[Mogilogi]

The concrete is not in the loadpath from tool to structure. The loadpath goes thru the steel bed to the bolts holding it to the frame which is all steel. Steel is 200GPa stiffness and concrete is 40GPa so the load travel's thru the stiffest medium which is the steel. So the concrete just adds weight.

Hi Peter langmuir design loadpath goes thru to steel bed to the almost 40 bolts acting as rebar then to concrete
So what is connecting the steel bed to the machine rails is the concrete as you see in the image, is this a good design ?



After the concrete there is a layer of epoxy to close all the tiny holes and prevent any liquid from effecting the concrete

Also why i need mass because the gantry and z can weight about 200kg depends on the design I will go with. So to have that much weight moving to stop it need heavy base so the machine don't fly off the ground.