Initial Concepts

RHS Frame

This is the initial concept I designed. It involves some RHS and steel plates/bars that will be milled flat. 

I've also looked into fill the tubes with epoxy granite to increase mass and dampen vibrations.

Epoxy Granite Frame

This is a second version that would require casting with epoxy granite(E/G). Research shows that E/G has far better damping qualities than a steel frame; the mass is also a plus in keeping the machine rigid.