I have been drawing in Sketchup and moving my geometry to 0,0 with the top at z=0 so that I can cut it in Cambam with the default stock suface at z=0.
I export to a Collada file and convert it to 3DS with Blender. Then open in Cambam and set up a horizontal Profile3dMethod cut. I have a little decorative surface about 2"x2"x.5" that mostly comes out nicely with a 1/16" ballnose, .2 stepover and a lot of patience. The mesh is based on a 2x2 square at constant depth but i lose the depth at the top of the square.
The problem is that on each depth increment, I miss another line at the "top" of the mesh - along the x axis at maximum y. This leaves the correct shape over most of the volume but an uncut wedge up from the floor to the back of the shape.
In the picture, 0,0 is off the bottom. The ruler is along the Y axis. See how the floor ramps up moving to the top edge at upper left?