Dec 3, 2011

Playing with FreeCAD: Trapezoids and Ribs

FreeCAD is an application  whose development I have been watching closely since I first learned about it. What I like on FreeCAD?
  • It is Free and Open Source Software.
  • It's a feature-based parametric solid modeler. I actually believe that this kind of modeling is the best way to create complex 3D entities.
  • FreeCAD has its own workflow without trying to mimic the way that other similar applications work.
FreeCAD is under active development and currently is on Alpha stage(FreeCAD's development team decided recently to remove the "Alpha" status from FreeCAD).
But despite the missing features it can create complex geometry thanks to its Sketcher which is a very good tool.
For example similar proprietary applications have automatic tools for the creation of trapezoids (Loft command) or ribs. These entities are very common on mechanical design. FreeCAD doesn't have these tools yet but it is very easy to create trapezoids and ribs in FreeCAD with the help of Sketcher. I have actually found 2 ways to do that.

The first way is to create 2D trabezoid and rib shapes with Sketcher an then use the Pad tool to make them 3D. By this way you may find helpful the creation of custom planes. It's very easy to create custom planes in FreeCAD with the primitives dialog box under the Part module.

 A 2D trapezoid shape created with Sketcher

A 2d rib created with Sketcher on a custom plane

 The final 3D shape. The Pad tool was used to create 3D geometry from the 2D sketches

The other way is the combination of 2D sketches and the Pocket tool. All you have to do is to cut properly 3D rectangles in order to create trapezoids and ribs.

Create 2 triangles with Sketcher on a 3D rectangular shape. 
After using the Pocket tool the result will be a trapezoid.

 In order to create a rib, just draw a triangle on a 3D rectangular shape and use the Pocket tool.

 The final result.

FreeCAD has all the necessary tools that you need to place correctly the 2D sketches on the 3D entities.


  1. Hi,

    Just so you know, this week in the FreeCAD forum after a short discussion is was decided to remove that "alpha" status. I mean, usually "alpha" will indicate software at a very early stage of development and prone to crashes. It's been a long time now that FreeCAD has move on from this phase.

  2. Thanks a lot! I made the necessary changes.