The RCAT 0030 is very solid when it comes to the base. The base is quite rigid in all degrees of freedom, however, it is easy to see its weak point in restrospect: the attachment from the x carraige to the bed. There is a diving board effect that happens at the edges and it could lead to major deflections. Thus the search for a more rigid structure is here.
# Side face attachments
The vertical side face needs to attach to the horizontal side face at some point. There is a desire to maintain the base as close to the 0030 as possible. So for the 0040, the edge rail webs will be swapped out to fit a more boxy way to attach rails for the bearings.