Excessively low resolution but here's a 60x timelapse of what I'm doing:

I start by lining the cutting bit up with some target holes drilled from the other side, to align it with what's carved into the other side. Then it runs around measuring the height of the copper. Then it starts carving and it's apparently almost immediately that it's cutting too wide and too deep but there's nothing I can do about it at that point so I just let it finish for the video. Then I drilled the holes so I could check their alignment with the other side.

I don't know why but on the left side of the board it was cutting at a depth of about 1 mm, when it's supposed to cut at 0.175 mm. The width of the cuts appear to be at least 1 mm, whereas in order to get the 25 mill traces I'd intended it needs to be 0.635 mm or less, which it was in a previous test. So I have some shit to figure out still.

You can see in the video when it's drilling holes that the board flexes downward. This was apparent before I did anything, but I expected it would be fine since the bed mapping would account for the curve of the board, and indeed I have no idea how it would have made it cut deeper unless the board curved upward even more as it was working.

I need to write some stuff to test the code I wrote to control the cutting depth relative to the copper height. Also it would be nice if there were some way to abort without resetting the machine and if it were possible to adjust the cutting height on the fly, so I'll have to add those features as well. As soon as it began I wanted to stop it and play with the cutting bit to see if there was anything I could do to make it cut a thinner line, but once it starts cutting I can't do the bed mapping again because some of the copper isn't there, and so I can't reset the machine to stop it and expect to be able to start it again.