From FreeCAD Documentation
- A Gordon surface requires a network of lines or curves that create a support network for the surface.
- The surface will be "tented" between and over these lines.
- In the example above the blue lines (or ribs) represent the shape of the surface at different points along surface.
- These can be thought of as cross sections along the surface. Or, like supports that the surface will "tent" over.
- The yellow lines represent the extent and shape of the surface between the cross sections ("ribs") defined by the blue lines.
- These lines (blue & yellow) can be created in sketches.
- The sketches containing the blue ribs would typically have a placement offset.
- Each "rib" is in a separate sketch.
- The sketches containing the extent/shape (yellow) lines will typically reference external geometry from the "rib" sketches for accurate positioning.
- These need to be created before the next step.
- Switch to the Curves workbench (install from Addon Manager is necessary, if not previously installed)
- Now select all the lines of that will define the surface.
- The order of selection defines the stitching or tenting order.
- Use multi-select to select all lines defining the surface. (Left click while holding the Ctrl key.)
- Select the ribs first, in order. (In the example above, select the blue lines from left to right. or right to left.)
- Continue to hold the Ctrl key and select the extent lines. (Yellow lines in the example above.)
- To invoke the command, do one of the following:
- Press the button
- Use the Surfaces → Gordon surface