This is just a short list of free ones. Each has its pros and cons, and each has a different approach to creation. There are a few more that I didn't list because I can't quite remember their names right now.
I could actually go in depth about the style differences in each one and who would prefer to use them. In one of my past lives I tought 3d modeling and animation.
I just had my first 3D model printed. It went very well. I found a free 3D CAD package I love, OpenSCAD.
It is not what you are probably expecting. It has no point and click interface to draw models. What it does offer is a consice language to describe your model in code. You develop and modify the model with a text editor. It also has a 3D model viewer so you can see the results and spin it around to your heart's content.
If you code the model properly you can use variables and change a dimension of many features by changing a single value.
With 100 lines of code my model was ready. No fussing with a mouse to line everything up. It generates STL for the printer.
It's definately not for everyone, but if you're a code / script developer it's very natural. I think it is much like coding VHDL instead of drawing schematics.
While blender is free and impressive in its ability to pull off some of the same features as bigger software by bigger companies, it isn't great for designing for 3d printing. CAD software would be better for this.
You can do it in blender, but measurement of items after their initial construction is done by eye. This is less than optimal.
@aeroengineer: The book that you mentioned, is very similar to a set of books that I loved to check out from my high school library. They were called Ingenious Mechanisms for Designers and Inventors. I would spend hours going through those books.
It looks liek they have folks who love them and folks who hate them :-) Plus they are mega expensive ... but maybe after I've finished reading my "507 Mechanical Movements" I'll be earger to read more...
@aeroengineer: I think, though that Autodesk 123D will meet the immediate needs that you have. I found it rather intuitive for simple stuff, but I may not be a good benchmark for this.
This does look interesting -- I'm going to be busy for the next few days, so I'll wait to see if anyone else has any input here, then I'll decide which package to play with and download it and install it and start preparing for the arrival of my 3D printer (I smile whenever I say that :-)
Sorry, I did not post any links, I just has a small break between projects at work. I did see your blog post that you mentioned, and for what it is worth, I also agree with you that many have lost some of the basic skills. I am not sure, though, if it is that there are less people with those skills, or if it is just that there are more people that are button pushers, and hence by percentage there are fewer that have those skills compared to the whole.
I had the opportunity to get my start doing aircraft restoration when I was 12. This helped pay my way through engineering school. As of about 5 years ago, I branched out and started to learn electronics, so I commend you for branching out to the mechanical side of things. There are a lot of fun things that can be done. I might end up starting a personal blog, I am not sure, but these are some of the things that I want to write about. The integration of electronics with mechanical hardware. I think that most consider it a bit of voodoo magic, but in reality it is no more challenging than designing the electronics. The biggest issue with the mechanical side of things is that tooling for production is rather expensive. It is a whole different though process, and hence the greatness of the expansion of 3D printers.
I think, though that Autodesk 123D will meet the immediate needs that you have. I found it rather intuitive for simple stuff, but I may not be a good benchmark for this.