How to Make Circles Concentric in FreeCAD Sketch

Making two circles concentric in FreeCAD means aligning their centers so they share the exact same midpoint. This article provides a straightforward guide on how to use FreeCAD's Sketcher constraints—specifically the Coincident constraint—to quickly lock two separate circles into a concentric layout.

Method 1: Using Center Points (Most Common)

1. Open your active sketch containing the two circles.
2. Click on the center point of the first circle. The point will turn green to indicate it is selected.
3. Hold the Ctrl key (or Cmd on macOS) and click on the center point of the second circle so that both center points are selected.
4. Apply the coincident constraint by clicking the Constrain coincident button in the Sketcher toolbar, or by pressing the shortcut key C.

Both circles will immediately share the same center point, making them concentric.

Method 2: Selecting the Circle Perimeters

In modern versions of FreeCAD, you do not need to click the tiny center points directly:

1. Click directly on the circumference line of the first circle.
2. Hold Ctrl (or Cmd) and click on the circumference line of the second circle.
3. Click the Constrain coincident tool from the toolbar (or press C).

FreeCAD automatically detects that you have selected two circular curves and applies a concentric constraint to their center points.

Tips for Managing Concentric Circles

• Setting Diameters: Once the circles are concentric, define their sizes by selecting each circle's perimeter and applying the Constrain diameter tool (Shift + D) or the Constrain radius tool (Shift + R).
• Fixing Position: To fully constrain the concentric circles in your sketch, constrain their shared center point to the sketch origin (or to other fixed geometry) using vertical and horizontal distance constraints.