[Pipik]

Hi Rupesh - I did a drawing earlier on the side of the column. A web on the side is stiffer then going from 16mm to 20mm flat plate. Peter

That will not help. Any "webing" on the column is nonsense. It just beatiful, nothing more.
At mill machine, you need mass, mass, and mass again. You need to consume vibration, and no "webing" ever eat that vibrations. That only do mass itself. Only choice you need to make is decision, how much mass you want to invest in you mill. Thats the point.
You are building hobby machine. So you will probably do not want a 1ton machine, but if you want to cut any harder material than polystyrene, you must invest some mass (= material) to consume vibrations. I also did this mistake like you are doing now, and I will never do that again. You will spent a hundreds hours to make it alive, probably a few thousands dollars, so you really do not want to watch (and hear) a router bit avoiding material because the weak portal, because you want to save a few tens of dollars on material.

Just be smart - if you are cutting aluminium, you make cuts 0,03mm each rotation (0,03 per teeth). So if you will push your spindle in any direction with app. 30-50kg force, than the construction must not to move more that 0,03mm. Thats your goal. And any webing will not help you with that.

Ok, you surely can make cuts with weak machine, but only with small diameter, thats mean you will probably not be able to cut through 10mm aluminium because of short small diameter bit. And speeds? Precision? You will need to make a several finishes to reach 0,05mm precision instead of just roughing, make one finish, and insert a bearing.

I can send you a drawings of my latest machine, its very simmilar to yours you want to build. There is no complicated parts, simple to build, like yours, but this machine have 0,012mm repeatable precision, cutting aluminium with 12mm bit like a butter. You can inspire with that. And not to make mistakes like I did at my first machine.