Java3D - Z-buffer clearing and frame drawing

I was wondering if it is possible to clear the z-buffer in Java3D, to make use of i.e. skyboxes…

Also, I have not figured out how to completely redraw a scene in one frame, in other words: is it possible to redraw the scene manually, without Java3D having to do it in a separate thread? Java3D’s way of redrawing the scenegraph often makes animations look choppy as it doesn’t seem to update all vertex positions each frame. And I understand that, because how should it know that the frame is done? I saw someone mentioning the use of behaviours…?

-Trond