## Changing CAD Tolerances

CAD Tolerances dialog box

The Edit | Graphics Display Window | CAD Tolerances menu item displays the CAD Tolerances dialog box. This dialog box allows you to view and modify the following CAD tolerances that are stored in the .cad file:

- Resolution tolerance - Determines the distances at which two XYZ points are considered coincident.

- Precision tolerance - Specifies the accuracy of iterated solutions on the geometry.

The Resolution and Precision boxes allow you to view and modify these tolerances.

CAD Resolution Tolerance Information

The resolution tolerance is the distance at which two XYZ points are considered to be coincident.

This tolerance determines whether or not a freeform geometry defines an analytic shape. For example, a freeform curve, depending on the tolerance, may or may not be defined as a circle. If the curve defines a circle within the resolution tolerance, then it will be identified as a circle by PC-DMIS and functions that depend on this information will function properly. For example, the Single-Click Auto Feature functionality depends on this information.

In addition, this tolerance determines whether or not two adjacent geometries are connected. For example, if you have PC-DMIS perform a Section Cut scan operation on the CAD model, PC-DMIS compares the gap between adjacent surfaces against the resolution tolerance. If the gap is within this tolerance, then it considers the surfaces to be connected and there will not be a break in the section cut.

The default resolution tolerance is 0.01 mm. The minimum resolution tolerance is 0.0001 mm and the maximum is 2.0 mm. When you import a new CAD model, PC-DMIS sets the resolution tolerance to the default value, except in cases where the imported CAD file itself specifies a resolution tolerance. For example, if an imported IGES file specifies a resolution tolerance in the header, PC-DMIS will use that value instead of the default value.

CAD Precision Tolerance Information

The precision tolerance specifies the accuracy of iterated solutions on the geometry. For example, during some find nominals operations, an iteration process is used to compute the solution on the CAD geometry. Once the solution is within the precision tolerance of the actual solution, the iteration process stops.

The smaller the precision tolerance, the slower the algorithms that use this tolerance for computing a solution.

The default precision tolerance is 0.00001 mm and this is the recommended tolerance to use. The minimum precision tolerance is 0.0000000001 mm and the maximum is 0.001 mm. When you import a new CAD model, the precision tolerance is set to the default value.