Hi Thomas - Agree with Joe above. So if you are to laser cut everything and really want to overcast in EG, then laser cut and bend everything and bolt it together. Zero welds. Then overcast. The bolting allows adjustment, bolted joints are damp and then it all gets frozen in the cast. I have made 4 routers all laser cut with flanges and bolted together. System works very well. Make armature as light as possible. The bulk size of EG will be the stiffness. Revisit FE in F360 its worth the effort for the insight it gives. In your case model the steel and EG separate, load them the same to figure out the relative stiffness of the two. Then if your up for it you have to model the EG, boolean the armature so it becomes an exact hollow then add the armature back in and load it up. F360 may even do a modal analysis so you can pick up vibration modes (which will be zero in the casting being such a chunk, at least modes that are not of interest for a machine like this) There are heaps of successful 100% steel machines in the forum so rigidity trumps dampness and machine cannot be too stiff.

If your keen on EG you have to do some costing and tests because if you choose sand and epoxy you will not get past 25GPa stiffness and then you have to use heaps. Your in Europe so look up Rampf known product with known modulus very helpful....Peter