I'm only talking about one surface with precision in a base mold and two surfaces with precision in the column mold, why do more work than necessary.On the precision mold topic.
Sure, making a very precise mold would be nice. The problem with it is that its difficult, slow and expensive. And only a few surfaces need precision anyway. A simpler way of making precise bases used in industry is replication. They basically cast the base with a cheap, imprecise mold and then add precision to the few surfaces where it's needed: to bolt linear rails for example. But they do not do that by grinding the granite the way I do it here but by molding another layer of epoxy to the base in a precise way (Note though, that grinding of EG bases after casting was used in industry in the 60s and 70s). The way they create precision is by applying a thin layer of epoxy-based paste (e.g. moglice) to the place where precision is needed and then lowering a straight edge or surface plate on top of it in a very precise way. Injecting liquid filler between the rough base and the precise surface is another way. After curing the reference plate/edge is removed revealing a precise surface behind (this is why its called replication). Cincinnati Milacron used this technique on some of their their grinders for example. Of course this still requires a precise reference surface, which is expensive but at least you need a smaller one than a whole mold. In any case for this build I will stick with grinding rather than switch to the replication method because I know how to do it now, it seems to work and I only need to grind a few surfaces.