Well, the mill is already very heavy, heavier that the Tormach PCNC 1100, so it will have to stay the way it is.
I will probably still go with the hollow column but increase the wall size to 2.5". Hoses and cables can be passed through the middle.
My idea, and this will sound crazy, is to cast the head around the spindle, forever bonding the spindle in. This will have the greatest strength and vibration absorption. I don't think I will ever want to replace the spindle, at least not with the same one I have which I'm very unlikely to find another.
I seriously thought about making it from steel as well. The weight would be crazy though, so I opted instead for EG with a serious internal skeleton made out of steel.
Flipping the saddle is a no go. Every vertical machining center is designed this way for a very good reason. It provides the maximum support for the saddle at all positions, improving rigidity. In a reverse arrangement (like in a Bridgeport-type mill) when you move the table to one end its whole weight is creating a torsion momentum that acts on the rails/slides. This can lead to bending of the entire table severely limiting precision.
The table size is made only slightly larger than the travel of the machine on purpose. This is so I can use the machine itself to mill the top of the table flat and cut the T-slots into it. I do not want to use any tool (less a machine shop!) that I don't already have in my garage. I also like the idea of using the machine to build itself!
Yeah, its hard to design these ahead of time, too much crap to think about. There is plenty of space between components so hopefully switches, cables, oiling hoses, way covers could be installed in a decent way after the main structure it in place.
Yeah, this makes sense. Commercial castings vary greatly on what kind of bearing between the column and base they use. None has a single large contract plane because of two factors I think: 1. Hard to machine such a large surface to the tolerance needed for good contact and 2. The weight would be too large. What I should do though is to make the bottom part of the column beefier by lowering the recess between the two legs of the column.
I will use a motor with an off-center weight that will be bolted straight to the bottom of the mold.