Hey Thierry,
Thank you for all those ideas. I had already unscrewed the brass thread by about 1mm on both sides. That still didn't fix it. It turns out that the Z axis started to operate better, maybe even normally, when I unscrewed the bearing for the left smooth rod by about .5mm. The metal mounting plate is crooked and it was forcing the bearing to sit at a slight angle from the rod.
I successfully printed one correct layer of PLA!!!
Now I have to figure out why the next layer started about 2mm above the print bed. There's probably already some material on calibration here on the forum.
And, of course thank you, _kaktus_ for all your help so far and for the encouragement. The amount of time I had to spend getting this far was pretty big but I do feel strangely accomplished somehow.
