Bore gages measure the internal diameter of holes, cylinders, and bores with high precision. Calibration verifies accuracy using calibrated setting rings or gage blocks with a bore gage setting fixture. Accurate bore measurement is critical for engine cylinder, bearing housing, and hydraulic component manufacturing.
Inspect the bore gage for worn or damaged contact points, bent transfer rods, and proper indicator function. Verify the measuring range is appropriate for the bore to be measured. Check that the centralizing mechanism operates smoothly.
Using a calibrated setting ring at the nominal bore size, insert the bore gage and rock it to find the minimum reading (true diameter). Set the indicator to zero or record the as-found reading.
Using setting rings or gage block fixtures at a minimum of five points across the measurement range, verify the bore gage reading at each size. Record the displayed value and the certified reference value at each point.
Insert the bore gage into a single setting ring ten times, recording each reading. Calculate the standard deviation to assess repeatability of the centralizing mechanism and contact points.
Inspect the contact points under magnification for wear flats or damage. Worn contact points cause systematic errors and poor repeatability. Replace contact points if wear is detected.
Record all as-found and as-left data, setting ring IDs and certified values, and measurement uncertainty. Issue the calibration certificate and apply the calibration label.
Error at any test point must not exceed ±0.005 mm (±0.0002 in) for standard bore gages, or per the manufacturer's specification. Repeatability (standard deviation of ten readings) must not exceed one-half the resolution.
12 months
You need calibrated setting rings at the nominal bore sizes the gage will measure. For a multi-range bore gage, setting rings at the minimum, midpoint, and maximum of each range are recommended. Setting rings must be traceable and within their calibration period.
A bore gage uses a self-centering mechanism with a dial or digital indicator for comparative measurement, while an inside micrometer reads directly. Bore gages generally provide better repeatability for production measurement because the centralizing mechanism reduces operator influence.
Contact points should be inspected at each calibration and replaced when visible wear flats appear. In high-production environments, contact points may need replacement every 3-6 months. Carbide contact points last significantly longer than steel.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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