Thanks for that, and I was certainly aware that I was jumping-in at the deep end with this concept and had already thought of buying a fairly simple machine to start with just for learning - one of the attractions of my design I think though is that it could/would be operated purely as a 3-axis machine most of the time anyway, so hopefully could itself act as stepping-stone in the learning process. In fact, with a bit of fore-thought, the entire machine could be initially built only as a 3-axis but constructed in a way that allowed the 4th and 5th axis capability to be added at a later date

Thanks again for your comments!