Gage blocks are the fundamental dimensional length standards used to calibrate nearly all other dimensional instruments. They are manufactured to extremely tight tolerances and are the backbone of dimensional traceability. Calibration of gage blocks is typically performed by comparison to a higher-grade master set using a gage block comparator or by interferometric methods.
Gage block calibration must be performed in a temperature-controlled environment at 20 °C ±0.5 °C. Allow the gage blocks and master set to thermally soak for a minimum of 24 hours. Record the ambient temperature and humidity.
Clean all gage blocks with a lint-free cloth and appropriate solvent. Inspect for burrs, scratches, corrosion, or surface damage under magnification. Check that blocks wring together properly — poor wringing indicates surface quality issues.
Using a gage block comparator, compare each block to the corresponding master block. Take a minimum of three readings for each block, zeroing on the master before each comparison. Record the deviation from the master value.
Add the measured deviation to the certified master block value to determine the actual size of each block under test. Calculate the measurement uncertainty for each block.
Compare the actual size deviations and flatness/parallelism data to the tolerance tables in ASME B89.1.9 or ISO 3650. Determine whether each block meets its designated grade (0, AS-1, AS-2, K, etc.).
Issue a calibration certificate listing the certified length, deviation from nominal, and uncertainty for each gage block. Include the master set ID, environmental conditions, and grade determination.
Per ASME B89.1.9 Grade AS-1 (equivalent to ISO Grade 0): length tolerance is ±(0.05 + 0.001L) µm where L is nominal length in mm. Grade AS-2 (ISO Grade 1): ±(0.10 + 0.002L) µm. Each block must meet its designated grade tolerance for length, flatness, and parallelism.
12 to 60 months depending on grade and usage
Master (reference) gage blocks used only for calibration may have intervals of 3-5 years. Working gage blocks used daily on the shop floor should be calibrated every 12 months. The interval depends on usage, storage conditions, and historical calibration data.
Calibrating gage blocks requires a master set of one grade higher, a precision comparator, and a controlled environment at 20 °C. Most users send gage blocks to an accredited (ISO 17025) calibration laboratory. Only primary metrology labs calibrate gage blocks by interferometry.
Common causes include surface wear from wringing and handling, corrosion from fingerprints or humidity, burrs from accidental contact with hard surfaces, and dimensional instability of the steel over time. Proper handling (clean hands or gloves, prompt de-wringing, and corrosion-inhibiting storage) extends gage block life.
CalibrationOS tracks due dates, stores certificates, and generates audit-ready reports.
Get Started Free