Playing with Tinkercad, a website for creating 3D models with a simple interface.It has a couple of fun things: it's easy to create objects combining primitive shapes in an ajax/html5 canvas app. The shapes can be sent to several 3D printing shops or (my favorite) downloaded as an STL file to the local computer.
Tinkercad interface: click on a primitive, position, resize, rotate on the space. Some operations display measurements in milimeters in real time.
In Tinkercad the STL file can be downloaded. Here it is, opened in Meshlab. A promising site. The tip came from Popular Mechanics: How to Get Started: 3D Modeling and Printing.