TABLE OF CONTENTS Inspection of certain types of geometrical tolerances (e.g. coaxiality tolerance) is relatively costly. Often in such cases in the first step a "quick" (but less precise) inspection is chosen and only in case of doubt is the more precise (and more costly) inspection executed in a second step.
For example, in the cases of a coaxiality tolerance or a common straightness tolerance zone of axes, the inspection in the first step is performed as if there were a runout tolerance of the same value. Only when this tolerance is exceeded is it checked by a more precise method whether the coaxiality tolerance or the straightness tolerance of the axis is exceeded.
Similar considerations apply in the cases of a cylindricity tolerance and a roundness tolerance. In the first step the check of run-out may be executed.
Often with related geometrical tolerances, the precise verification of the minimum rock requirement is very costly. Therefore approximate inspection methods are used with the aid of V-blocks, mandrels, centre holes, etc. Using V-blocks, the form deviation of the datum feature leads to simulation of a larger related geometrical deviation than actually exists (according to the definition). Depending on the shape of the form deviation and the angle of the V-block, the increase can be equal or less than the form deviation of the datum feature (see 18.7.4.3).
A similar consideration applies with the use of centre holes. There the eccentricity of the centre hole relative to the datum feature increases...
