What are you looking at machining? Looking at your design either supported round rail or the profiled rail would do.
I think the 20mm profiled rail is a bit of an overkill for hte size of you machine? and 15mm would be fine.
With the round rail you can also use the SHF mountings for supporting the rail and this will connect direct to the aluminium profiles with t slots.

Gary

Quote Originally Posted by lateAtNight View Post
Its just after Kieth saying in effect saying my first design was crap, I went back to the drawing board. It got slightly better, but now for a third time (and hopefully final time) I re-designed, to... (see pic). Which uses linear rails.

I'd rather have linear rails because the attach easily to aluminium profile, where as supported rail, i would need to do lots of drilling etc. So what I was basically asking was, can I get away with using the rail, or is round supported better?