Dimensional equipment is used in nearly every manufacturing environment and their measurements play an important role in monitoring any deviations within the manufacturing processes and to ensure the proper assembly and interchangeability of components.

The quality or calibration laboratories that manage that equipment will have a system in place to routinely calibrate the equipment to ensure that it continues to meet the proper specifications and will provide the correct and accurate measurement results.

Gage Blocks are the master dimensional standard used in most calibration laboratories. Gage Blocks are sets of individual blocks where two opposing faces have been precisely ground flat and parallel so that the faces are an exact distance apart. Precision Gage Blocks can have a length accuracy as low as a few micro-inches. They are usually made of hardened steel, tungsten or chromium carbide or ceramic. The blocks are in various standard-length sizes and can be combined together to create any length combination within the range of the set.

Temperature Effects

Temperature is the largest factor to be considered when performing dimensional calibrations not only of the equipment or parts to be measured but also the temperature of the measuring equipment standards and the temperature of the calibration environment. The materials that the parts are made from and the materials in the measuring equipment will change dimensions based on the coefficient of thermal expansion of the material.

The coefficient of thermal expansion is expressed in terms of the amount of change, per degree change, per unit length. For materials made from steel, the coefficient of thermal expansion is approximately 6.5 x 10-6”/deg F. Thus, a 1-inch steel gage block will lengthen approximately 6.5 millionths of an inch for every 1°F temperature change above 68°F.

Due to this thermal expansion, dimensional measurements must be referenced to a defined temperature. ISO standard ISO 1 ‘Geometrical Product Specifications’ defines that standard reference temperature at 20 °C (68°F). When performing dimensional calibrations, the measurements will need to be referenced back to this temperature.

This is usually accomplished by making all measurements in a 20°C temperature-controlled room or by making temperature corrections if the measurements are taken at a different temperature. If the materials of the equipment being calibrated and the reference standard are the same, then corrections are usually not required if the items are at the same temperature during calibration as the thermal expansion will affect the items the same.