I have been successfully creating CNC routed prototype PCB's for some time. Over the last week I have been experimenting with laying a solder mask over the routed PCB and the milling off the mask on the solder pads. I have not been at all successful and I cannot fathom the cause of the results. I am using K-CAD to generate the G-CODE for the job and using the electric sensing probe to set the tool height. I hope my problem is demonstrated with the attached picture.  The red board has been isolation routed and as you may be able to see some of the pads have been completely cleared away and others are perfect. I used a 60 degree 3.125mm chamfer bit and my first thoughts were that the variations in the thickness of the PCB would cause this issue. The second attempt (labelled 3) is the lower black attempt that isolation routed ok, this time I used a 2mm conical bit and it shows generally the same pads being cut through although this is a newer area of the blank PCB. The G-code definitely shows the Z depth to be consistent over the job when I checked the code. The third attempt (black, labelled 2) was using a 0.1mm flat conical bit (no isolation routing prior) and again the pads previously destroyed are the same ones even when others are missed completely. I am at a loss to see what is happening here and how I can fix it. 0A47
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