Manufacturing engineers expect the high accuracy performance of a machining centre to yield highly accurate parts. But this is not necessarily the case. Part accuracy is affected by various errors, which may be broadly classified into geometric and processing errors. Geometric errors include positioning accuracy, roll, pitch, yaw, straightness and squareness. Processing errors include tooling, fixturing, NC programming, and thermal errors.
Thermal errors play a considerable role in part accuracy.
Keep in mind that inspection errors must also be considered. Thermal Expansion Many manufacturing plants require machining of materials as varied as titanium, cast iron, steel, brass, aluminium, and magnesium on a single machine. The standards organisations throughout the world have adopted 68F or 20C as the standard temperature for the measurement of length. This means that a specific length for all materials at the standard temperature of 68F or 20C will have the same exact length. At any other temperature, the length will vary according to the CTE of that material.