That's a really helpful article - thanks very much. It gives me some confidence as I approach my first Carvey PCB job that it might actually work out.
I had to work through the overlap procedure for myself to make sure I understood it, and ended up with a formula for the tool diameter to enter into Carvey for each pass.
If the bit has an effective cutting width of CutWidth (0.3mm in your article), and the overlap as a percent of the cutting width is OLapPct, then the amount the tool diameter increases on each successive pass is
Spacing = 2*(1-OLapPct)*CutWidth
If Pass is the pass number (1, 2, ...), then
ToolDiameter = CutWidth + (Pass-1)*Spacing