Here's the machine actually working! I put together a very simple demo page in Inkscape to make sure there would be no nasty surprises (there were), and I'm ecstatic about the outcome.

The first issue was the backlash on the X-axis. As previously mentioned, that ball screw arrived slightly bent, and it shows (look between 3-4 o'clock on the circles). Not only is it on the order of 10x worse than the other axes, it's not consistent across the length - huge on either end and negligible in the middle. The screw has to go.

Second issue is the obvious lack of bed leveling - not a huge deal as the tools I'm waiting on include a bottom cleaning bit (seriously, who named that?), which will plow through my sacrificial MDF like butter. I'm also in the process of rebuilding the whole thing, this time actually paying attention to abstract concepts like "square" and "true".

I'm guessing the whole slippery-pen-in-zip-ties tooling played absolutely no part in the inaccuracies, as I can assure you zip-ties are still an integral part of keeping heavy industry running :)

Back to work for another 8 days, but I'll have a spindle and tool set waiting for me when I get back.