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Where to Put Datums?

Maya Lin-Takahashi • • 6 min read
Where to Put Datums?

On a surface
The symbol must be placed on or with one single extension line out of the datum surface. This means that the datum is only on the surface of the part where it is shown. If it is on one side of a rectangular object like a box, the datum surface is only the side where the symbol is shown.

Do datums need to be perpendicular?

The standard defines a datum as a theoretically exact point, axis, or plane. ... It may require using datum targets, but a theoretical plane can still be constructed from those targets. So again, it's true that the theoretical datums mentioned in a feature control frame are perpendicular to each other.

Does order of datums matter?

Datums are specified in order of precedence as they appear from left to right in the feature control frame; they need not be in alphabetical order. Datum A is the primary datum, datum B is the secondary datum, and datum C is the tertiary datum because this is the order in which they appear in the feature control frame.

Maya Lin-Takahashi
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Maya Lin-Takahashi

Maya is a hardware enthusiast who tests and reviews smart home devices, smartphones, wearables, and audio gear. She focuses on practical consumer value and build quality.