| The qualification of a
complete part coordinate system requires the coordinate system to be
unambiguously specified on the technical drawing. This part coordinate
system is also called datum, because it is the basis of the standard geometric elements to be checked.
In most cases, the coordinate system is formed by three
planes perpendicular to one another, as shown here.
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The three planes of
datum are usually designated A, B and C on the construction drawing.
- A: primary datum
- B: secondary datum
- C: tertiary datum
Attention: As can be seen from the example listed below,
the order of datums is of prime importance.
Note: However, the part coordinate
system must not always be formed by three planes, as shown by the following
digression:
Digression: Datum formed by cylinder and plane |
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