There's an absolutely fantastic open source 3D CAD program called SolveSpace (http://solvespace.com/index.pl http://solvespace.com/index.pl) For some reason it

There's an absolutely fantastic open source 3D CAD program called SolveSpace (http://solvespace.com/index.pl http://solvespace.com/index.pl) For some reason it's barely known about, which is a shame. It's truly fantastic - once you understand the UI it's almost as powerful as SolidWorks or other commercial parametric CAD systems (for smaller tasks anyway - once you get larger and more complex models it starts to struggle).