carving question

["George Graham" <georgergraham@zzzzzzzzzzz>]

Andrei,
I'm not sure that I understand exactly what you mean by a v like shape
between the surfaces. So the direction I'll go in might help, and if not,
please forgive me.

If I'm trying to join together two curved , rounded marble forms, and leave
a void between them, that is a special shape, then the first and most
important step is to draw lines on the stone that tell you exactly what you
have to remove. To get to a point where you can layout the lines I've got to
position the stones in the finished position. Exactly! Then you can start
making guide marks and lines that will let you separate the stones for the
carving and then put them back, in the same place.

When you first put the pieces together in the finished position, and need to
draw a straight line on a curving surface, to for example layout a line that
shows where to slice a section off the surface of a sphere, the easiest way
would be to use the laser line tools that builders use to mark a line around
a room that would make it easy for the carpenter to put floor molding around
the wall that all comes to the same height. Once the laser is set to the
desired height, turned on and wherever the light hits the wall, its marked
with a pencil, and then the dots are connected. These gadgets are showing up
at all the home builder supply stores, and are surprisingly cheap. They come
in a lot of different styles to meet different needs. You can do the same
thing with straight edges, squares and levels, and a helper.

No doubt , you will have to come up with a solution that will be unique to
your project.
Good luck!
George Graham