reliable contact.
- Secure Attachment: Attach the dial gauge securely to its stand, typically a magnetic base stand or a universal stand. The stand provides the necessary stability and flexibility to position the gauge.
- Positioning: Position the gauge so that its plunger is perpendicular to the surface you intend to measure. Angled contact can lead to cosine error, resulting in inaccurate readings. Ensure the plunger has sufficient travel distance in both directions from the expected measurement point.
Step 3: Setting the Dial Gauge to Zero
Zeroing the gauge establishes a reference point for measurement.
- Initial Contact: Gently bring the dial gauge's plunger into contact with the reference surface or a known datum point on your workpiece. Ensure there is a slight pre-load on the plunger, meaning it's depressed a little beyond its free state.
- Rotate Bezel: While the plunger is in contact with the reference, rotate the outer bezel of the dial gauge until the main needle points exactly to the "0" (zero) mark. This establishes your baseline.
Step 4: Taking the Measurement
Once zeroed, you can proceed with measuring variations.
- Movement: Carefully move the workpiece underneath the dial gauge's plunger, or move the dial gauge over the surface to be measured.
- Observe Needle: As the plunger moves up or down in response to surface variations, the needle on the dial face will move. For instance, when the needle moves, this much we are moving approximately point two of a millimeter. This indicates a change of 0.2 mm from your zero reference.
- Record Readings: Note the highest and lowest readings indicated by the needle. If the needle moves clockwise from zero, it typically indicates a higher point (positive deviation); if it moves counter-clockwise, it indicates a lower point (negative deviation).
Step 5: Interpreting Readings
Understanding the needle's movement relative to the zero point is crucial.
- Deviation: The total deviation is the difference between the maximum and minimum readings observed. For example, if the needle moved from -0.05 mm to +0.10 mm, the total variation is 0.15 mm.
- Range and Least Count: Always refer back to the gauge's specifications on its face to correctly interpret the scale. If your gauge has a least count of 0.01 mm, each small mark on the dial represents 0.01 mm.
Common Applications of Dial Gauges
Dial gauges are versatile tools used in various industries for quality control and inspection:
- Runout Measurement: Checking the eccentricity or "wobble" of rotating shafts, brake rotors, or gears.
- Flatness Inspection: Verifying the flatness of surfaces like engine blocks or machine beds.
- Depth Measurement: Determining the depth of grooves or steps.
- Parallelism Checks: Ensuring two surfaces are parallel to each other.
- Concentricity Testing: Assessing how well two cylindrical features share a common axis.
Tips for Accurate Measurement
- Temperature Stability: Perform measurements at a stable ambient temperature, as temperature fluctuations can affect the dimensions of the workpiece and the gauge.
- Consistent Pressure: Ensure consistent contact pressure if manually holding the gauge, although a proper stand minimizes this concern.
- Minimize Parallax Error: Always view the dial face straight on to avoid reading errors due to parallax.
- Regular Calibration: Calibrate your dial gauge periodically against known standards to ensure its accuracy.
