First prototype, spring 2013
On one hand, it was promising. It showed the feasibility of the build and proved, that the desired accuracy would be possible to achieve. On the other hand, it was about impossible to calibrate, certainly much more difficult than I could assume an average builder could do. And since the aim has been from the beginning to share the machine, this wasn't good. Further, slightest miss-alignment resulted stress to the bearings. In fact, the prototype died before I could get very much done on the software side. Back to the CAD.
Second prototype, autumn 2013
Much better, and actually works (or at least did work before I took it down, see later). I hadn't thought some details through and it showed. Also, a couple of non-fatal design mistakes needed some improvisation. Overall, I was happy about it, although a third design round was needed. The photo with the green carpet shows the second prototype detached from its table.
Software, winter 2013-2014
I'm using Visual C#, the most productive language I'm fluent with. After a false start with OpenCV (nothing wrong with that, it was mostly me) I got most of it done, using Aforge.NET vision library. In its current state, the software can kind of build boards, but I'm not happy with the overall workflow. Also, as I was adding stuff to the user interface as I went along, some parts that should be together are scattered around; time for some refactoring and finishing up. But some details about final calibration needed the (hopefully) final prototype build.
Third prototype, spring 2014
Building the third prototype took more time than I wanted to, mainly because I'm planning to offer a build it yourself kit once the project is finished. Arranging the storage of the parts, acquiring all of them and in some cases, waiting for a few months(!) of lead time was kind of frustrating. On the other hand, the time allowed me to finish off some audio projects, freeing time for finishing this project after the summer. Eventually, the third prototype got done, too. All looks good.