Hi,
I'm successfully milling PCBs on my cnc. The cnc is custom made but it is a small one with aluminum profiles frame and not very stiff. I haven't milled PCBs this big. My biggest is around 50mm x 50mm. I use smd components so I use two v bits one is 0.5 mm 30 deg and one 0.2 mm 15 deg (or maybe 20 deg). I use a double sided tape for holding the board. I use estlcam, but the software should not matter. I use flatcam for the gcode generation. So for 0.2mm bit I use 250 mm per minute and for the 0.5 mm one 350 mm per minute. The process is like this. I first make surface scan. Then mill with the 0.5mm at around 0.08mm - 0.1mm. This should remove the most copper (I make isolation milling 3-4 passes). And then mill with 0.2mm one at 0.1 mm depth (1-2 passes). I get the Z zero for the 0.2 mm around the lowest point. If the bending is more than 0.05 - 0.07 mm. I try to get it at higher point but never to have depth less than 0.05 mm. Also I try to make my traces thicker with the thinnest 20 mils if possible so bigger depth of cut do not make them too thin. Another thing I do is mill a waste board flat and hold it with just few bolts to the table and stick the PCB to that waste board. The speeds are probably quite slow. It takes quite some time to mill a board but I can leave it and do something else. I hope this helps. I'll share some photos in the evening.
Svetlo
