How to Create a Datum Point in FreeCAD

This guide explains how to create and position a Datum Point using the Part Design workbench in FreeCAD. You will learn the exact steps to generate a reference point, bind it to existing 3D geometry using attachment modes, and use it as a robust, parametric anchor for positioning downstream features like holes, sketches, and datum planes.

What is a Datum Point?

A Datum Point is an auxiliary parametric feature available in FreeCAD’s Part Design workbench. Unlike standard sketch vertices, a Datum Point exists in 3D space independently of a single sketch plane. It serves as an accurate reference for placing other modeling elements, ensuring that changes to base geometry automatically update the location of dependent features without breaking the model.

Steps to Create and Position a Datum Point

1. Activate the Part Design Workbench and Target Body

  1. Switch to the Part Design workbench from the workbench dropdown menu.
  2. Ensure the active Body contains your existing geometry, or create a new Body. A body must be active (indicated by bold text in the Model tree) to contain datum entities.

2. Insert the Datum Point

  1. In the Part Design toolbar, locate and click the Create a datum point button (the icon resembles a yellow point with coordinate indicators).
  2. The Datum point parameters panel will appear in the Tasks tab on the left, displaying attachment options.

3. Select Reference Geometry (Attachment)

To position the Datum Point parametrically, you must attach it to existing geometric references:

  1. In the 3D view, select the reference geometry you want the point bound to. References can include vertices, edges, circular centers, or planar faces.
  2. In the Attachment panel, click Reference 1 if your selection was not automatically captured. You can add up to four references depending on the required calculation.
  3. FreeCAD will automatically suggest the best Attachment Mode (such as Center of curvature, Object's X Y Z, or Intersection). You can manually select a different mode from the list if the default does not match your intent.

4. Fine-Tune Placement Using Offsets

If the point needs to sit at a specific offset from the reference geometry:

  1. Go to the Attachment Offset section in the Tasks panel.
  2. Enter values into the X, Y, or Z offset fields to shift the point along the local coordinate system of the attachment reference.
  3. You can also adjust angular rotations if using an orientation-dependent attachment mode.
  4. Click OK to generate the Datum Point. It will now appear in your tree view as DatumPoint.

Using the Datum Point to Position Features

Once your Datum Point is created, you can use it to drive other modeling operations:

  • Positioning a Sketch: Select the Datum Point first, then click Create a new sketch. The sketch plane origin will bind directly to the Datum Point.
  • Placing a Hole: Select the Datum Point and click the Hole tool. FreeCAD can use the point to define the hole’s center axis normal to a chosen reference surface.
  • Creating a Datum Line or Plane: Select the Datum Point alongside another vertex, line, or face to generate angled datum axes or construction planes for complex angled cuts.