I've had some leftover MDF from a previous project which I want to use as my main building material. The Idea is to take two MDF boards and use them as a really cheap axial ball bearing. It has to bear virtually no load (the biggest Lego contraption that can conceivably fit on the thing will weigh less than 1 kg, the Nanoblock models way less than 100 g). The reason why I decided to go for the ball bearing is the very little friction, so I can turn it by hand without ugly stick/slip effects and lateron automatically with a very tiny motor in very tiny steps.