I didn't mean to offend you Rick,
just wanted to clarify that I already know the disadvantage of the machine being larger for the same workspace, i just didnt mention it in my first post, as it seems kind of obvious to me, sorry for the misunderstand regarding machine size, i should have said i would use 600mm rails if the gantry moves.

Could you tell me what experience you have made with the two methods please, thats whats most interesting for me.
Is the advantage of building a fixed gantry big enough to justify a larger machine foot print ?