I plan on getting almost this close to the board as the marbles are characters
in an animation I'm planning, so the black line would show up. In both of
these shots, the cone is down, into the board. It's hard to tell with no other
frame of reference, and these were rendered without perspective.
Here's a boolean intersection of 2 nurbs. I moved the green surface down until
the middle indent was exactly even with the top of the board surface. You can
see it is again close, but has rendering problems because the 2 surfaces are
too close. If I pull it up a little, then I get a noticable ring rather than a
smooth blend.