It needs to be level to 0.0005 inches which means a DTI on the cutter head. I also have no way to adjust the bed / axes. This is a CNC machine, not a 3d printer and it is made of solid aluminium with lead screws, so pretty substantial. The PCB is not level in a lot of ways so if I probe 16 points they will be up as well as down on the front left reference point. If I put double sided tape over the whole of the back of the PCB and make sure it is firmly stuck to the bed all over then it will be OK without the auto Z adjust but then you snap the PCB taking it off. The bed itself is smooth, flat and level WRT both the X and Y axes, sticky tape and cheap copper backed board add a variable that can only be accounted for by auto Z adjust.