I realized my video showed the belts fluttering which is not really the issue. The head of the unit shakes. So tonight I did a large rectangle pattern to see if it just needed “breaking in”. I noticed that it got a lot worse at the edges. I stopped the pattern and noticed that the middle rails are not parallel to the side rails. Both x and y. I took all of the rail system apart and started from the beginning. The outside rails equal distant apart and square to within 1/32″. With out any belts attached the short rail is 1/4″ off from end to end. I measure 8″ gap on one side and 8-1/4″ on the other side. I try to make it even, but I can see my middle assembly twisting. If I anchor one end and pull the other end even, it will relax to about an 1/8″ to 3/32″ off but any slight bump and it goes back to the 1/4″. It appears that my middle assembly is not perfectly square. I do not see where I can really adjust this.
I should also mention I tried with the long bolts in the assembly tight, snug, and loose and it sis not seem to have any effect.