Quote Originally Posted by F.O.X View Post
I'm thinking of ACME (multi-start) instead of ball screw and aluminium (tube) for frame
Why aluminium tube? Surely steel is easier to join (by welding) and stronger for the money...

Quote Originally Posted by F.O.X View Post
3-axis upgradeable to removable 4th-axis (rotary)
I'll order the steppers kit soon
this is the link
http://cgi.ebay.com/4-Axis-Nema-23-S...item4155c86bd7
I think you'll find that kit to be of limited value. The stepper motors have an extremely high inductance (18mH), which combined with the low voltage that driver runs on will really limit your motor speed.