The explosion of new computer tools for anyone with a desire to work in mechanical design and manufacturing is impressive, and here is an opportunity to try out a real heavyweight from Autodesk. You can download Autodesk Inventor Fusion, which is offered as a technical preview, and use it free of charge until it expires, but that's quite a long time down the road, January 1st, 2013 on the Mac and April 1st, 2013 for the Windows version.
Inventor Fusion derives its name from the fact that it is the first 3-D modeling package that allows users to switch between solid and surface modeling. This app enables robust mechanical engineering and spontaneous artistic expression with the same tools. It can natively export .STL files, the key file type needed to 3-D print or mill objects. It can import DWG files, making it easy to design things in Adobe Illustrator or similar vector-based programs and turn them into three-dimensional objects. There are very few things a hobbyist will need to do that this software can’t support.
Learn it, use it, put it through its paces and see if it's right for you. If you've never used CAD software like this before, here's your chance to see if you can master it, certainly no small task, but there are plenty of tutorials and online help to guide you through the process.
Opportunities like this to learn skills that are substantial and valuable are all around us, it continually amazes me and the only thing stopping anyone is desire and hard work. Nice!