Hi Paul - When building a machine you need to summaries your resources and needs. contract machining, heat treat, painting, welding, comfort level with various technologies, etc etc including $$$$. Then find the pathway thru that puzzle that realises the machine you want. There are still hurdles with a cold cast machine.eg how do I deal with inserts and flatness etc. mainly to do with how accurate does this machine have to be? If your aiming at +/-0.1mm then a plywood machine or sheet metal machine or extruded aluminium machine is totally doable./ If your aiming at +/-0.01mm then you have to step up in quality of parts, machine all the important bits on a big VMC or manual mill. I think a grout cast machine base is a great thing, Plus I'd cast the saddle and the gantry... Consolidate as many parts as possible into one.
Machine rigidity is a big topic - If you have access to FE on your CAD its very helpful.. You describe the machine as a router but do you want to cut aluminium? as this lifts the bar quite high. By the way grout has the same COE as steel so it will expand and contract like steel. So do you have an exemplar machine in mind? This helps as then your not starting from scratch, they have been thru the movie a few times so have sorted some basic issues. Keep at it. I think its time you got some CAD models rolling what CAD do you use? or no CAD? Peter