Sketcher ConstrainDiameter

From FreeCAD Documentation

Sketcher ConstrainDiameter

Menu location
Sketch → Sketcher constraints → Constrain diameter
Default shortcut
Introduced in version
See also
Sketcher ConstrainRadiam, Sketcher ConstrainRadius


The Sketcher ConstrainDiameter tool fixes the diameter of circles and arcs. It cannot be used for B-spline weight circles.


See also: Drawing aids.

Continue mode

  1. Make sure there is no selection.
  2. There are several ways to invoke the tool:
    • introduced in version 1.0: If the Dimensioning constraints preference is set to Single tool (default): press the down arrow to the right of the button and select the Constrain diameter option from the dropdown.
    • If this preference has a different value (and in version 0.21 and below): press the Constrain diameter button.
    • Select the Sketch → Sketcher constraints → Constrain diameter option from the menu.
    • introduced in version 1.0: Right-click in the 3D view and select the Dimension → Constrain diameter option from the context menu.
    • Use the keyboard shortcut: K then O.
  3. The cursor changes to a cross with the tool icon.
  4. Select the edge of a circle or arc.
  5. If a driving dimensional constraint is created, depending on the preferences, a dialog opens to edit its value.
  6. A constraint is added.
  7. Optionally keep creating constraints.
  8. To finish, right-click or press Esc, or start another geometry or constraint creation tool.

Run-once mode

  1. Select the edge of one or more circles or arcs.
  2. Invoke the tool as explained above.
  3. Optionally edit the constraint value.
  4. Depending on the selection one or more constraints are added, see Notes.



Sketch.addConstraint(Sketcher.Constraint('Diameter', ArcOrCircle, App.Units.Quantity('123.0 mm')))

The Sketcher scripting page explains the values which can be used for ArcOrCircle, and contains further examples on how to create constraints from Python scripts.