Dimensioning Symmetry

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ID Feature Search ID Feature List box Last Two button Clear button Tolerance for Symmetry Dimensions Output To area Display check box Edit button Create button Close button Units area Analysis area

Dimension Symmetry dialog box

The Insert | Dimension | Symmetry menu option calculates the symmetry of a set of points with a datum feature, or two opposing lines with a datum feature.

According to the geometric dimensioning and tolerancing standard, the following graphic indicates how a symmetry dimension is displayed and interpreted.

Symmetry Dimension

Symmetry Dimension - Interpretation

1 - The center plane of datum feature A.

2 - Order of point measurements.

3 - 0.8 wide tolerance zone.

4 - Opposed elements, with alternating points.

5 - Derived median points.

Explanation of Previous Graphic

Within the limits of size and RFS, all median points of opposed elements of the slot must lie between two parallel planes 0.8 apart, the two planes being equally disposed about datum plane A. The specified tolerance and the datum reference can only apply on an RFS basis.

Because of the way the symmetry is defined, PC-DMIS limits the features that can be used for the symmetry dimension. Since the points must be equally arranged about the datum in order to find midpoints between them, you must either select a feature set with alternating points or two opposing lines with the same number of points.

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To Dimension a Feature Using the SYMMETRY Option:

Plus Tolerance for Symmetry