Philippe,

I'm designing a machine which is similar to yours, although slightly larger capacity, and trying to use as many ideas discussed in this forum as possible.

I am working on the Z carriage design and, as you said earlier, trying to keep the moving and fixed plates as close as possible. I cannot see from your CAD drawings how you have managed to fit the ballscrew nut in between the plates. The nut is wider than the profile rail + bearing height - have you put packing under the bearings to increase the space? I can see that you have machined steps into the plates and a recess where the ballscrew nut is fixed.