[gorkish]

IMO fully mechanically milled PCBs are kind of stupid; you are never going to actually manufacture them at scale this way, so what is the point in jumping through the DFM effort to prototype with such a constrained process? There used to be a cost and speed advantage vs using a service provider, but pcbway and jlcpcb have absolutely changed the game on that front. There still are advantage for in-house manufacturing capability, but I don't think pure milling is a good approach - whatever small scale process you use for this needs to produce an end product that is highly similar to the mass manufactured process and as such will require mechanical (milling/drilling), optical (etch/ablate), and printing (mask/silkscreen) processes. I think there are some small machines getting quite close to automating the one-off production of 'real' pcbs, though.