Introduction to 3D T&A
© 2022, ASCENT - Center for Technical Knowledge® 1–17
Figure 1–11
The next step is to define the semantic datums for the model.
They can be defined on planar faces or reference planes in the
model. If a non-planar surface is selected, datum target points
must be defined to establish the datum.
In CATIA, datum
reference frames are
also called datum
systems. The terms are
used interchangeably.
Datum reference frames (DRF) provide the basis for all
geometrical tolerancing in the model. The DRF's are developed
from a selection of semantic datums. Once created, DRF's are
added to the specification tree and the Semantic Tolerancing
Advisor dialog box.
Three semantic datums (A, B, and C) and a datum reference
frame (A|B|C) have been defined for the part model, as shown in
Figure 1–12.
Figure 1–12
Step 4 - Create datum reference frames.
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