How to Loft Between Multiple Sketches in FreeCAD

Creating a loft across multiple cross-sections in FreeCAD allows you to generate complex, organic, or transitioning 3D shapes that cannot be created using standard extrusions. This guide explains how to prepare your sketches properly, set up offset planes, and use the Additive Loft tool in the Part Design workbench to connect multiple cross-sections into a single solid feature.

Step 1: Create the Offset Datum Planes

To loft across multiple cross-sections, each sketch must reside on its own plane along your desired path.

  1. Open FreeCAD, create a new document, and switch to the Part Design workbench.
  2. Create an Active Body.
  3. Create a Datum Plane by clicking the Datum Plane tool. Under the combo view, set its attachment mode to an existing plane (such as the XY_Plane) and adjust the Z offset in the Attachment properties to specify its height.
  4. Repeat this step for as many cross-sections as you need, offsetting each datum plane further along the axis.

Step 2: Draw Your Cross-Section Sketches

  1. Select the base plane (or base Datum Plane) and click Create Sketch.
  2. Draw your first closed profile (e.g., a circle or rectangle), fully constrain it, and close the sketch.
  3. Select your second Datum Plane, create a new sketch, draw the second profile, and close it.
  4. Repeat this for all remaining planes. Note: Ensure all sketches are either strictly closed profiles for a solid or open wires for a surface. Mixing open and closed sketches will cause the operation to fail.

Step 3: Execute the Additive Loft

  1. Select the first sketch in the tree view (the base of the loft).
  2. Click the Additive Loft icon in the Part Design toolbar.
  3. In the Tasks panel on the left, click the Add Section button.
  4. In the 3D viewport, click on the edge or face of the second sketch. FreeCAD will draw a preview connecting the first two sketches.
  5. Click Add Section again and click on the third sketch. Continue this process sequentially until all profiles are selected.
  6. Choose your loft settings in the Tasks panel:
    • Ruled Surface: Check this if you want flat, faceted transitions between sketches instead of smooth, curved transitions.
    • Closed: Check this if you want the start and end sketches to loop back together into a closed ring.
  7. Click OK to generate the solid feature.

Troubleshooting Common Loft Issues

  • Twisted Geometry: If the generated shape appears twisted, the start points (first vertex) of your sketches do not align. Reorient your sketches or align the initial vertices to prevent the loft from crossing over itself.
  • Self-Intersection Errors: If cross-sections change radically in size over short distances, geometry may intersect itself. Increase the distance between sketches or add intermediate transition sketches to guide the geometry smoothly.