RE: [CAD_CAM_EDM_DRO]floating z axis

>This will likely drag highly abrasive grit under the pressure foot, and
>chew up either the foot, the board, or both.

I played with this when I built my first router out of printer steppers,
round
bar and 1/4" plate back in school.

I used a dremel in the head, and I connected the routing bit as one side
of a
limit switch, and the PC board and bed as the other. That way the
software could "feel" the
height of the PCB at the start and end of each cut, and compensate.

The actual motion looked quite cool, it would tap-tap-cut quite
rhythmically.

The big problem with this is that if you get islands it stops working.
You either
need intelligent software to re-order the cuts to avoid isolation
problems, or do
what I did and re-order them manually for each board. I never got past
that though.

Now that I understand the math better I would measure the height of the
board on a
.1" grid, and then add Z offsets to the 2D milling path by simple
interpolation.
Conductive feedback is the easy way. Capacitive feedback will avoid
problems with
oxidation on the PCB, and avoid the grid of dots you'll get otherwise.
Or you could
use a digitizing probe.

Regards,
Nic.