Hi Ard/Jon - The question of damping has always been a tough one due to the complexity of analysis and the conflicting data available. I ran the modal analysis on No23. The first mode is the column rocking at 203htz then it torques at 354htz then there's quite a few global modes. Since you mention the hollow the first local mode is the column walls panting at 800htz and 870htz. I'm thinking of making the column a bit asymmetric fwd and aft to counter this and provide a bit more stiffness. I have started to play with the base to reduce its mass but not successful with that yet. This is partially because I restrain it via the post which is a small object on a large base. I have to be careful not to optimise too hard here as in reality the "restraint" is a moving target depending on the part fixturing. Then there is the difference between dynamic stiffness and static stiffness and we'll only know that once its built! The static stiffness approach is sort of wrong in terms of what's happening when the machine is cutting as the tool and workpiece are intimately connected. In the static stiffness approach the tool and workpiece move apart which can't happen in practice... But its an easy and understood approach to getting a stiff machine... I will run a damping solver on this once the base is better resolved...Peter would be good to get videos up here. You need to pester admin to allow MP4 vids