How to Create a Slot in FreeCAD Sketcher

Creating a slot shape in FreeCAD is a fundamental task for designing mechanical parts such as bolt channels and adjustment tracks. This guide explains how to quickly generate and dimension a standard slot using the dedicated Slot tool in FreeCAD's Sketcher Workbench, as well as how to fully constrain the geometry for parametric design stability.

Step 1: Open the Sketcher Workbench

  1. Open your project in FreeCAD and switch to the Sketcher Workbench (or the Part Design Workbench if working within a Body).
  2. Create a new sketch on your desired plane (e.g., XY-Plane) or open an existing sketch.

Step 2: Select the Slot Tool

  1. Locate the Create a slot tool in the Sketcher geometry toolbar (icon resembles an elongated pill/slot). Alternatively, access it via the top menu: Sketch → Sketcher geometries → Create a slot.
  2. Click the tool to activate it.

Step 3: Draw the Slot

  1. Click in the 3D view to place the center point of the first semicircular end.
  2. Move your cursor and click to set the center point of the opposite semicircular end. This establishes the length and angle of the slot.
  3. Move your cursor away from the center line to define the radius (width) of the slot, then click a third time to finalize the basic shape.

Step 4: Apply Constraints

To prevent the shape from shifting unexpectedly, apply geometric and dimensional constraints:

  • Orientation: Select the center line between the arc centers and apply a Horizontal Constraint or Vertical Constraint to align the slot.
  • Length: Select the center line (or both arc centers) and apply a Distance Constraint to set the center-to-center length.
  • Width: Select one of the outer arcs and apply a Radius Constraint (or Diameter Constraint) to set the slot's width.
  • Position: Constrain one of the center points to the sketch origin or existing geometry using the Coincident Constraint or dimensional distance constraints until the sketch turns completely green (fully constrained).

Alternative: Manual Slot Creation

If you need an asymmetrical or specialized slot, you can construct one manually:

  1. Draw two parallel lines using the Line tool.
  2. Connect their open ends using the Arc by center, start, and end points tool or the 3-Point Arc tool.
  3. Apply Tangent Constraints between each arc end and its adjacent line.
  4. Ensure both arcs share an Equal Constraint for symmetry before dimensioning.