CAD Tolerances dialog box
The Edit | Graphic 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.
Angle Resolution tolerance - Determines the angle (in degrees) at which two angles are considered equal. It also determines if two vectors are considered equal by checking the angle between the two vectors.
Precision tolerance - Specifies the accuracy of iterated solutions on the geometry.
The Resolution, Angle 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, PC-DMIS identifies it as a circle, and any functions that depend on this information work 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, PC-DMIS considers the surfaces to be connected and there is not 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 uses that value instead of the default value.
CAD Angle Resolution Tolerance Information
The CAD angle resolution tolerance determines the angle (in degrees) at which two angles are considered equal. It also determines if two vectors are considered equal by checking the angle between the two vectors.
This tolerance is mainly used to check if geometry forms a feature when angles are involved. For example, a round slot has two circular arcs at its ends. The angle between the two circle normals must be within the angle resolution for the feature to be recognized as a round slot.
Another example is a square slot where adjacent sides must form 90 degree angles. If this angle is off more than the angle resolution, then the feature is not recognized as a square slot.
The default angle resolution tolerance is 0.5 degrees. The minimum angle resolution tolerance is 0.01 degrees and the maximum is 5.0 degrees. When you import a new CAD model, PC-DMIS sets the angle resolution tolerance to 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.