Depth gages measure the depth of holes, slots, steps, and recesses from a reference surface. They range from simple depth micrometers to digital depth gages. Calibration verifies the accuracy of the depth measurement using gage blocks and a reference surface. Depth measurements are critical for counterbore, groove, and step dimensions.
Inspect the depth gage for damage to the base, rod, and measuring tip. Verify the display or dial functions correctly. Check that the base is flat and the rod slides freely without excessive play.
Place the depth gage on a clean, flat surface plate and verify the reading is zero (or record the as-found zero offset). The base must seat fully on the surface with the measuring rod retracted.
Create step heights using gage blocks on a surface plate. Test at a minimum of five points across the depth gage range. Place the gage base on the upper surface and lower the rod to contact the step surface. Record the reading and the known step height at each point.
Measure the same step height ten times, lifting the gage between measurements. Calculate the standard deviation to assess repeatability.
Check the flatness of the gage base by placing it on an optical flat or by measuring the gap at multiple positions on a surface plate. A worn or warped base will cause systematic errors.
Record all as-found data, errors at each test point, repeatability results, and base flatness findings. Issue the calibration certificate and apply the calibration label.
Error at any test point must not exceed ±0.02 mm (±0.001 in) for standard depth gages, or per the manufacturer's specification. Repeatability must not exceed one-half the resolution. Base flatness must not exceed 0.01 mm (0.0004 in).
12 months
Wring a gage block to the surface plate to create a step. The depth gage base sits on the gage block (upper surface) and the rod extends down to the surface plate. The known depth equals the gage block height. Use different block heights to create test points across the range.
A depth gage typically uses a plunger or digital indicator mechanism and reads directly. A depth micrometer uses a micrometer head for higher precision and includes interchangeable rods for different depth ranges. Both are calibrated using similar methods with gage blocks.
The base is the reference surface from which all measurements are made. If the base is worn, warped, or nicked, it will rock on the workpiece surface and introduce error in every measurement. Base flatness should be checked at each calibration.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
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