You are stuck with it. The MiniMills both standard and Super are lightweight machines and they flex when the table accelerates; the head 'nods'. Slow the feed down and the 'swirls' are not as noticeable but they do not go away unless you go painfully slow. It is more noticeable on the Super MiniMills and I think that is because they have faster servos and higher acceleration.
I have contemplated a couple of experiments to try and reduce the 'nodding'. One is to fill the column of the machine with concrete, actually not filled directly, first I would insert a rubber bladder so there would be a resilient layer between the concrete and the casting. The problem with doing this experiment is that there are cables that would have to be rerouted and if it didn't help reduce the swirls, or if the weight of the concrete distorted the machine, it would be impossible to remove the concrete.
The other ideais to try a scaled down version of what is done on some tall buildings in high earthquake risk areas. Really heavy weights are fastened to the top of the structure on resilient mounts. The vibration frequency of these weights on their mounts is very different to the natural vibration frequency of the building and the two different frequencies interfere and reduce the sway of the building in an earthquake. Possibly some day I will try this, I have looked and I think I could figure out a way of fastening a few hundred pounds of something at the top of the column.
An open mind is a virtue...so long as all the common sense has not leaked out.