Ring gages are fixed-limit gages used to verify the external diameter of cylindrical parts. Go and No-Go ring gages provide pass/fail inspection against dimensional tolerances. Calibration measures the actual bore diameter of the ring gage and compares it to the nominal and tolerance limits.
Inspect the ring gage for wear, burrs, scratches, or corrosion on the bore surface. Check that the gage is properly identified with nominal size, tolerance class, and Go/No-Go designation. Clean thoroughly before measurement.
Allow the ring gage and reference standards to stabilize at 20 °C (68 °F) for a minimum of 4 hours, or until thermal equilibrium is achieved. Record the ambient temperature during measurement.
Measure the bore diameter at a minimum of two planes (near each face) and two orientations (0° and 90°) in each plane, giving four measurements. Use an internal micrometer, bore gauge calibrated with gage blocks, or CMM with calibrated stylus.
Evaluate the out-of-roundness from the diameter measurements at each plane. The difference between maximum and minimum diameters at a given plane indicates the roundness deviation.
Compare current measurements to previous calibration data to assess the rate of wear. If the ring gage is approaching its wear limit, note this on the calibration certificate.
Record all measurements with uncertainty. Determine if the ring gage is within its tolerance class. Issue the calibration certificate. If the gage is out of tolerance due to wear, condemn it and remove from service.
The measured bore diameter must be within the tolerance limits for the applicable gage class per ASME B89.1.6. For a Class XX Go ring gage, the bore tolerance is typically +0.00005 in (+1.27 µm) from nominal. Roundness deviation must not exceed one-half the size tolerance.
12 months, or based on usage frequency
A ring gage is worn out when the bore diameter exceeds the wear limit for its tolerance class. Tracking calibration data over time reveals the wear trend. When the gage is near its wear limit, it should be replaced before the next calibration interval.
A Go ring gage must fit over the part (verifying the part is not too large). A No-Go ring gage must not fit over the part (verifying the part is not too small). Together, they verify the part diameter is within the specified tolerance band.
In some cases, ring gages can be re-lapped to restore the bore diameter to nominal, but only if sufficient material remains. The gage blank must be evaluated by a qualified gage manufacturer to determine if reconditioning is feasible.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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