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Introduction

In FreeCAD the word "Datum" is normally used to refer to auxiliary geometry that is not part of the final Shape of the model, but used as a reference and support for sketches and other objects. Datums can be used in all workbenches. Some objects, such as a Std Part, a PartDesign Body and an Assembly, contain a coordinate system (Origin) by default.

The datums are derived from App GeoFeature:

• Part CoordinateSystem
• Part DatumPlane
• Part DatumLine
• Part DatumPoint

Usage

1. Switch to the PartDesign Workbench.
2. Press PartDesign Body.
3. Select the Origin of the Body, and make it visible by pressing the Space bar on your keyboard.
4. Press Part DatumPlane to open the Attachment task panel.
5. In the 3D View, click on one of the standard planes, for example, the XY-plane. Then press OK to close the task panel.
6. Now in the Tree View, select the newly created DatumPlane, and then press PartDesign NewSketch.
7. Create a closed wire, and then use PartDesign Pad to extrude the sketch, and create an initial solid.

Now you can move and rotate the DatumPlane as you wish, by changing its properties in the Property View, and the Sketch and Pad will follow its new Placement.

You can add other types of datums to be used with other sketches and features.