During the past 30 years I’ve had the opportunity to measure quite a few manufactured parts, machine tools, fabrications, and large vessels. I’ve also reviewed hundreds of metrology surveys done by technicians. Unfortunately, on more than one occasion I’ve seen data that were scaled incorrectly or not scaled at all. The results of incorrect thermal scaling may cause inaccurate data, showing faulty parts even if the parts are not faulty. It is essential to understand the purpose and importance of thermal scaling.

Unless otherwise noted, a drawing or model is scaled at 1, or 68°F. In quality labs, temperatures are consistent even though that may not always be the case. Measuring different parts in varying temperatures may cause the material to expand and contract due to thermal change. This change can be calculated by using the coefficient of thermal expansion (CTE). Most measurement software packages include the capability to apply the CTE calculation to the measurement file based on a particular material type.

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