Hi John,

Usually up to 80 kg gantry is OK for typical stepper and drivers, above that may be entering servo territory (=money!).

See post #2 here:
http://www.mycncuk.com/threads/6457-...80kg#post48417

I'm intrigued how you ended up with the design in post #22. That thin wall, and very open box section looks like it will resonate in practice, and the intermediate extrusions (to space away for the ballscrew?) are going to flex locally. The ends look fairly tricky to build and maybe a bit complicated.