The CAD cleanup tolerance is used to determine if two surface edges are the same and if two surface vertices are the same.  There are two items controlled by this setting:

 

If you use the automatic setting, the complexity of the surface and edge geometries are taken into account and a tolerance is selected to maximize the number of shared edges.  To specify a manual cleanup tolerance value, it must be greater than the default value.  The readers only modify data if the data stays within the original data tolerance.

Increasing the tolerance may cause problems.  When this value is modified, any features equal to or less than the tolerance are eliminated.  The readers do not include any edge with a length less than the tolerance; if there are edges present that are important to the surface, that surface will be distorted, or will fail to trim properly.  Similarly, surfaces smaller than the tolerance may not be imported.

If the file you have read has many very short edges, it may be worthwhile to reread the file using a larger tolerance.  The same holds true if surfaces appear to be "inside out" when surface lines are displayed.

The tolerance value should not be set to a value greater than the node tol used for your element mesh, set in the Options panel.

 

See Also:

Geometry Terminology