Thanks a lot. I could use a section of the G clamp rod as a tap. That's what I did with my allthread rod plastic nuts.

The 16mm belt I got, fits ok on the 16mm pulleys and there is a little side clearance...There will be some stretch in the belt but, I only intend to cut foam at first so It will be fine for me
Now that's good news and bad news. I would want to mill and route electric guitar bodies and neck, but i'm expecting a bit of sanding after machining anyway so a little chatter may be Ok. Or I might be wrong.