GD&T what is Datum feature?
Mufaddal Rasheed 
What is a Datum feature in GD&T and what does it mean in inspection in manufacturing?
Consider the drawing of a block
Isometric view:
Front view :
The annotation means that the bottom surface is the datum feature A primary datum .
When the actual manufactured part as per the drawing is inspected
The part (as manufactured) is placed on top of a gauge block in blue .
The gauge block is very precise in its form (fine gauge tolerance) as compared to the component being inspected .
Important observations:
- Datum feature is the tangible surface on the component or part
- Datum feature simulator is a gauge or surface plate which simulates the datum.
- Datum is the purely theoretical plane formed by the datum feature simulator
The top surface of the surface plate (blue) may not always match the bottom surface of the part. That is the difference between datum feature simulator and datum feature.
An example with all three datums applied on three mutually perpendicular features.
Datum planes formed by datum features for this drawing are shown. They together form the datum reference frame.
Learn more about how to Interpret GD&T callouts from this Free e-book on GD&T interpretations
To learn more about GD&T have a look at this course
Geometric Dimensioning and Tolerancing: Basics
Explore more topics in GD&T :
What is virtual condition in GD&T
Factors in Specifying tolerance
GD&T Regardless of feature size
GD&T maximum material condition
What is datum feature modifier
What is actual mating envelope
What is 3-2-1 principle in tolerancing
Applying GD&T scheme to a bracket
GD&T applied to patterns of features
Tolerance stack up analysis of a simple part
What are material conditions in GD&T
Composite position tolerance in GD&T
What are datum targets in GD&T
Verification of manufactured GD&T drawing
What are simultaneous requirements in GD&T
Calculating the geometric tolerance of a part
Developing GD&T scheme for a part
Traditional tolerancing vs GD&T
Categories: : GD & Tolerancing