I have thought about the possibility of adding a 4th axis. Originally I was going to shorten the bed to allow the 4th axis to go across the front of the machine outside of the main bed and have an extension bed when not in use. I was not sure if the smaller frame would make for a less rigid structure. So I am currently thinking of having a removable single bed. This could then allow me to mount the 4th axis within the main frame. As home user I don't think that swapping the bed for 4th axis is too much of an issue for me - assuming I ever get to need/use the 4th axis.