For those who work on Mac, I have found a very powerfull 2D/3D program : Turbo3d . Visit the download page Dont worry if it is a french page, the software perfectly works in English. If you work on an Intel mac , download the Universal version. The other version if dedicated to G5 machines. The program imports a lot of 3D formats ( OBJ included) and has an STL export for stereolithography. This is what we need , isnt'it ?