How to Make Construction Lines in FreeCAD

This guide explains how to convert standard geometry lines into construction lines within FreeCAD's Sketcher workbench. You will learn the purpose of construction geometry, the exact steps to toggle existing lines between regular and construction modes using tools and shortcuts, and how to draw construction lines directly from the start.

Understanding Construction Lines in FreeCAD

In FreeCAD, regular sketch geometry appears as white lines by default and defines the actual shape used to generate 3D features such as pads, pockets, and revolves. Construction geometry appears as blue lines. These lines serve purely as references for dimensions, alignment, and constraints, and the software completely ignores them when generating 3D solid geometry.

How to Convert an Existing Line to a Construction Line

Converting any existing sketch element into construction geometry requires only a few clicks:

  1. Open Your Sketch: Double-click your sketch in the tree view to enter the Sketcher workbench editing mode.
  2. Select the Geometry: Click on the line, circle, arc, or multiple elements you wish to convert. Selected elements will turn green.
  3. Toggle the Mode: Click the Toggle Construction Geometry button in the Sketcher toolbar. The icon features an icon switching between a red solid line and a blue dashed line.

Once clicked, the selected geometry will turn blue, confirming it is now a construction element.

Using Keyboard Shortcuts

You can also use FreeCAD's built-in keyboard shortcuts to speed up your workflow:

  • Select the geometry you want to change.
  • Press G followed by N on your keyboard (the default shortcut for toggling geometry mode in modern FreeCAD versions).

Converting Construction Lines Back to Normal Lines

If you need a construction line to form part of your actual 3D profile, you can easily reverse the process:

  1. Click the blue construction line to select it.
  2. Click the Toggle Construction Geometry button or press the shortcut key (G, then N).
  3. The line will turn white, returning it to standard geometry.

Drawing Construction Lines Directly

If you know in advance that you need reference geometry, you can switch FreeCAD into construction mode before drawing:

  1. Ensure no geometry is selected in your sketch.
  2. Click the Toggle Construction Geometry button in the toolbar.
  3. The toolbar icons for drawing shapes (lines, rectangles, circles) will change from their standard colors to blue.
  4. Draw your shapes as usual; they will automatically be created as blue construction elements.
  5. Click the toggle button again when you want to resume drawing standard 3D-bound geometry.