Hi spresv

Nice first machine, well done. I've sketched, deleted, pondered and wondered about doing an ATC spindle driven by my chinese spindle, along the lines you describe. Things I thought about:
Running the spindle upside down (Like Deans says) - but didn't think about turning it the other way for direct machining!

Limit to 12,000rpm to make the cassette bearing spec manageable (plus limit centrifugal forces in the the ATC mechanism)

Tormach TTS system based on R8 spindle (but hadn't seen the LMS one, was thinking of making my own before you pointed that one out, thanks)
In case you missed it they added the drawings - and they are metric:
Click image for larger version.  Name: 1407SpindleR8.pdf  Views: 414  Size: 8.1 KB  ID: 20137

Gear down with at least 1 pulley set, maybe 2, to get the speed way down whilst multiplying the torque (hadn't decided on lower speed but maybe to 2000rpm ?)

I also thought about the constant side loading but I was prepared to give it a try. Could rotate the spindle body around from time to time I suppose to load a different part of the outer race?

The main thing stopping me doing the detailed work was that I should really finish my current machine (which is direct drive) - . . . although designing it in now before making the Y and Z parts would be better than a retro fit . . . . hum . . .