Hi All - Its magic - I organised No5 and No6 into the same height and depth. I then made all parts steel to represent the max stiffness it could be. No5 weighs 1.26 tonne and No6 weighs 1.77 tonnes. I bonded these all together and pulled on the spindle with 1000N and ..... they both deflected 0.0079mm or in stiffness terms 126N/um which is fantastic but I can't get that. So Why is it so? I built No6 base from No5 base and the bottom and corner have the same geometry. Its this corner that is the dominant (and same) deflection... Now I have the machine nailed to the earth, so I may place it on a surface, add friction and create an internal load like the tool/part would have to confirm the machine deflection would be the same.... The struggle goes on. keep Making Peter