Create an Arc by Three Points in FreeCAD Sketcher

Creating an arc using three points in FreeCAD allows you to define a curved segment precisely by its endpoints and a point along its perimeter. This guide provides a straightforward walkthrough on selecting the correct tool in the Sketcher workbench, placing the three reference points in your active sketch, and applying standard geometric constraints to lock the arc into your design.

1. Open or Create a Sketch

  1. Launch FreeCAD and switch to the Sketcher Workbench (or Part Design Workbench).
  2. Create a new sketch on your desired plane (XY, XZ, or YZ) or double-click an existing sketch in the model tree to enter edit mode.

2. Activate the 3-Point Arc Tool

  1. Locate the Sketcher geometries toolbar.
  2. Click the dropdown arrow next to the Arc icon.
  3. Select Create an arc by 3 points (or use the top menu: Sketch → Sketcher geometries → Arc by 3 points). The cursor will change to crosshairs with an arc icon.

3. Place the Arc Points in the Viewport

The 3-point arc tool requires three sequential mouse clicks:

  1. First Click: Click in the 3D viewport to place the start point of the arc.
  2. Second Click: Move the cursor and click to set the endpoint of the arc.
  3. Third Click: Move the cursor perpendicular to the line between the first two points to adjust the curvature, then click to set a point along the circumference. This defines the radius and direction of the curve.

4. Apply Constraints

Once the arc is placed, it remains unconstrained:

  • Radius/Diameter: Select the arc rim and click the Constrain radius or Constrain diameter tool to lock its size.
  • Endpoints: Use the Constrain coincident tool to attach the endpoints to existing vertices, axes, or other geometry.
  • Tangent/Perpendicular: If connecting to lines or other curves, select the arc and the adjacent segment, then apply a Tangent constraint for smooth transitions.

Press Escape or right-click once to exit the arc creation tool.