Michael,

>Ideally I guess you would never build a new loft surface at all and just take a whole bunch of radial
>profile curves from the 3D shape and use those as your toolpaths - but I always thought that is
>more or less exactly the kind of task that a CAM program is supposed to do for you?

You are right, as far as I know, the CAM programs that support 4th axis would analyse the 3d object and the tool path but those CAM softwares that support 4th axis are way over my hobbyst budget.
My CAM program, as explained by BurrMan previously, is a "four side machining". Each side is machined in a raster fashion. The tool moves at constant speed across and within the boundary of the part and after each pass the other axis is incremented. During the whole process, the tool follows the peaks and valleys of the object.
One option is to machine the top part with normal xyz operation, rotate the part 90 degrees, machine the side then repeat for the bottom and the other side.

Colin told us that the Flow command in Rhino4 does exactly what I want to do (see the tutorial attachement to Colin's message 2654.8)
As Moi3d does not have such a command, my idea is to draw the object in 3d, then modify it so the CAM would "think" it is machining one side of the part while in fact the object would be rotated and the entire machining would take place in one operation.

Gaston
My idea was inspired by Julian Beever's sidewalk painting.
http://users.skynet.be/J.Beever/dungeon.html