What are Datum Targets in GD&T
Mufaddal Rasheed 
How to interpret Datum targets? what do they mean and why are they used on a GD&T drawing?
What are datum targets?
Geometric targets on the drawing which indicate the touch points , lines or areas of the datums .
General annotation:
Why are they used?
- Irregular and large part– Establishing datum on irregular surface can be ambiguous for inspection , hence specifying the areas, lines or points which have to be used as part of a datum scheme are important. Generally these datum targets are in planar surfaces of the part which makes them easier to hold and inspect
- Parts with Welds,
- Cast and forged parts.
- Large sheet metal parts
- Multi planar parts which have multiple parallel planar surfaces at different levels
Basically , Where a single isolated datum surface may not suffice for stability and constraint of degrees of freedom for the part.
An example would be the door of a car which is a large sheet metal component. Requires datum targets to be established to establish datums.
3-2-1 principle for constraining 6 degrees of freedom
Here is a rectangular block , if we use 6 points then the position of block in space will be constrained.
Ideally you need 6 points to constrain 6 degrees of freedom.
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Categories: : GD & Tolerancing