Has anyone explored the possibility of using their 4th axis as an indexable tool holder for turning operations? Or possibly for machining operations, using it as a carousel to hold TTS tools and in combination with a power drawbar? I haven't had the time to do any experimentation with it but thought I'd throw the (maybe not so original?) idea out there to see if anyone else has already headed down that route.
Interesting thought. I'm not sure about the indexable toolholder. How does it improve over clamping them in a rack on the table and using the x/y for positioning instead of the x/a. The tool changer idea is interesting, however it will take a lot of table space unless you hang it out over the side and then the weight might be a problem. An RT might be a good source of bits for a ligthened version. However it would be slow and you still need to move the x-axis to go and pick up the next tool. So again a simple tool rack on the end of the table, using the x/y, would possibly work just as well for less complication.
I think what you are proposing is to use the a-axis instead of the y-axis for tool positioning. I'm not sure I see a significant advantage unless you can use it to reduce the table space required by an x/y tool positioning system.
Not knocking the idea, just a few thoughts.