You can edit any numerical parameters that define a datum; for example, the X-, Y-, and Z-coordinates used to define a datum point. However, a datum is always defined by the same underlying geometry you selected when you created it; if you need to define the datum using different geometry, you must delete the datum and create a new one. You can create a datum on a part in the Part or Property module or on an assembly in other modules. If you create a dependent datum on a part, the datum moves along with an instance of the part in the Assembly module. If you create a dependent datum on the assembly by selecting entities from a part instance, the datum moves along with the instance in the Assembly module. However, if you create a datum on the assembly by entering coordinates in the prompt area, the datum remains fixed when the instance moves. When you modify a feature, you should be aware of any parent-child relationships between your dependent datum and the modified feature. For example, consider Figure 1, which shows a dependent datum axis passing through the midpoint of two arcs. The midpoints of the arcs that define the location of the datum axis are parents of the datum axis. ![]() If you modify the part, Abaqus/CAE regenerates the datum axis so that it still passes through the two midpoints, as shown in Figure 2. ![]() |