I thought I would share this since it is making its rounds on Hackaday and Hackster.io.
One of the main uses for CNC machines like the Mill One is
You can of course, also check out Ayesha’s tutorial on PCB milling (https://sienci.com/2018/08/23/pcb-milling-tutorial/), which goes through a similar process.
Looks like according to comments online that the next frontier to getting good milled circuit boards is to use a mesh leveling system. This would of course map out all of the points on the PCB and automatically raise and lower the Z axis to compensate for any irregularities in the thickness of the board.
Chuck, from CHEP3D, also covers PCB milling on the Mill One, with his own way of using Easel.