Oh, and spindle run-out, I forgot that. Best I can make out from reading, the usual spindles have a mixed bag in terms of specs and it's probably just a case of cross my fingers and hope I don't get a Friday one...?

I've started designing anyway; when I get it to somewhere sensible I'll share for comment...

What are the merits for move the platform and fixing the gantry on the X, versus fixed platform and moving gantry? It strikes me the moving platform will be easier to design and construct but I'll have to accept a larger keep-clear space at the sides of the machine?