I spent all weekend taking it apart and tweaking it.
The biggest improvement in eliminating vibrations was re-balancing the wheels. It's possible there was moisture in them from the glue up and as the glue dried and the wood around the glue dried, the balancing I did before had to be tweaked a little. Although it's also possible that I just did a shoddy job last time.
Also, a big improvement was that the pulley on the drive wheel was 20 thousands of an inch out of round. So I spun that wheel up again and very carefully used a chisel to get the pulley groove round. I could feel the chisel wanting to rock back and forth with the pulley as the wheel rotated each time, so I really held it tightly against the tool rest and just eased it ever so slightly against the pulley to nibble gently away at the higher side as it came around. I could hear a bit of a pulsating cutting sound as it only nibbled away at the high side. Once the sound became constant cutting, I stopped. When I measured it again, it was 5 thousandths out of round.
Then I turned my attention to getting the wheels lined up better. And I started taking pictures.
To get the top wheel directly over the bottom wheel, I needed to pull it forward by 8-9 mm.
So I started by removing the brackets that hold the entire top wheel assembly in place. Fortunately they are just screwed on. No glue.
Then I cut two shims 8 mm thick.
I glued the shims to the uprights.
And clamped them to dry
