Not quite sure where this should be posted, but since in the end it is a design question - this seems as good a place as any. Basically, I have an object which I had printed. The object has a mostly flat surface. However at various locations on that surface there are spheres. Each sphere has a diameter of 0.3 mm and it is sunk half way into the surface (so that 0.15 mm protrude from the surface). When I had the object printed most of these spheres seem to have not printed. Some did, however it seems that there really isn't a specific reason why a particular sphere printed while a different did not. What size does a detail actually have to be in order to be printed reliably every time in FUD?