scope:

Purpose and scope of application

This guideline applies to CMMs of any type and accuracy with mechanical or optical probing. Some manual CMMs are also suitable for acquiring the vast number of measuring points required for form measurement and can therefore not generally be excluded.

Limitations in the scope of application are a result of the CMMs capability to pick up an adequate number of points within an acceptable measuring time. For roundness measurement, the usual number of points per profile lies between 3600 and 4000. Not all CMMs permit the acquisition of so many points with an acceptable outlay. Form measurement on CMMs providing incomplete data acquisition is not covered by the scope of application of this guideline, as the comparability of results is not guaranteed in this case.

The VDI/VDE 2631 gives a detailed description of the measurement of roundness and straightness on form measuring instruments. Due to the focusing of this guideline and appropriate standards on such dedicated form measuring instruments, they can only be applied to a limited extent to form measurement using a CMM. Basically, only the principles can be used.

In addition to the measurement of roundness, cylindricity, straightness and flatness, CMMs are suitable for measuring line and surface form tolerances. This guideline therefore includes all form tolerances, but it is assumed that the principles of form measurement illustrated in VDI/VDE 2631 are known.

It is the purpose of this guideline to ensure the comparability of CMM form measurement results and their traceability. For this, no new definitions are created, but rules for form measurement on CMMs are established which take into account the special capabilities of coordinate measuring machines on the basis of existing form measurement standards. For better understanding of CMM properties, the machine design, the principle of form measurement and the effects which parameters have on the measuring deviations are described. Artefacts and procedures for acceptance testing and monitoring of CMMs used for form measurement are defined.